Devin Devine, traveling stone mason based in the Poconos
devin@devineescapes.com
phone consultation services
DIY hardscape/masonry/flagstone help rates:
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What to put between flagstone joints–polymeric sand or stone dust?
(UPDATED in 2023–yes, polymeric sand is still a joke)
TL/DR = polymeric sand is plastic goo and sand mixed. Extensive study has determined that plastic is not needed within your landscape and in fact plastic is a toxic addition to any landscape.
Polymeric sand is sand with an acrylic binder added. I first started seeing this stuff about fifteen years ago. Its popularity increased steadily for a decade and now it is a very common landscape product. Common does not mean “good”. They come out with new gimmicky products all the time, new products come and go.
Polymeric sand, or “poly-sand” seemed great at first. As easy to install as regular sand, almost. You simply sweep the material into the flagstone (or other paver) joints, lightly hose down, then it solidifies. Once it dries and hardens, the sand stays in place. It does not get dug out by ants, weeds can’t grow through it and it does not wash out. Sounds like a winner, right? Well, it’s more complicated than that. Below, we’ll examine these advantages one at a time.
But how’s my work hold up–using only natural ingredients?
No geotextile fabric, no polymeric sand: the old ways work best.
Patio I built in Northern California circa 2018. If a project interests me I can be convinced to travel.
Essential tools for flagstone installation:
- GRABO, the hot new vacuum lifter that makes lifting flagstones a bit easier. My review can be found HERE.
- dead blow type mallet. Many types to choose from….lately I mostly use my rawhide mallet, but the rubber headed modern style .deadblow is in my tool bucket too, and I’ll use whichever is closer on hand.
- brick hammer, for cutting flagstone.
- with diamond blade.
- Angle grinder. Same one I use. Keep this on hand for cuts that the hammer won’t successfully make, or that will take too long with the hammer
- Diamond blades.
- Brick chisel.
- A couple of 5 gallon buckets (for stone dust, when leveling stones)….shovel, wheel barrow…..4′ level
- Pick maddock. Best way to dig. Break up soil with this, then use shovel.
- Knee pads–essential.
- Hand tamper and/or plate compactor. For 100 square foot or less, I’d just use the hand tamper. Bigger than that–you might want to rent plate compactor.
Reasons why stone dust is the correct answer for in between flagstones:
1. Easy to install. Well, it’s fairly easy, but you have to be careful–the sand is mixed with a binder. Use too much water and the binder, an acrylic glue, washes out and leaves a nasty haze all over your carefully laid flagstone. Also, do not have the hose on too powerful of a setting, or you can blow the poly sand right out of the joint, and get it all over the flagstone/paver/whatever. This can trouble novices and pros alike. You also have to be very careful that the joint is filled all the way, and also make sure that there is no material left on top of the paving units, before you hose down. As such, when maintenance issues do arise, you probably want to call a pro and have them deal with it.
Stays in place
2. Stays in place. Sure, but not forever. Polymeric sand is generally intended for dry laid paver applications. Natural flagstone, concrete paver and ceramic brick patios and walkways are set upon gravel foundations, their joints then need to be filled. One of the beautiful things about dry laid patios is that the foundation can withstand freeze and thaw without cracking like concrete will. Paving units will shift slightly, especially in colder climates with a freeze thaw cycle. Polymeric sand will crack, over time. This will lead to headaches. Furthermore, the polymeric sand stays in place because it is glued together and also glued to the stones or bricks it is placed between. it will likely stay glued to itself….but the bricks or stone that it is set amongst–these will not be clean surfaces. Separation will happen. Cracks will form.
3. Weed and ant proof. Polymeric sand is indeed pretty good on these fronts….for the first year or 3. But tiny cracks do form, and weeds will get in there, roots will grow, cracks will get worse.
Related content: how to level flagstones in stone dust and use stone dust as a joint material
Related Content: Paver Base, no more need to excavate, no digging required patio installation?
Fit those stones together nicely:
What I use is stone fines AKA screenings. First, lay a foundation of compacted stone aggregate, then lay individual flagstones using screenings as the leveling agent. Once all the stones are laid, sweep more screenings into the joints. Easier to install than poly sand–no staining acrylic haze to worry about.
Stone fines
Stone fines are heavier than regular sand, thus they will not wash out quite so easily. Really, the screenings are made of small chips of stone, about one eighth of an inch in size, with tinypowder-like fine material mixed in as well. these fines, when dampened, actually do bind up with the larger chips, becoming semi-solid.
Fines, unlike polymeric sand, will indeed settle over time, however–and that is a good thing! Read that again–stone dust settling down in-between flagstone is a GOOD thing. Small voids may be left underneath your paving units–especially if you are using irregular natural stone. Even if you are using a more uniform paver, the gravel foundation may not compact 100 percent perfectly. Small voids may form. If you used screenings as both the leveling agent and as the joint filler, this is no big deal. You simply sweep more screenings into the joint and life is good, with no great worries at all. Ahhh, it is grande indeed.
Polymeric sand, in the above scenario, will either crack up, or, worse yet, it may stay solid on top, leaving that void beneath, causing more problems until the poly sand finally does crack up. This includes gator dust and any other type or brand of polysand. Bad news, that stuff.
Ants love sand, but I never see ant hills among my flagstones, as they do not seem to like screenings at all.
Polymeric sand cracks up
It leaves a nasty haze all over the place, and is overall a wasteful, expensive mess and a disappointment. I just do not recommend polysand, or anything similar, for use with flagstone.
Fact is you can build awesome and beautiful and enduring things for your landscape, without using any plastic. Check out my all natural stone art:
Related content: dry stone mosaics
stone sphere sculpture in Walnutport Pennsylvania, built September 2020. Visible from the road, near blue Mountain Ski Resort. Private commission.
Related content: dry stone spheres by Devin Devine
Now about weeds…what can I say? Life happens. Every once in awhile, you may have to pull out a weed. You could spray Acetic acid (vinegar) into the stone joints, deterring weed growth. Another method is to simply pour boiling water on the unwanted plants. Simple, right? There’s other ways to deal with weeds, but this article is getting long. (you can always just let the “weeds” go….) Just don’t spray any poison into there, please and thank you. Again–do not spray round-up or any other poison unto your patio. Seriously, that will not go over well at all.
Finally, polymeric sand is an acrylic product. Plastic. Really, do we want to build plastic landscapes? A bit of a philosophical question, really. Please consider it for a minute.
Here is an excerpt from another article that I wrote on this subject:
The real problem with polymeric sand
In addition to the nasty haze staining your flagstones surface, the toxins that leach out into your lawn and garden, the environmental impact and the wasted financial resources…the technical problem, the reason why polymeric sand ruins patios and walkways is this: polymeric sand makes it too easy.
Polymeric sand makes people think that they can cheat, that they can get away with wider joints than they would otherwise. Fact is that you simply can not use polymeric sand as a replacement for taking your time and doing the job right. You could a) hire a professional. b) take your time, read all the above articles, and educate yourself well enough to try your hand at a hard task or c) go ahead and live in a lame world where “you don’t need to fit your flagstones together right…you can just fill the spaces in between with plastic!” Doesn’t sound too ingenious, when stated that way, doesn’t it?
Kind Regards,
Enjoy these articles for free! But if you want one-on-one help, I am happy to offer consultation services. I do this all the time.
But please feel free to post brief, simple questions below, as comments to this thread. That way my answers can help you, and others as well.
Do you need hardscape help? A professional, who will talk with you on the phone, and walk you through the process of laying flagstone, repairing flagstone, or any other such situation? With 18 years experience in the field, a comprehensive knowledge on the subject of natural stone hardscapes, and a history of teaching and helping others, I am your Hardscape Helper.
DIY hardscape/masonry/flagstone help rates:
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DISCLAIMER
This article is intended to be informative–primarily, to let my customers know how and why I do my work. If you are the DIY type and you find this helpful, then great. Feel free to ask questions in the comment section below. I, of course, can take no responsibility for your work or for your landscape (unless you hire me) but if you are doing it on you your own, then I wish you luck and I’ll try my best to answer your questions.
I do flagstone and dry stone wall projects all across the country, and I’ve found stone dust available everywhere I’ve worked. I’ve seen it called screenings, quarry dust, quarry fines, grit, Decomposed Granite, quarter-inch-minus, pathway fines….etc. I hope this article has been helpful.
If you quote this article or re-post it, please give proper credit and link back to my site. Thanks!
Attention, DIY flagstone people!
I am happy to offer all of these DIY flagstone articles for free. This is professional advice, written by dedicated a stone mason/passionate stone artist with over 25 years experience. One who just happens to enjoy writing, and likes to help people.
Thank You
Thanks again!
Good luck!
Great information. I was wondering… I have put all my random flagstone down on the screening. Now I am stuck with what is the best material to fill the cracks. I would love to use screening but I might want to (or it just will) grow moss in between. The area is shady and I imagine the main part of the area will grow moss but the pathway off the larger area might get a little sun so maybe not there. Can I still use the screening and will moss grow in it? What if I use the yogurt method etc…? Or am I better of using top soil? Please and thank you,
Freddi
You’ll be fine using screenings. In the shady area moss will grow in the screenings, in the sunny area, maybe not so much. If you want you can promote moss in the shady area–put some moss in the blender with old beer/buttermilk (perhaps this is what you mean by the “yogurt method”?) and pour the slurry atop the screenings to get the moss to grow there. Or let it happen on it’s own.
Good luck with it, whatever you do. And have fun! Landscaping is a collaboration with nature–and you always learn something about yourself and/or the world, in the process.
Thank you Devin for this, preparing to put in quartz flags in Colorado over clay soil, gravel base, love this long term solution you provide with decomposed granite for leveling and filler. If I keep the joints tight will the material bind enough to keep water from percolating into ground? I’m trying to keep my foundation dry on north side of home.
Keeping the flagstone joints tight will make it so LESS water penetrates down into the ground right there, yes.
Make sure the patio is pitched hard enough. 2.5 inches over a ten foot span will be enough, provided there are no major dips. When laying the flagstone, I use a four foot level….2.5 inches over ten feet is equal to 1 inch over 4 feet. So I use a 4 foot level. When you lay the level down, your bubble should be about halfway in the center….and you do not want much space beneath the level anyway….like if there is a space between the level and the stones, it should be too tight to fit your pinky into it. A gap much wider than half an inch will become a minor puddle spot–and that water will go down into the ground.
Hope that helps. Good luck!
Where do you buy your screenings in Pennsylvania? I am located near Blakeslee and want to get quality screenings for my flagstone project.
903 landscape supply is the place: https://www.903inc.com/
Devin, Thanks for the article. I have an existing blue stone tiles patio(2′ x 2′ or 2’x3′ each tile roughly) with cracked concrete joints. We need to replace the joints and extend the patio 10 feet. Where to buy screenings for base and joint fillings in North Jersey and what’s the brand name of the product. I am planning to level the ground and place landscaping cloth below crushing and lay stone tiles. Fill joints with screening. please reply with name of screening, where to buy and if method i am thinking is good.
I don’t use landscape cloth beneath a patio. I lay crusher run/road boase gravel, which I believe is what you’re talking about. Screenings is used as both the leveling agent and as the joint material. But screenings are only used in dry laid application. If your existing patio has mortared joints, then it likely is built upon a concrete foundation. If it’s built upon concrete, then it should be repaired with mortar. If it’s dry laid, then everything should be dry laid–no cement based products.
My dry laid process is described here.
And here is how I repair mortared joints
If it were me, I’d repair the existing patio with mortar–and then probably do the additional 10′ dry laid. Dry laid is hugely my preference, in any place with a freeze-thaw cycle. But, it depends on the scene, and on your preferences….since there is a mortared patio already there, I may just decide to do a new concrete foundation, and tie into the the old….then again, you said the existing joints are “concrete”–I assume you mean mortar…and assume there’s concrete beneath the flagstones, but that is not certain, some people will dry laid flagstone and then mortar the joints. Such joints will fail within a few years. So I’d pop up a stone first and see what’s underneath, before committing to a mortared repair.
Screenings are sold by the name “screenings” in New Jersey–although some places may use the name “grit” or “stone dust”. Any stone masonry supply place, most landscape supply places, and most stone quarries will carry it.
I just installed a natural stone patio and was researching poly sand for filling the cracks when I came across your article. I have 1/4 minus which I used for the bed. Will this work to fill the cracks of should I attempt to find a finer material?
I recommend screenings–which are 1/8 inch and smaller–and contain the very important fines–flour-like, powdery stone dust. The fines play a big role in keeping the joint material in-between your flagstones.
1/4″ minus works too.
Good luck!
Devin,
What a great article. Love your artwork with stone. Seen it before and everyone’s gift is unique.
Thanks for your colorful commentary and your insight (with years and years of experience).
Brett in Millersville,PA.
I’m glad that you appreciate my work. Thank you.
Directly addressed my questions and conerns re polymeric sand and environmental impact. Very helpful, thanks.
Awesome, you’re welcome and I’m glad to help.
I appreciate the advice. I had been tempted to use polymeric sand, but plan not to use it now.
Hi – We are going to try and repair some ancient stone walls on our Martha’s Vineyard property. The original builders certainly didn’t follow your wall building principles (😊) so I guess neither can our repairs. Any idea where we could look for some advice? Thx
Sounds interesting.
I do phone/email consultations for $93 an hour. A site visit could be arranged, if necessary. Send photos and info to devin@devineescapes.com
What can I use for 4 inch wide joints
I’d use stone dust….but if possible, I’d tighten them joints up a bit.
Do you recommend a sealer be applied at all?
I do not.
Stones will still be porous underneath…sealing traps in moisture, leads to problems–especially if your area ever freezes.
More info:
Sealing flagstone?
I’d like to schedule a consultation for n outdoor porcelain paver project
I can help you with that. You will receive an email from devin@devineescapes.com Once you’ve selected a time, I can accept payment via venmo $123 for a 1 hour consultation: https://account.venmo.com/u/Devin-Devine-3
Where do I buy screening? A stone or sand quarry or can I get it at the hardware store?
Where do you live–it’s only called screenings in Pennsylvania and New Jersey. Unfortunately every place has their own names for it. Rock dust, pathway fines, etc.
Stone masonry supply place. Landscape supply. Any gravel quarry will sell it as well.
I recently laid down a flagstone patio in sand and used sand to fill the joints. I wanted something that would promote drainage and have a natural look. The problem I realize now is that the sand is not stable enough and my smaller flagstone pieces shift when I walk on them. The large pieces are stable because of their weight, but I am concerned with the smaller mosaic pieces. I am considering taking the sand out, re-leveling, and filling the joints with screening instead. Alternatively, i am considering taking the sand out and planting thyme, seedum, etc. in the cracks thinking the soil and plants will help hold the stones in place. Any thoughts?
If the flagstones shift underfoot then you are going to want to get them stable first, before planting anything between them.
One stone at a time. Push down on it, one corner of the stone at a time. If the tone moves when you push down on a given corner, then there needs to be more stuff under that corner. Shove some stuff under there. A little bit more than you think it needs. Then gently give it a few taps with a mallet to seat it into place. Check it again–repeat until it’s wobble-free. There’s a lot of different ways to go about getting a flagstone stable. Just approach the work with heart and you’ll be alright.
Will smaller flagstones be stable, or do you need to use larger slabs? I would like to use something called a tumbled Colorado Red Stepper which is relatively small compared to other stones. The previous comment about the smaller stones becoming loose made me wonder if using the red steppers will work.
Here is a picture of what they look like
https://www.rmtnlandscape.com/products/flagstone/1131-colorado-red-tumbled-steppers2
Also, in your article about using gravel, can you use AB3 or Crusher Run? I am in the midwest and that is the closest thing I can find that probably matches what you described in your article.
Thanks for your help
Some of the stones you’re showing me look a bit on the small side. That doesn’t mean that they certainly “won’t work”….but as a professional, they wouldn’t usually be my first pick. Having decades of experience, I can make this type of material work–by fitting them tight, malleting them into their bedding material, maybe using some of the smaller ones upright–or not at all, and other tricks I’ve picked up over the years–but still at the end of the day, a dry laid patio built with this sort of material will probably not be 100% wobble free at job completion. Maybe %90. That number will improve, over the months, as stones settle in.
Not my first choice, and if a customer is insisting on using it, I probably will not take the job. However, it may be fine for DIY purposes. Need your patio be perfect? How much foot traffic are we expecting? Is this stone in question local, or otherwise desireable to you? I’m not making the decision for you here, but here is another article, where I talk about different flagstone types a bit:
https://www.devineescapes.com/what-type-of-flagstone-to-use-for-your-patio-or-stone-walkway/
As far as the gravel goes, crusher run is the stuff. Low void content, contains fines, is used as road foundations. Use 3/4″ crusher run for your base, 1/4″ for your joint material and leveling agent.
Devin,
Thank you for your very fast response and for taking the time to answer my question.
I am not wedded to those tumbled red steppers. I just saw them at the rock yard and thought they looked attractive because of the effect the tumbling had on them. I never thought about the problems I would encounter using small stones on a dry-laid patio. This project will be my first. Thanks for pointing this out.
Great, you’re welcome and I hope my advice is helpful. Good luck with your flagstone project!
Every time it rains, screening from my joints splatters into my stone and patio furniture. Any suggestions to avoid this?
How old is your patio? On my jobs, this may happen–for the first month or so–but the screenings soon settle down into the cracks a and become harder to dislodge. Most of my jobs are in Pennsylvania. Please do remember folks, local soils may vary. Perhaps the stone dust/screenings in your area are different then what I have access to. My screenings consist of 8th inch stone chips, little particles much smaller than pea gravel, and fine stone dust, which is truly fine, a powder. These fines harden up, almost like a binder, and after enough cycles of rain and sweeping the stuff back in, it eventually just stays there. Also on my jobs the joints are maybe an inch wide, or less….I’ve seen other hardscapes where the flagstones have 3″ gaps between them–try keeping anything in there. It’s just too big.
Good luck!
Great information and encouragement!
Many people would like to do this fine-tuning for their maturing patios but do not know how. It is good to know that pros have to take it stone-by-stone and be patient. Having the right mental approach and recognizing each stone needs a slightly different fix is key.
Well said. Thanks!
Hi – helpful article- thank you. I have old flagstone with sand in between. I had them power washed so a lot of the sand was blown out. Can you suggest how I might fill in what was removed? Thank you
Sure. I recommend washing out the rest of the sand. Ants love sand, sand washes out more easily than stone dust, so I’d remove the sand and replace with stone dust. My process is described in this article: how to fill flagstone joints.
Scroll down to the heading that says “How to install stone dust in between your flagstones”.
In short: sweep the stone dust into the joints, hose down. The material will settle when you hose it down, so repeat. Leave the joints about a 1/8″ – 1/4″ shy of the tops of the flagstones when you’re finished. The article goes into more detail.
What is the best crack filler between a natural flagstone patio. I have tried poly sand (with the correct amts of watering)but find that the sand forms a crust, other areas may be soft and mushy, and if I dig down it is not solid. Yes I have run experiments oin differenat areas of the patio and have used different amts of water with the same results. Definitely not solid after days in some areas to wks. Worried about chair legs busting through. Thinking of switching to concrete—-frustrated poly user….help
As mentioned in the article right above……..I go with screenings. Re-read the article please 🙂 Actually, I’ll go back and edit, put a few words in bold and make it a bit more clear.
Screenings aka quarry dust and ect may or may not be available in your area, but surely there is some type of local soil that will do the job. Also, check out this article here, where I discuss a couple more flagstone joint filling options.
Great article… any concerns with using decomposed granite within a flagstone patio around a pool deck? It would drain away but I assume some of it may get tracked into the pool.
Good question. I’ve done this once before. My customer wanted no transition between the pool and the patio…..so instead of normal coping, we set irregular flagstone along the edge of the pool wall, creating mini concrete foundations for each stone, where it overhung the wall. These stones on the pool edge got mortared in joints, dyed dark gray to match the stone dust/DG that was used for the rest of the flagstone. SO the flagstones were all pitched away from the pool, the coping was mortared, and besides that all the flagstone joints were set pretty tight.
Haven’t had any issues of stone dust getting into the pool, 3 years later.
Now, my joints were set tight, maybe half inch wide…wider joints than that might be an issue. My plan was to go with a fairly tight joint for the whole patio but then get even tighter for the 5 feet or so immediately close to the pool….in the end, I think the entire patio got a half inch joint, maybe more like three eighths to a quarter inch, for the few feet closest to the pool, but no major difference, just a smidge tighter right by the pool.
And be sure to not overfill your joints–the stone dust/DG should be a bit shy of the tops of your flagstones. The flagstones, having not perfectly flat surfaces, means that if you fill the joints all the way flush with the tops of the flagstones, then that joint material will spill out. When I’m done, the joint material will be about a quarter inch from the tops of the stones.
Devin-Way to go! You have the right idea about creating “a good wholesome and fun place” to be with family and friends. Thank you. I think I’ll try the screening stuff. I’m doing a small extension of a patio leading to a path about 200’x18″. I have a circle design using left-over holland pavers; so there are cracks. I think your solution is the answer. Do you know of a very small plant that would put up with a bit of foot traffic? I want to use it in a few places and if it had a light blue blume, that would work, too. God’s peace. Jeff
Hey Jeff. About ground cover for in between your stones….there’s a few good options out there, like Irish moss (not really a moss) and thyme and others. Site conditions will of course determine which will work for your spot. http://www.stepables.com/ stepables . com should give you all the help you need in this regard. Good luck!
Devin, have you tried NATRACIL as a stabilizer? It is not a plastic based material, it is from psyllium husks. You mix it with the fines and sweep into the cracks, moisten. It’s been working for me. I haven’t been able to find much info about it so I really hope it really is a “natural” alternative to polymers.
Psyllium husk joint binder is, as far as I can tell, a lot more natural than an acrylic based product. I’ve never studied it, never used it for a client and been unable to study its utility over the years–which is a major omission on my part. I remember reading about psyllium husks being used as a stabilizer, back in like 2009 or 2010, so major omission, I suppose, that I still haven’t studied the material hands-on. Fact is, no one really uses it, so I never encounter examples of good, or bad installations using the product. Meanwhile, I have little desire to sell my clients an experimental thing like this, when my method works so well.
But here’s the problem: polymeric sand fails….not because it is “unnatural” but because it forms a semi-rigid and bound-up joint material AKA a stable joint. This is a BAD thing. The material beneath the flagstone may settle. The joint however stays put….now you have a hollow void, either underneath the stone, or just beneath the joint. The stone settles, the joint cracks. Bummer. So…..what good shall it do me, if this unfortunately rigid and stable joint is natural, not synthetic?
I use, and recommend a stone dust joint, for dry laid flagstone applications. Or sand, if need be. Or small pebbles…..but the thing is, that small voids may likely form beneath some of your patio stones. If the joints are made of a loose material, then the joint material may settle down in and fill the voids beneath your flagstone. This system is somewhat self-healing. Void forms beneath flagstone….joint settles in and fills that void–then you top off joint. Now picture that scenario with a rigid joint. Void forms–stone sinks–solid joint sits above void–joint cracks.
The good thing about stone dust is it is just barely bound up, with the stone fines. STone flour, such a fine dust that dampening it somewhat, sorta binds it up. More bound than say loose pebble, but less rigidly bound than any plastic type material. You can make plastic from plants….and that may be less toxic and better for our eco system, than petrol-plastic. But then, it its still more rigid and solid than we want, for flagstone joints.
AGAIN, major omission on my part. Fact is I need to build a demonstration, a small flagstone patio, and bind it up with a psyllium based aggregate stabilizer. Then I need to study how it behaves, over years. Science demands this of me. Alas, I’ve been a bit busy with tentacles and planetoids, and also with helping DIY enthusiasts with their own projects. Fact is, if natracil wanted some publicity….they’d send me a free sample. Then maybe I’d write an article and update it once a year, reporting on how it performs and how to best maintain it.
Hello. I really appreciate your helpful content! I’m planning on building a dry laid flagstone patio, & was wondering what your thoughts are on using a paver base? I live in Philadelphia, & transporting gravel to my backyard for a 6’ base would be pretty tricky.
If you think using a paver base is do able, what would you recommend for layering below & on top of the base? Thanks!
My first thought is idk, maybe. But then I remember 15 years ago they were trying to sell these plastic cells, that looked like honeycomb. These were 2″ thick. You were supposed to fill them with 2″ of pea gravel–and they would take the place of 6″ of gravel.
They had “engineers have concluded that these panels perform BETTER than a traditional stone foundation.”
But they disappeared because they don’t work.
These new quarter inch thick versions will allow someone to successfully schnooker many home owners out of their money–but will they successfully replace 6″ of gravel?
The 2″ version didn’t work. After the present quarter inch version has failed, gained a bad rep, and then been forgotten–they’ll come out with a micrometer thick version and “engineers have tested this product….”
Just power washed my patio of stone pavers. Through the washing, exposed some cracks between the pavers. What is the best way to repair? Sand?
Sweeping sand into the joints is one way to go about it….read the article, for other suggestions 🙂
Or, check out this great article here: http://www.devineescapes.com/flagstone-what-to-use-sand-cement-or-gravel/
SHORT ANSWER: get some stone dust aka screenings. Call your local quarry.
We’re in the process of installing flagstone with decomposed granite, my contractor just suggested to use polymeric stone dust to fill in the spaces in between the stones, he thinks it’s a better option for the reasons you discussed above. I’d love to get your opinion, my gut tells me to stay with DG.
Thanks!!!
Thank you for bringing that up–decomposed granite is yet another name for stone dust. Specifically, decomposed granite aka “decomposed granite screenings” is crushed stone, made from granite. It is an excellent material for leveling out your flagstones–the best in my opinion, and likewise it is the best joint filler for flagstones.
As such, my recommendation is clear–stay with the decomposed granite!
Just finished laying a patio of large natural stone…2-4″ thick in a shaded area. Due to the irregularity of the stones the cracks are from 1-4″ wide. I read your article, thanks. Would you suggest minus (I believe here in eastern Mo. that is the stone dust that you refer to, pea gravel or something else as a filler in cracks that wide? Didn’t like the sound of the poly sand.
Pea gravel comes loose and gets everywhere, so I’d avoid that.
In cases of larger gaps like that, I’ve had good experiences using:
-larger 1-2″ river rock.
-just planting grass in between the stone. Either fulling the joints with soil and seeding, or, during the excavtion I’ll carefully remove the sod–the grass itself plus 2″ of soil and roots along with it. The, after laying the flagstone you re-plant the sod between the stones.
-moss. Shady area you say? Do a search for how to propagate moss. It’s a simple affair, really.
-Many other ground covers to choose from. Stapables.com has plenty of options, along with info to help you decide which to go with.
Great article. Thank you for the details. I particularly appreciate the advice on killing any weeds that get in there with hot water, vinegar or pulling them by hand vs using Round UP. Quick question: in cases where the polymeric sand has left a white haze on the slate as you mentioned, what is the best way to remove the haze? Is there a solution I can spray on and use myself? Thanks.
In my experience a wire-brush + elbow grease will get *some* of it up, when it’s fresh. Most solvents that will actually remove it will probably also stain the pavers anew, so they’re out. Also, it’s toxic stuff we’re talking.
Hey, I just remembered, d-limonene (an extract of orange peels, and an all natural solvent) happens to be something that you need to be careful around plastics with, as it may dissolve them. I’d wager that it would remove the poly sand haze…use proper precautions–if it does work, you will have little bits of plastic flaking off and disintegrating, which will then need to be cleaned up again in turn.
This stuff is the type of stuff I’m talking about.
It does dissolve some plastics, not all, so who knows? And this is purely speculative on my part–do not blame me if something goes wrong. Personally, I’d try it if I had some d-limonene lying around. If not, then I’d grab my oxygen/acetylene torch. This is a torch that is used to weld and cut steel–a blow torch. All around, cleaning up the poly sand haze is either a speculative affair, or a dangerous blow torch deal, best left to professionals! Good luck!
Hi Devin — I have a bunch of slate (and some stone) paths, patios and stairways, a lot of which I have built, and while they are largely stable the crushed stone I used in the joints (which matches the slates) sometimes washes out of the steeper areas especially on the two long stair paths.
I have never used a polymeric sand, and I am wondering if I made some out of the crushed stone I have (which is very fine, for filling the joints, and I have a lot of it still)? Can I buy just the acrylic binder that I can use to make a polysand to pack areas most prone to erosion, like the fronts of the stair sections or areas that get hit most with rain wash? Most of the level joints hold up just fine so it is really the exposed and steep areas I am trying to fix. Thanks for any advice on this.
Eric
Sure, you could do that. I would of course not recommend it, for reasons outlined in the article above….well, it wouldn’t be my first recommendation anyway. But it should work well enough, yes. How big are the gaps between the flagstones? Larger than half an inch= more likely to crack. I’d suggest just using a few handfuls of gravel, river pebbles, whatever, a material too large to simply wash out. Possibly free too, if you have gravel onsite. Another option–fit the stones so tight together so that there’s really no need for filler. Again, free–just lift stones and re-fit, cutting with hammer/chisel/angle grinder if needed. Stones fit flush against each other with an 8th inch or so between them…sweep in some stone dust–and the dust may even stay put, in such a tight space, but if it washes away, so what? A gap that small can be left open.
Good luck 🙂
Hi Devin,
We are having a dry laid, recto-linear patterned, natural cleft, blue stone patio installed by a professional landscaper, but I am a little worried about the size of some of the joints. There are some joints approaching 1 inch. What is the ideal size joint? The joints are being filled with stone dust or screening as you call it. This is in New Jersey by the way. Loved your descriptions of patio aesthetics and materials. I’m glad we didn’t go with polymeric sand!
John,
SHORT ANSWER: a one inch gap is fine.
I prefer smaller joints. As long as we’re less than 1.5 inches or so, than it’s really not a problem. Just an aesthetic issue. The one inch gap for pattern-cut or rectilinear flagstone….that’s what I used to always do with a wet laid job. Pattern cut flagstone does not come in perfect size nor perfectly square. As such the larger gap is probably his way of making them fit nicely–one big aesthetic concern is even spaced joints. Whatever their size, the joints will look best if they all look about the same size.
Having said all that, I still prefer to fit pattern flagstone more tightly, quarter inch to eighth an inch–on a recent 400 square foot patio that we built we had eighth inch gaps..
Filled with stone dust and in order to keep the gaps looking regular we only had to re-cut a few of them to correct the factories imperfect cutting…
Now in my irregular natural shaped flagstone patio work I will usually leave gaps averaging about three quarters of an inch wide. No maintenance issues there. So one inch gaps, I’m not sweating it too hard. Should be fine. I hope you are happy with the final product! If not then feel free to contact me via email–I know a guy who is awesome at this type of work! You may have to wait a few months since he is sought after like that, but he, does travel to new jersey.
Good luck!
Dear Devin,
If I fill joints with decampoused granite, can I pressure wash flagstones? Will screening be all over patio?
Thanks for advice.
All the best!
ANA
pressure washing will definitely break screenings/decomposed granite loose from the joints. If you wish to pressure wash a patio that has screenings for the joints, then you will have to sweep the material back into place after pressure washing.
I’ve never known a patio to be be pressure washed more often then maybe once a decade or so…Most home owners never once pressure wash their flagstones, so it is usually a non-issue.
I’m in the process of laying flagstone over an existing sidewalk. I was told to put stone dust down….lay the faly stone in place then wet the area down. Allow the stone duts to dry and bond then come back use a non-shrinking exterior grout bewteen the flagstones…..sound good?….Thanks for any input
Frank. IMO this is a bad idea. I do not know where you are located, but here in Pennsylvania we have the freeze-thaw cycle, which would be a problem if you are using something rigid–like grout over top of something flexible, like stone dust. (even non-shrinking exterior grout)
I’ve seen this many times–a dry laid patio, with a cement based product like grout or mortar in between the flagstones. And I’ve had to repair and replace many such patios….same effect happens when someone decides to cement together the cap of a dry stone wall. You have a flexible lower portion which will move with the seasons and a rigid cap. Problem.
To be fair I’ve seen exceptions! Few years back I went to take apart a cemented in patio, getting ready to build a new patio, more level and pretty than the old–big surprise for me is that is was a dry laid patio. Woo-hoo, no need to remove a concrete foundation! In my experience however, that was a rare exception to the rule.
Good luck!
Sorry for the type O’s…..obviously “Flagstone” and Stone Dust” sorry…
No problem. Sorry for the delayed response–I’ve been busy finishing up with the years work before the winter sets in.
Devin,
My front walk is flag stone set in concrete. There are a number of cracks around a number of stones. I was wondering how best to address a potential problem as winter is approaching.
Thanks.
EDIT: I’ve also addressed this question in a previous blog post here: http://www.devineescapes.com/flagstone-repair-explained/
I’d use a 4″ angle grinder with a diamond blade, grind out the cement around the cracks. You want to go maybe 1″ deep and maybe 1/2″ wide. Or grind out the entire joint between the flagstones. Clean the joint of all dust and debri. Wait till the joint is somewhat damp, but not soaking and the fill with mortar. Mix up type S mortar mix…pre-mixed stuff is fine. Get the cement to a dry-sish mashed potato-like consistency and fill the joint, pressing down firmly.
That’s about the best I can answer….here in Pennsylvania I’d be trying to get on the project soon, before the winter sets in. Just make sure to do the project at a time inwhich the weather is not expected to get below freezing for a good 48 hours or longer.
That’s the basic formula. Are you trying to get a close match for the new mortar, color-wise? If so…well, that’s a whole ‘nother question entirely. Also, are their any loose flagstones? If no to bother questions, then the project should not be too hard.
I’ve tried my best and I hope this helps–either helps you to confidently tackle the project…or helps you to decide to just hire a good mason. Either way, best of luck to you on your flagstone repair!
We just put in a flagstone patio using decomposed granite in between the stones. Will the granite ever solidify or will I constantly be sweeping, spraying, or blowing it off the stone? It makes me crazy because when it rains or the wind blows, it seems to go everywhere. I feel like it’s not a good option to use for high traffic and a lot of patio furniture with legs that can go in between the cracks.
Cathy,
In 20 years of laying flagstone with stone dust between the joints I have never had this problem.
But when I see this happening on other jobs, it’s always one of two issues, or both:
1. Are your joints too wide?
2. More importantly, are you overfilling your joints? Keep the joint material just shy of the tops of your stones, an eighth inch or quarter inch low–do this, and your problem will be solved. material.
Devin,
I recently purchased a house (last June), and now I have been noticing that the sand between my flagstones is either, sinking, very easy to push down (as if there is a big void under neath the stones or in between the stones), and in some cases small mounds of sand appeared (on top of the stones) with a small crack/hole exposed between the stones. Do you have any ideas of what the cause could be? Or how to deal with it? Do I nned to re-apply screening? I live in Seattle in case that is important. I a, not sure what or how the original owners did the flagstone patio.
Thank you in advanced!!!
First off, thank you for giving your location! I wish everyone would do that. How can I offer landscape advice if I don’t know your climate? So good job.
Sand is generally a poor choice for underneath flagstone. Seee this post here on sand cement or gravel
In short, the sand used is too light of a material and washes away too easily. Worse, ants love it. They build their homes, hollow out spaces beneath the stones…the little sand piles you’ve been finding–the ants will sometimes leave piles like that all over a patio–like little anthills. I imagine they’re not all entrances to the colony, they are just cast-off from their digging.
So my answer involves work. Sorry. All the flagstones should be lifted up, the sand replaced with screenings. Best of luck!
Devin,
First of all, thanks for the fast response. Secondly, never been afraid of a little work!! We suspected that the sand had to be replace or refill/reapply, we just didn’t know what was causing what we were seeing. We were afraid a bigger pest i.e. Voles, moles, or mice were causing the damage. I noticed almost the same effect/thing on the dirt in the garden. I figured this was due to the change in temperature? Worms? Slugs? Ants?
Anyway, thank you for the reference.
Laters
I am happy to help. 🙂
so my first thought was ants….I have never seen rodents leave sand piles atop a flagstone, so I’m still leaning towards ants. Do you have any photos of the little piles? Not that it would prove anything conclusively, you just got me curious.
Greetings! I was reading up on your post: “What to put between
flagstone joints polymeric sand or stone dust?”
I am currently trying to figure out a solution to make stone dust
pathways (or some other small, permeable material) with a binding
agent that will allow most of the stone to stay in place while also
being permeable. I was hoping to create the entire pathway like this
(no flagstones or pavers). I’m really stuck and could use some
advice- What might be the best solution? I have been looking all over-
there is polymer sand, polymer binging agents, etc., but what would
work best for a long path? Location: New England
Hello Elyse 🙂
Best answer: just use gravel. You want it to stay in place–and especially not kick out underfoot the way some gravel paths do…you’ve walked on gravel paths before and felt them shift too much underfoot and seen the gravel getting all over the place, washing out from the actual path.
Now in the above drawing, on the left is 3/4″ to 1″ clean gravel. Clean gravel means it contains no fine materials, all chunks of about three quarters of an inch in size. A path made out of this material will be very loose, and will easily dispersed by foot traffic and weather.
On the right hand side is modified gravel, or d.o.t road base. It consists of 3/4″ gravel mixed with the same screenings that I was speaking of in the article. 1/8″ sized small stone chips and also fine, flour-like dust particles. Just looking at the drawing, you can imagine that the larger chunks of gravel will stand in more sturdy fashion, with the smaller chips packed in tight between them.
And this picture right here, makes it even better. Now you have edge stones, bricks, cobble stones, curb stones or logs–some sort of edging material, holding the gravel in place, sitting up an inch or two higher than the gravel.
Formula I’d use:
1. dig down four inches for the path.
2. Rake it out fairly smooth.
3. Tamp the soil–a hand tamper that you buy at the hardware store will work just fine, a plate compactor will spare you the strain (rob you of a good work-out….I’ll be honest, a very good work-out. Digging and tamping and raking–hard work!)
4. Lay out your edge stones or logs.
5. Spread gravel between them.
6. Tamp the gravel…or not. Maybe lay 2 inches and tamp that, lay the top layer and leave that loose.
This, I believe, answers your need for a walkway where most of the gravel stays in place, yet is still permeable.
I’ve used products before where you actually add a binder to the gravel. These will be an acrylic polymer epoxy resign stuff….essentially, liquid plastic. Stays slightly flexible so “it doesn’t crack” ((yes….it cracks, sometimes)). I was excited by the product at first….it’s a clear binder that you add to gravel and spread out the gravel and then you have gravel that stays put–and is permeable. Huge draw-back is that instead of looking like gravel…it ends up looking like porous black-top. It just doe not look right, does not at all have the look and feel of real gravel.
Still, this stuff is what you are asking me for. It locks gravel together and stays permeable. I can’t recommend a particular company as I’ve only stalled the stuff a couple of times. The stuff I used came in 5 gallon buckets. You fill a wheel barrow full of gravel, add some glue, mix it up with a shovel, dump it into place and rake it out level. Actually, one extra step–they like you to first excavate for your walkway, then lay out this plastic honeycomb material, then fill that honeycomb with clean gravel…it’s a two inch thick honeycomb, then pour 2″ of the gravel glue mix on top of that….so you need to get your excavation fairly level for the honeycomb to sit right….you also need to set an edging material of some kind before you pour the glue gravel stuff–we used two x fours, staked into place, which we removed after the walkway was set, after the glue had hardened.
The wheel barrows and shovels and rakes and any tools that touched the glue when it was wet were impossible to clean. The sales guy who sold the glue mess to the general contractor (yes, I subbed, once upon a time!) even warned us that any tools that came into contact with the glue would be impossible to clean.
I did not want to mention this option–because I do not like it. But, you came to me with a need and I’d rather give you a complete answer.
Minor drawbacks:
1. harder to install–more complicated process.
2. costs more
3. messes up your tools
4. But the real complaint that I have against this gravel glue epoxy whatever we’re talking about, the real complaint is that it just does not look good. Oh and 5. the environment.This stuff is not good for our eco system, our planet, beloved mama earth. It’s liquid plastic, alright. There’s environmental impact happening.
Ahoy, but I do see one application for this gravel glue mess–as a back-top alternative. And that is exactly what it looks like–like asphalt, like black top. The thing is, you mix up gravel with a glue and you get this gravel soup and you dump it into place and rake it out and it slumps down nice and smooth. It looses it’s gravel texture, it just ceases to be gravel….looking like a cross between a rice crispy teat and black-top–but looking nothing like a gravel walkway.
Good luck, with whatever you choose!
The first option that I gave will not keep 100 percent of the gravel in place–but most of it, yes–and if you remember to use modified gravel, gravel with smaller chips and stone dust in it, then it should feel pretty sturdy underfoot.
Hello: I just read your article regarding polymeric sand use, thank you for your thoughts on this. I just completed a four month long project laying 800 sf of irregular Pennsylvania Blue flagstone (variable thickness stone of 1.5 to 2.25 inches think); at our house in Seattle, WA. Joints are all tight at and average of about 1/2 to 3/4 inch in width. I dry laid the flagstone (on a 4-inch compacted base of 5/8th minus gravel with a 1 inch layer of 1/4 minus gravel that the stone was set on top of). I researched the heck out of polymeric sand, and tested out three different kinds. I really liked the overall performance of Techniseal HP2 Polymetric sand; so I went with this as the final selection. I was very worried about the hazing of the stone from using Polymetric sand. Therefore I very carefully applied the poly sand directly into the joints using a grout bag. I filled each joint half full and then ran a light plate compactor (with rubber protector matt between the plate and the stone – this vibrated the sand down into all the voids at the bottom of each joint) then I came back through with the grout bag and filled the joint to the approximately 1/8th of an inch below the top surface of the flagstone. I then took a blower and carefully blew away the very small amount of dust that accumulated on the open surface of the flagstone as a result of the vibrating process. Then I carefully used light spraying of water over the joints ensuring they were fully saturated to the full depth of the joint. Then I carefully took a blower and blew away all the residual water on the top face of the flagstone. I have completed about 25% of the 800 sf of patio and walkway via this method. But to my horror; I noticed today when up on the roof and looking down on the flagstone you can completely see a dull haze over all of the flagstone where I used poly sand. It was wet out today and all the beautiful color of the flagstone was showing nicely where I have not used poly sand on the joints; but in the areas where I used poly sand it all has a dull haze and the natural colors just don’t come through. Its looks like a flat matte color where there was poly sand and where no poly sand you see a beautiful high gloss high color finish…….this is the best analogy I can think of. I have a great photo showing this that I will email you separately. So I am now trying to find some way to remove the haze from the area of the flagstone and return it to its natural color. Have you had any luck, or heard of any way to do this? Do you know if one can expect the haze to slowly fade away over time? So far we have tried aggressive scrubbing test areas with soap and water, aggressive scrubbing with a 50/50 bleach mixture, and also with a powerful house siding cleaning mixture……all with no luck, the same haze remains. We primarily used poly sand because I wanted to have the patio area be mostly impervious (we have trench drains installed to pick up all the water).
Wow, that’s frustrating. And you were obviously very meticulous too. Anyway, sorry to hear of your troubles.
Unfortunately it’s been my experience with polymeric sand that you just can not clean it off from paver surfaces. There’s no type of soap that will help, wirebrush does nothing at all. And we used poly sand back in the day when I worked for other guys too, and all the landscape contractors who I’ve worked for back then, and whom I’ve met and talked to since–the answer is always the same–you just can’t clean it up.
Well obviously that’s absurd. There’s some way to clean the stuff of your flagstones! Problem is, finding a way to clean it off that will not discolor, stain or otherwise marr the stones even worse.
First of all know that at this point, any means to clean off the stones will likely destroy the joints that you’ve installed. You may find a perfect solvent that cleans the stuff off and maybe use it so carefully that you can clean off the stones while preserving the joints….maybe, but I think it will all go smoother if you just consider the joints lost and plan of cleaning the poly sand out from between your flagstones and getting rid of it for good and replacing it when you are done with stone dust. Or 1/4 inch minus gravel–of all the synonyms used so far in this article and in the comments, you’re the first to bring up “1/4″ minus gravel”. Must be a west coast thing. …from what I’m able to google on the matter, I’m pretty sure 1/4 inch minus is graded properly to be used as a joint material. Anyway.
Orange oil. D-limonene. There’s household cleaners out there, they sell them at the big box stores, probably grocery stores too maybe idk, but it’s a citrus extract and you have to be careful when cleaning with it because it dissolves some types of plastic. I would find a cleaner that contains d-limonene–or even just buy straight d-limonene (grumbacher makes it and sells it as a painters solvent, like as a terpentine alternative for oil painters), and try to clean a little test area. “test area” because it may stain the flagstones too.
But yeah, I’d try and d-limonene it, maybe try a “careful” pass with a pressure washer….(a careful pass with the pressure washer shouldn’t damage the stones.)…and get as many of them clean as possible, knowing that a few of them you may have to replace, a few maybe get turned upside down and re-puzzled in to the project, maybe leave one stone still with the haze, as part of the patio forever, to always remind you of this fun adventure.
Once the flagstones have all been cleaned and/or replaced, then return that polymeric sand, buy some stone dust….and send me photos of the completed job when you are done! btw, the photo you emailed me looks GREAT. Very stylistic and attractive stone fitting, very beautiful and interesting contours–I know it’s a bummer having to re-do some of your work, but this patio is going to be amazing, and real soon too.
good luck and let me know how it goes–maybe you can teach me something on the subject 🙂
Hi Devin, your blog on polymeric sand was very helpful. Can you help me understand the difference between decomposed granite and screenings? There’s also some mention of stabilized decomposed granite. Is this just added polymer binder (plastic)? thanks, Chris (Santa Cruz Ca)
Hello Chris. Screenings are crushed stone. The smallest grade of gravel generally available, consisting of small 1/8″ or less chips of stone and fine stone dust, like powder.
Decomposed granite is crushed granite. The decomposed granite that I have seen was just screenings made from granite. Perfect for use in between flagstones.
I can’t say too much about stabilized decomposed granite. Sorry, never used it! I understand that stabilized granite actually predates polymeric sand and that there is such thing as stabilized decomposed granite made with *psyllium husks, but that the term “stabilized decomposed granite” can refer to DG stabilized with various binders.
Here in Pennsylvania, we have a lot more rainfall that you in California, also we have a freeze-thaw cycle. Despite that, regular stone dust usually works just fine in between flagstones, without any binder, polymeric or otherwise. DG will work the same.
I hope that helps!
*it’s a plant fiber. You may be familiar with it as a stomach medicine.
I am in South Texas and am planning a new backyard pool installation. We want to go with a flagstone patio around the pool. I had planned to use decomposed granite for bedding and also in the joints. My concern is two fold. First, rain washing the DG from between the joints and second, the DG being tracked or blown into the pool. In your opinion, should I use poly sand instead of DG or possibly just pour concrete? Also can I expect your comment via email or simply on this site?
Properly installed, rain washing the decomposed granite out from in between the flagstones should not be a problem.
Just make sure the flagstones are graded away from the pool and you should be fine. Keep your flagstone joints less than 2 inches wide.
To keep the decomposed granite out of the pool, my biggest piece of advice is to take time during installation. Sweep the dg into the flagstone joints, then carefully hose it down–washing small bits of dg down into any voids that may be hidden underneath the flagstone. Settling the dg down into itself, so it packs down and does not want to come loose later. Then, letting the patio air dry–and repeating. Sweeping dg into the joints again, because some voids will have appeared after the first hose down, then hosing down again. If you take your time with repeated sweepings and hosings, then, when rain does come, the decomposed granite will be set into the joints already and any loose bits will have already come loose.
good luck!
Hi, love the blog, just stumbled into it and you have a great skill at explaining things. I was looking for an explanation of “red dust”. I am sure this is what the person who installed our flagstone patio 8 years ago said to use to fill the cracks. My guess is that this is a type of decomposed granite or screenings? We live in Washington, DC. Am I correct in assuming that I can use this also to level out some stones? Thanks again!
Yes, he was almost certainly talking about screenings. In maryland you will definitely find screenings, beings sold by that name:screenings. Grey stone dust screenings will cost about 40-50 per cubic yard. Red stone dust will be harder to find, and will cost more. I’ve done a few jobs in maryland and the greater D.C area, and that’s what I’ve seen anyway.
You can indeed use the same stone dust for leveling out the stones as well as for in-between the flagstone joints. On occasions when I have wanted red for in-between the flagstones, I’ve just used grey for leveling, and purchased a smaller amount of the red. The red, being more rare, is sometimes available in bagged form, in garden centers, but not in bulk at the mason supply places or quarries (where I usually get my screenings, because as a contractor, I’m usually buying at least a yard.)
I hope that helps. If you do find my advice useful, then please do share some of my work on whatever social media you use, especially photos of my dry stone sculpture:
http://www.devineescapes.com/dry-stone-sculpture/
Best of luck, and happy flagstoning!
Thanks, I added your sculpture to my Facebook timeline – nice work!
One last question on screenings – is this something Home Depot carries? I think I have seen bags of “paver base” or something like that. Is this a different product or same thing but a different name?
thanks again!
Not familiar with that product. Sorry! Any garden center or landscape supply place should have what you are looking for.
If the “paver base” is made up of 1/8″ chips of stone, mixed up with smaller bits, much of which is so small that it is flour-like, then, well, it’s the right stuff.
Your answers to questions were helpful, thank you.
I am happy to help, Helen 🙂
If my flagstone information and hardscape question answering has been useful to you, then please share my website and/or my photos on whatever social media you use.
Thanks
Hi Devin,
i found your site a few weeks ago, but lost a hard drive and all my history–so thankfully found you again 4 days before i start an irregular flagstone project (mixed pieces of Mtn Mist and Blue Ridge, unfortunately not as sizeable as the examples i see in blogs. Great work, you’ve inspired another.
Here’s the quick story: I’ve reclaimed enough of the small pieces from borders created by the previous owner.
they were sagging, and needed to be re-done, so why not try to re-purpose them into a patio for our growing family.
&When i say irregular, i mean irregular. Some pieces are 2″ thick x 12″ long by 4″ wide…some are 3/4 to 1″ thick 10×10 size,
with only a handful ‘ideal size’ pieces to keep it anchored
together, i suppose. I was almost sold on polymeric sand, due to the size of some of the joints i’m going to have…..but read your blog. I’d prefer to NOT use it…but, i also don’t want my son dragging in’fines’in his shoes and adding more ‘character’ to our inside floors.So, if i go Screenings instead–please let me know if you feel this is
a good materials plan:
225sq.ft @ 4″ fines/3/4″ gravel base…= 5.5 tons of fines/gravel base (Then, if i have stones from 3/4″ – 2″ thick variance…how much do you recommend in screenings for 225 sq.ft?I appreciate all your insight and feedback.
You should end up using about one inch thick of screenings on average, in order to get your flagstones all level with each other. 1 ton of screenings will do about 200 sq at 1 inch.
A little bit more, less than a quarter of a ton for the joints. A ton and a half should work, but buy two tons if you’d rather have extra than have to make a second order. And to account for waste and mistakes.
Make your joints tighter. You can do it. Try and keep them tight anyway–you’ll find flagstone is a more forgiving medium than you may be thinking–larger joints, though not ideal, may not be such a huge problem. The screenings will generally stay put, once they’ve been swept into place and hosed down real well. Polymeric sand, in the case of larger joints…is just even more likely to fail. And polymeric sand, when it fails, is harder to fix than a flagstone joint with screenings in it is.
You can do it 🙂 Good luck
Hi, the home we own in Colorado has a really large flagstone patio but the previous owner never put in any fillers. We thought of ripping the whole thing out and putting stamped concrete because we hate the gaps so much (weeds, ants, etc). Where do you buy the screenings? and do you ask for just that (“Stone dust” or “screenings”)? Do you think this woudl be a better option than concrete with our climate? Thanks! Kristi
I can say without reservation that you should repair the flagstone patio that you have…and never replace it with stamped concrete. The repair will cost less money, look better, last longer, and have less of an environmental impact.
Repair the flagstone. Find someone who specializes in dry laid flagstone work.
Purchase screenings at a landscape supply store or at a quarry. In Colorado, I believe they are sold as “crusher fines”. Everywhere where there’s a quarry, you’ll find this product….perhaps with different local names. Go to a place that sells gravel, sand and mulch and talk to them.
hi, I just finished building a house with permeable driveway. The house is in Los Angeles, California. We have 4″sands as sub grade than we use Belgard permeable pavers that has 1/2″ gap in between, and filled them in with 3/8 gravel. After 4 months, it starts to have wavy driveway. Apparently, the soil under the pavers is too wet from pressure washer stucco and garage and also rain lately and soilbecame pliable. Can I use polymeric sand to fill in the gap or decomposed granite? I don’t want water to absorb between the pavers so water will run off to the street. We have to install the permeable pavers because it was required by the city. Please advise what to do. Thank you.
Sorry, this website is all about natural stone. Flagstone, and such-like. I have no advice nor opinions and nothing at all to say about permeable pavers.
Good luck though 🙂
great article wish I would have read it before installing my pavers. Any idea how to remove the haze from the pavers?
I have heard many hardscapers claim that “it’s impossible to remove the polymeric sand haze”. In reality, nothing is impossible.
A wire-brush plus a lot of elbow grease will often remove much of the haze–will rarely get it all though.
I would look under the sink and see if you have any orange based cleaning products. Anything with d-limonene. If it works, let me know! But d-limonene does dissolve a few types of plastic, so I am thinking that d-limonene with a wire-brush just might do the trick. I’m going to have to do a trial test myself–just so I can update this article!
If you do not have any orange based cleaner, then try using a bit of vinegar along with the wire-brush. Again, elbow grease.
Like I’ve said many times–just stay away from plastic landscape products! Ixnay on the oplypay urethane-ay and-say,okay?
If my advice is at all helpful, then please share my stuff on social media. Tell a friend and stuff. Thank you and good luck 🙂
Hi Devin,
Here’s an application that is somewhat unique, and problematic so far. We enclosed the space under our south facing deck as a sun room, hoping to grow some flowers and/or veggies year round and also have a warm sunny place to hang out for three seasons. We had a pro lay a flagstone floor. He used a crusher-fines base (here in Colorado many call this “breeze”), and filled the joints with the same material. We don’t want to worry about spilled water when gardening, so permeable is good. The joint are fairly wide – 1″ to 2.5″ average, and he even left some 3″-6″ areas along the perimeter walls. He hosed and tamped the joints a couple of times, and I’ve hosed them a couple more times since. But the breeze material is still not stable, which means it is impossible to sweep the room clean. And as it is not outside, we are not getting natural rain/drizzle/snow which might more effectively harden up the joint areas. Actually both sweeping and hosing results in joint material all over the stone surface, and of course the joints then become less level than the stone surface as the breeze gets swept or washed out. I was hoping to find some neat product that we could add to the breeze or mix with it that would make it stable. One web site even suggests a 1/3 dry portland cement/breeze mix, to then be gently soaked with water that would harden up. Would appreciate your thoughts!
The joints are too wide. Keep your flagstone joints tight! Fly me out there and I’ll make em fit nice, get some local ahem pro to do it right or maybe try some ground cover planting. Wide flagstone joints are okay….if you plan on planting say irish moss or clover or something. Portland cement should not be used. It will crack. The other site is wrong.
More on why cement is a terrible option, especially when the rest of the project is dry laid, here
Tighter joints!
Best of luck to you!
Devo, your work is transplendent, I love the ethereal influence of the cosmos in your work how do you go about dry stacking a sphere? Incredible. Best,Aaron
Thank you. the process of building a dry stone sphere, for me, is always a cosmic and transformitive experience. I go about it… with love, gratitude, and hammers, chisels, powertools and with all that I have.
Hi Devin,
Thanks for the amazing article. My husband and I were considering using the polymeric sand in our new flagstone patio but my gut was telling me to go with the natural product. It absolutely does seem counter-intuitive to introduce plastic to a “landscape”; thanks for articulating this so well.
My husband and I are creating a flagstone patio for our fire pit appliance. On impulse, I created a design, using a few large pieces of flagstone, in the centre of the patio. We surrounded the design with the rest of the flagstones in a circle (resulting in a centre medallion type of look) and then they are laid randomly to the outer edge of the patio in a normal fashion. Essentially this leaves a large circular area, approximately 8′ across, in the centre of the patio which has no stone, except for those in the design. We’d like to use a contrasting product to highlight the design and fill in the empty space. I’m hoping you might recommend something. We have bright red Adirondack Chairs. We are in Ontario, Canada. Many thanks!
I’d really have to see what you are working with, what the flagstone looks like–and then it would be a matter of looking into what is available in your area.
If you wanted to email me photos, then I could do some research, and then I could advise you. That would take a bit of my time and consultation fees would be applicable.
consultation work
Perhaps some mix of local materials may work, but it all depends on what materials are available and what color pallet we are working with.
Hi! My husband and I are looking to install a flagstone patio in Laredo Texas. We’re actually fixing a poorly done patio for a friend. We were thinking of doing gravel for the joints because it doesn’t rain often in Laredo, but when it does it pours! So first we plan to dig out and level the area, then lay down some coarse sand (tamp it) for drainage. We were also going to lay a screen to prevent weeds from growing through (I think below the sand, is this right?) and then we would lay down the stone and grout the joints with the gravel. Would this work? Are there any key steps I’m missing?
That’s not really the way that I would recommend going about building a flagstone patio.
This article may be helpful:
http://www.devineescapes.com/flagstone-what-to-use-sand-cement-or-gravel/
Clay base, with about 4″ of 1/4″ clear gravel, followed by 1″ of screening before putting down 20″ X 20″ patio slabs with next to nothing for gaps. Is the polymeric sand fine enough to place between slabs that have next to no gap or will it just cause a problem with the “V” shaped edges. Is there a liquid or possible caulking that could be used in this type of situation?
Thanks for any help….
I do not recommend poly sand. Nor would I use any sort of caulk.
First choice: Stone dust.
Too tight? Sand.
Polymeric sand is no good. That’s kind of the main thesis of this article: do not use that stuff.
Thank you
Hello, could you please post a few close up pictures of the stone screenings that you use so we can try to match our locally available products as closely as possible. I am filling 1/2″ – 3/4″ joints in flagstone.
I suppose I could…but I just did a google image search and the results look right to me.
Stone screenings will contain 1/8 inch to 1/16th inch small chips of stone, like large sized sand, and fines, which will be like flour.
And thank you for bringing me 1/2″ to 3/4″ stone joints. Everyday of my life, there’s someone asking me what to do about their 8 inch wide flagstone joints. And the answer is always–make them flagstones fit tighter!
Anyways, good luck!
Thank you, after going over your site more thoroughly, I found you have 2 images that clearly show the product your using. I selected Galleries and then Flagstone Walkways, the last two images once magnified to 500% show clear images of your stone screenings. The local product I found looks identical to yours.
Cool, I’m glad that worked out from you–and I’ll use those two flagstone photos, for next time someone asks a similar question.
Dear Devin, Great thread. Where are you in PA? I will check out your website further. My new mason installed flagstone using polymeric sand. I had heard it was okay but am now sorry I did not check further. It is washing out. Can I sweep stone dust into the cracks now instead of sand? I realize it would be better to remove everything but I’m not up to doing that. The base is stone dust, by the way, not sand. He only swept sand in between the cracks.
Effort PA. Southern Poconos. Remove all the polymeric sand from in between the flagstones–get it all out of there. Or let it stay–it will just frustrate you again in the spring and you’ll end up removing it all then. Anyway, after it’s gone just sweep in screeinings and be happy.
Looking at your website…hey, if you ever have need of my services–if you ever have a project that might interest me, let me know. I rarely sub, but your outfit looks alright. Yes, I travel for work.
Good luck with them flagstones.
Devin:
Where can I buy stone dust? I only need a small quantity/bag?
Thank You
Anywhere that sells gravel/sand/mulch, usually. Garden center. Or any
Masonry supply place. Quarries will sell it by the ton or by the yard, but
a masonry supply place will usually let you fill a five-gallon bucket.
And the garden centers will often have 25 pound bags of it for sale.
Hope that helps!
I just used stone dust (screenings) as a leveler and in between stones. We got heavy rain and it’s very wet and now some of the stones move and are sloshing around in the stone dust… there are no pools of water but it’s really soft and the lots of the stones move and almost slosh down when stepped on. What did I do wrong? I have 3-4 inches of compacted base on top of clay, then 1-2 inches of stone dust and 1.5-2 inch thick limestone. Should I just stay off until it dries out?
Hi Devin. First off, thank you for all your posts.
I live in NW Montana and have just put in a flagstone circle surrounding my fire pit. I used the natural dirt to lay and level and pressed the flagstone cracks with the same. Now what? My brother suggested sand?
I would not recommend sand for in between flagstone joints.
I have written an article that discusses whether to use sand, cement or gravel for in between you flagstone joints. And I also offer DIY phone consultations, in case my articles are not enough to help you with your flagstone questions.
As for the flagstone surrounding your firepit…you said you placed the stone in “natural dirt”. By dirt, you must mean “soil”. Soil only becomes “dirt” if it gets somewhere it does not belong. Like on your clothes or something. Soil then, comes in many types: Hummus, sand, silt, clay, gravel. Natural dirt could mean any combinations of these soil types.
As a professional contractor, I generally just purchase road base, gravel, and compact it for my foundation. Using your own native soils though, a person COULD screen there topsoil and collect all gravels of certain sized, and mix them with finer sand and clay particles, and thereby create a decent soil foundation, using just what you have.
In fact, I’ve seen many hardscapes– home owner installations, where “natural dirt”, I mean local soil, was used for the foundation. Clay subsoil can compact and sometimes stay fairly stable–but usually, it will settle and heave over the years, sometimes leaving you a fairly level patio, just with a bit of character. Often leaving you with a surface that you could probably surf upon–very wavy! I’ve seen this both here in eastern Pennsylvania and out where you live. Montana and Pennsylvania both have serious winters, that cause soils to heave and settle. The reason for a well compacted foundation of road base or something similar is this–road base can be compacted and yet remains well draining. As such, it handles the Pennsylvania free-thaw rather well.
Anyways–since you just used local soil, and built it yourself rather than hiring a mason, we can pretty much just say “Well, it may not be perfect, but it’s got heart!”. And just fill the joints wit local soil. Encourage moss to grow there. Or plan a ground cover of some type. Even grass seed maybe. Having not seen the patio in question, I really can’t say what is best. But sand won’t help and if you do not want to do it “proper” to begin with–then what you already have is probably fine. Though it may require some maintenance, down the road.
Good luck with your flagstone patio and fire circle then 🙂
Hey Devin,
I live in Texas with the soil is mixed clay and moves a lot. I already clear out a 15 X 15 for my back patio. I plan to do a flagstone patio. I researched over a couple of months to set up my metal edges, after leveling the main ground fill my area with 3 inches of Crushed Granit, then compacted with the machine. I was told to lay my flag stone like a puzzle with a 3/4 in space in between, and use a mallet to get the flagstones to be level with one an other. Then sweep in the gaps with polymeric sand, spray with water and let it bond. Do you have any recommendations on my project?
Do not use polymeric sand with flagstone. Pleas re-read the above article, for my thoughts on that! To lay your flagstone patio 1) set out yours tones like a puzzle, as you said. And with a 3/4″ gap between the flagstones, like you said. 2) level out the stones, one at a time, using the crushed stone to raise them up, as needed. Use the mallet only to gently set the stones into the crushed granite. The mallet can only do minor adjustments, as far as leveling flagstones is concerned. Fill the joints with stone dust/aka screenings, decomposed granite, ect–the same stuff you should use to level the stones out with. Sweep the stone dust into the flagstone joints, hose down to set in place.
Read the rest of my how-to articles, if you have any other questions! If you want individual advice beyond that, I also offer phone consultations! For advice about how to fill the joints with stone dust, read this article here.
Good luck!
Devin,
Thanks for sharing your opinions, works and thoughtful ideas with out natural scales stone patio public.
I have in place 30 year old clay brick patios and walkways. These surfaces are stable. The bricks are on now stable 1-2″ “dry” sand beds. Sand was also used in between bricks as 1/8 ” gap fill. We probably have a dozen small ant hills to show as proof- lol.
My wife and I are interested in a new brown wave patio. We probably will use large pre cut 2x3ft, 2x2ft and 2×1.5ft rectangular size stones. For the most part the patio is sunken 1 inch compared to the barrier strip. Do you think I can drop level on top of the brick 1 to 1 1/2 inches of screening as base, then lay these patio stones on top? I would then proceed to use screening in between joints. I am pretty sure bluestone screening is available in my area.
The walkway to my front door is about 50 feet long but rises about 6-7 feet over about nine 7 inch high steps. The steps are currently on cinderblocks. I intend to lay one 12″ x 5′ long 2 inch thick tread on top of the cinder block. There is no cement now. Do you think I should cement the tread on top of the cement riser? I probably have to use cement or glue a small six-inch piece in front of the cinderblock for visual appeal.
What are your thoughts?
Thanks again.
So you found out about the ants! I keep telling people, if you put your flagstone on sand, then what you’re doing is inviting ants unto your patio!
Anyway, I like to set flagstone on a foundation of road base, also-known-as 2A/modified gravel.
This is a big project that you are describing.. I’d recommend that you spend some time reading my other DIY flagstone articles. Beyond that, if you want to email me photos and receive personal guidance, I’d be happy to help you.
Hi Devin,
My contractor installed decomposed granite flagstones in our patio and we have been having been having major issues with all the DG coming out between the cracks. We are tracking all the dirt and rocks in the house. Looks like it was not sealed properly. My contractor is out of business so I can’t even get hold of him. What is the best way to get the cracks between the flagstones sealed? Would appreciate your advice.
That depends. The only times that I’ve seen people having trouble keeping stone dust/decomposed granite in their flagstone joints, the flagstone joints were too wide.
Scroll half-way down on this link and find the section with the heading “How to install stone dust in between your flagstones” Sometimes people overfill their joints to begin with, then wonder why they have material spilling out onto the patio–aim to have your flagstone joints filled to about an 8th of an inch lower than the top of your flagstones.
Hi Devin, greetings from colorado. great article. Is there another name for dg/screenings? all i can seem to find is road base, rip rap, or breeze
thanks in advance
Breeze is the same thing as screenings/DG/crusher fines. Good luck with your flagstone project 🙂
Devin, Thank you for this blog and great info. We are getting ready to install a flagstone patio a step down from our front porch. I have been struggling to find information on Breeze vs’ Polymeric Sand to put in the 1′ grout lines. My search for this is not yielding good information. I was planning on Breeze but hear it will be tracked into the house and wash away. All the local supply places are pushing the polymeric sand (gator dust) but the 2 contractors I am considering don’t seem to know much about using it. It is helpful to see you are not a fan of the polymeric sand and the reasons why. Just to confirm, anything called Breeze will be the material you like best and that which you call screenings? And that is your preference?
Thanks so much!
Polymeric sand is no good. Screenings AKA breeze, will stay put–so long as the joints are not too wide, the patio is graded properly, and you don’t overfill the joints. It’s kind of silly but often people have screenings/breeze/DG all over their flagstones for the simple reason that they insisted on filling the joints in between the stones all the way to the tippy top. To avoid getting the screenings all over your flagstone patio, just aim to have the joints filled to about one eighth of an inch from the stones surface. Just shy of the top.
This article might help a bit too: http://www.devineescapes.com/taking-care-of-your-patio/%
Good luck!
Hello Devin, I live in Ottawa, Canada and we have an old flagstone pathway. The stones have large gaps between them and weeds are taking over. We just moved in a year ago.
How should we address this issue? Should we scrape all screening, organic material and weeds? And then simply add screening as you instruct on your website?
I’m afraid the weeds will come through again and we will be back to square one? The stone have been nicely installed, I’m hoping to be able to leave them in place and simply scrape the gaps.
Do we need to remove all the flagstones, then scrape everything and start back?
I addressed the issue of weeds and dry laid flagstone here As it states in the article, personally, weeds between flagstones don’t bother me all that much–and if the weeds really are that bad, then a bit of boiling water will dispatch with them nicely.
Here’s an article about removing and replacing the stone dust in-between your flagstone.
And finally, since this is a site specific question, I’ll remind you that I do offer personal DIY flagstone help.
Good luck with your flagstone project 🙂 I hope that my articles are helpful.
I had a flagstone patio laid 2 years ago. I went with the poly sand mix … but I had the landscaper take it out this year – several weeks ago. I sent him your article about using quarry dust. I had the poly sand removed and the quarry dust filled in … it’s only been a week or so. I have mostly smaller spaces between the stones but there are some areas up to 3″ wide. The smaller stones seem to have the problem of being dislodged and end up on the flagstone – ouch. The stones tend to get lodged on your shoes and are dragged into the house. I know it hasn’t been that long since the quarry dust was placed between the stones and according to what I have read in your comments, the stone/dust will settle down.
What I was wondering was if you could spray a water proofing – like what is used on cement – to settle the dust and smaller stones down and and keep them in place. Have you seen this water proofing used before to settle the quarry dust?
Also – do you use stone enhancer to intensify the color of the flag stone?
I’m not a big fan of sealing flagstone or color enhancers. Not a big fan of waterproofing goop being sprayed into stone screenings either. Just hose the patio down real well. Use a leaf blower on a low setting to remove small bits of screenings that haven’t settled all the way in yet. Back and forth–sweep in, hose down, leaf blower…
I recommend that you check out this article as well: patio maintenance
Good luck!
Hello Devin, thank you for the very informative article. It just dissuaded me from polymeric sand. I’ll Probably go with your suggestion of screenings or DG. Maybe because it’s quick, easy, and the best practical solotion. Now practical not always my middle name, I was thinking creativity. Have you ever done the cracks in a more creative artistic way? Bear with me here I don’t know a lot about it but have you ever thought about using glass marbles, crushed glass, fish tank gravel in a more vibrant color something that would be a little more creative? I’d love to find something natural in a deep blu to go with the bluestone. I’d love to hear your ideas of anything you think might work. I’m just kind of not liking going with the plain gray. Your thoughts please? Btw I am also in NEPA. Thanks for your input and letting me pick your creative experienced brain!
Marbles could be neat…since they might not stay in place, neatly between the flagstone quite as well as the screenings, I’d consider using the marbles more like an inlay….like use the screenings for most of the joints, then create a design with the marbles. Like a branching sort of design or meandering stream-like pattern.
In bucks county you can get red screenings…blooming glen quarry, outside of Quakertown. White/cream color us also available at some masonry supply places.
Good luck! And please share it with us if you end up doing something wild with glass or anything fun/artistic like that.
Thank you Devin! If things settle down I sure will try something fun! Thanks for your vet insightful information! Wish I’d have found you 10 years ago I’d have you building my dream stacked wall.
Great article Devin,
We have large slabs of Indiana ledge rock some as big as 30 sf and 4 inch thick around our pool laid with 1/4 inch tolerance laid on sand with sand between the stones sme have shift and opened gaps and tilted
Its impossible to fix without big machines so I am planning just to stabilize it
Screenings the best?
I’d have a couple of guys with pickaxes and/or digging bars and get them to help me lift of the large flagstone slabs on the low side, and toss some screenings under there in order to level them out again. Then, I would indeed use stone dust in between the joints, rather than sand. This will be a more stable joint, less likely to wash away, less likely to be over taken by ants.
Hi
I wish I could afford to hire you! We have an existing flagstone patio which was built on a layer of crushed limestone with the same in between the flagstones. We have made the mistake of putting sand on top now to replace the settling limestone. I like the idea of the screenings but do we now have to remove all of the sand? What if we just remove some and place screenings on top of sand? Truthfully our joints are a bit wider than you suggest. Thank you for your devotion to this subject.
I’d recommend removing most of the sand. Take your time and get out what you can. Just did a repair where the sand in-between and under the flagstones was undermined by and taken over by ants. Having said that, it’s a gamble–sometimes you can lay a few flagstones on sand and not have them taken over by ants….so such a small amount of sand in between your flagstones may not be an issue. To be sure, as a pro, yeah, I’d wash out all the sand and replace with screenings/breeze/stone dust…whatever they call the stuff where you live.
Hi Devin. We live in Ontario and I am almost done with my flagstone landing. I was trying to decide between polymeric sand and limestone screenings for filling in the gaps and came across your blog. I like your views and outlook so poly is out and screenings are in….not very keen on chemicals where the barefoot grandson walks!
I also like your stand on being paid for your knowledge and experience. Basic advice can be free but you worked hard and long to get those skills and knowledge.
I have a full time job and a sheep farm and it is amazing how many people want free food just because I have a farm. I have to explain to them that I don’t just go to the freezer and get food, I actually have expenses, commitments and work that they don’t have and if they want free food, they can go out and buy a farm and do all the work for free!
Good, I’m glad my articles helped you make the right call about polymeric sand 🙂
Offering consultation services has really made things easier on me–I used to get emails, phone calls and even text messages from random people looking for free advice. It was getting ridiculous. Now, I get to help someone over the phone once a week or so, and get paid for it. Plus, I’ll answer short and sweet questions here on my blog, of course.
Good luck with your flagstone project 🙂
Hi Devin,
I’m putting down 1-1 1/4 inch flagstone at our place on an island and we don’t have many things (like screenings available). We do have what is called “shaker sand” which is a combination of sharp sand with some pea gravel mixed in (pea gravel that was smaller than normal and was “screened out” from the normal pea gravel.
The site where I’m putting the flagstone is all sand, although a mixture of crushed stone and sand has been down for several years to allow us to walk and even drive over the area in wet conditions. My thought is to cut that mixture down 3 inches and put 1.5 inches of this “shaker sand” on top as my leveling material.
What do you think?
I think you use what you have available. I’m not worried about your base very much if crushed stone has already sat there for years. Even less worried about it, if your area does not freeze during the winter.
Main problem I see so far is that those are pretty thin flagstones for dry laid. I generally use flagstones 1.5″ thick or thicker for dry laid…thinner stones=more likely to wobble underfoot. A one inch thick stone can be used laid dry–but the more surface area the better. Like 1 and a half feet wide would do it…get all the way down to only one foot wide (surface area) at that thin, and it will wobble.
Hope that helps!
Great article Devin. It was inspiring, insightful, knowledgeable and overall great advice. Your work looks great! Thank you for taking the time to post this for the world to see.
You’re welcome. Glad you found the article useful!
I used baking soda on my patio to kill weeds. Spread it all over and hosed it down into cracks. I haven’t filled yet because i am still adding onto it. I found your article very interesting i was already going to use screenings but was still researching and i came accross this.
Good. And thank you 🙂 Good luck with your flagstone project!
does polymeric come in colors? It is an old flagstone patio and the morter is coming out at between the stones. The flagstone are mainly grey from age. Are there certain colors – light or dark?
I hope not. Please reread the article….and just say no to polymeric sand for your flagstone patio. Stone dust, for the win. Stone dust, all week long my friend. Stone dust, for life.
Polymeric sand is usually available in grey, dark grey, and yellow-grey. Stone dust is usually available in whatever colors if road base type gravel are quarried in your area. Here you can buy grey gravel, red gravel and cream colored gravel….stone dust is available in those very same colors, because stone dust is gravel–just smaller.
And I wish you luck 🙂
Devin, You are absolutely the best source of info concerning flagstone installation. Thanks! I just installed a granite flagstone walkway. 8-12″ of compacted 21AA limestone (well compacted), decomposed granite and then filled the joints with decomposed granite. Should I seal the granite? Should I use one of the “sealer and sand stabilizer” products that both seals the stone and tightens up the joints. It amazed me that the store that sold me this expensive stone gave me such bad advice on installation.
I never recommend sealing flagstone. This can make the stone slippery and change it’s appearance…without providing any benefit. Fine, it probably won’t make it very slippery and probably won’t alter it’s appearance all THAT much. But it still does not offer up any real benefit. The real big problem however here is that it “tightens up the joints”. This is basically putting an acrylic binder, liquid plastic, on top of the joints. In your case, decomposed granite joints. This more or less turns your stone dust into polymeric sand…and you know the risks involved with that. Polymeric sand is basically sand mixed with an acrylic binder. Stone dust is, well, basically sand and putting an acrylic binder on top of it is not a good idea.
The industry standard for flagstone installation these days, is still basically to use the methods, tools and materials used in concrete paver installation and adapt them to natural flagstone. This is like cooking a fillet mignon, using the methods and seasons you learned by working at mcdonalds. Don’t cover that steak in big mac sauce.
We’ve been building an Idaho quartz stone (2.5″ d medium & smaller size flag stones) patio. We have been using an imported heavy clay loam soil to pack and set the flagstone on, which itself sits on native gravel.
The original plan to use the polymeric sand to seal the joints is long jettisoned after reading your blog here and others how it destroys the shine and luster of the native rock.
Each stone has been set and packed by hand (earth first packed by hammer, then stones packed with wood and hammer, sometimes jumping).
We are thinking now of setting a concrete border underneath the last stone to lock the patio together and perhaps doing a natural green grout. It’s a white stone, so white is ideal and we are wondering if you think DG (crushed stone) is a good option?
The location is climate type 9b, Northern California. The Patio is shaded except during the winter. All rain is during the winter months.
Sorry, I was out of town and away from my computer when you posted this question. Only now did I realize that I neglect to answer.
If you are building a dry stone patio then no, I do not recommend using a concrete border. If you’ve already done so, I wouldn’t sweat it too much.
Personally, my preference is to merely lay larger stone along the edge of the patio–have all of your edge flagstones, large. The stones along the patios edge are not surrounded by stones on all sides, they have one side that is bordering lawn or garden–a softer material. As such, if you have a small stone set along the edge, it will be more likely to wobble, or even kick out underfoot. Some people try and solve this problem with plastic edging. Others, with a concrete border. My issue with the concrete border is that the concrete may crack. Also, it is unnecessary. Also, it gives a patio a good appearance, to have all larger stones along the edge. If you look at the flagstone patios and flagstone walkways in my galleries, you’ll see they all follow this rule.
Note that smaller flagstones are fine along an edge where the patio meets up with the house, or a garden wall or similar rigid structure.
I’ve addressed this issue here in another post.
Devin,
Before my enlightenment – my aha! moment – ie; finding this website, we had just completed installation of a flagstone patio upon which the contractor used hundreds of bags of polymeric dust (Gator Dust). After only 2 months the patio has developed a “cavity” probably 12″-18″ deep with an oblong hole in the sand about 6″ long. Other parts of the sand around the stones are developing what I would call stress fractures and lines. Right now I am waiting for the contractor and his crew to show up to “fix” the problem. Short of tearing everything out (and nobody including me wants to do that) I wonder what he will do. What would you do?
This site is a great service. Thanks.
Wait a minute–this cavity is 18 inches deep?
If the gator dust is failing so soon, AND there is such a gigantic cavity forming, one can imagine that there must be something wrong with the gravel foundation beneath the flagstones. Assuming that the foundation is gravel. But whatever the foundation is, it shouldn’t develop such a vast chasm. What I would do is lift up a few stones and observe the foundation. Is it deep enough? Is it well compacted? Is the patio pitched in the right direction, and pitched consistently?
IF they did all of that stuff right, then such a chasm should not have formed. But maybe some minor irregularity of the pitch and/or grading around the patio caused water to heavily move through one area. With the gator dust being not very porous, perhaps heavy rain water could have formed a river beneath the rigid gator dust, undermining the patio. Well, if the foundation and pitch all seem decent, then I’d simply suggest removing the gator dust and replacing with stone dust. Three potential problems remain however a) the flagstones are on sand. Not my favorite option, but not a huge problem so long as b) they fit the stones tight enough. Often, gator dust is used by contractors who set the stones 3 or 4 inches apart, and that usually causes problems. Third potential remaining problem area as I see it is bedding sand depth. If using sand rather than stone dust, then you should try and keep the sand depth to an inch or so. Inch and a half I’ll pass….but if there’s stones with 2 inches or more of sand, then I expect to see more problems down the road.
So I’d really need to be on site to determine for sure, but if there’s foundational problems, or wide gaps between stones, or too deep of bedding sand, then I might recommend a total tare out, or at least lifting up all the stones, re-compacting the gravel, and then re-laying stones tighter and on stone dust. I hope for your sake, and the contractors sake too, that such a fate can be avoided.
Good luck!
Very informative articles. You’re the best source for flagstone info on the net. I’ll probabvly be emailing you soon, to set up a consultation, as we have some questions about cutting, dealing with elevations and drainage issues, just some stuff particular to our project, and it would be good for someone to “hold our hand” walk us through the process, make us feel more confident about what we need to do. Your sculptures are amazing by the way!
Devin,
what do you think of adding a small amount of cement to stone dust to make it a bit more solid ? And if you think this would work, what proportions ?
thanks
Nope, no good. This falls under the “no cement at all in a dry laid patio” rule.
Back when I was starting, in the 90’s, some guys would lay flagstones and sweep in sand that had some ratio of cement in it, into the joints, then hose it all down. Yes, it stops the joint material, sand/stone dust in place, but it hardens up, then cracks up, then you got these broken up pieces of mortar.
I’ve never seen any ratio of cement to stone dust/sand that works. Only time cement is used in the joint material is if the patio has a proper concrete foundation.
Stick to plain stone dust is my advice, and keep the joints tight! Good luck!
Hi Devin
Thanks for all your comments. Have returned to this post many times.
We have a large sandstone flag patio, installed in 2011 by a company that used poly sand in the joints. Most areas are failing, so I plan on filling the gaps with stone dust.
Here in NE Ohio, limestone dust is all that is readily available. I’ve heard and read about some concerns about the limestone breaking down the flag over time, as well as concerns for efflorescence. Further, the stone dust I have seen is just the “flour” part of the DG that you describe using, without any of the 1/8” particles.
Have you ever used limestone stone dust for flag patios, and if so, would you recommend it? Would combining the dust with some finer particulate 1/8” limestone be better?
Thanks so much
George
George,
You’re welcome, I hope my blog posts are helpful. Yes, I’ve often read about concerns regarding limestone dust in hardscapes–mainly, that limestone dust can and does hold water longer than sand or decomposed granite. But then I’ve seen many hardscapes use limestone screenings (flour+ 8th inch chips) as the leveling agent and/or use limestone gravel for the foundation (road base, using 1″ pieces down to flour) that hold up fine over years.
Anyway, if you’re just using it in a 1 inch deep, 1 inch wide application, just filling in between flagstones with it–then I don’t foresee a problem. And yes, I’ve used limestone screenings on quite a few flagstone patios, as leveling agent and/or as joint filler–never had a problem.
But wait, the limestone dust that you have access to is just flour? Okay, I just don’t know what that is–you’re not talking about hydrated lime are you? Bagged stuff, like you’d add to mortar? If so, don’t use it.
I did find “limestone screenings” on this website:
http://www.greenbuilderssupply.net/pr_bulk_materials_dumping.htm
Not sure how far they are from you, but this material looks right. IDK what the “limestone flour only” material is you speak of, but you should be able to find proper screenings/grit/decomposed granite/8th inch minus/crusher run/etc in your area, under one name or another.
Good luck!
Great! Thanks again!
Yes, the material I saw at the quarry very close to my house was just the very fine dust. But I will make sure to get the screenings that include the eighth inch particles as well.
One thing I forgot to ask originally was the issue of freeze-thaw cycle and the potential for the limestone to hold water and then potentially crack the flagstone. Thoughts on that? Perhaps with the larger particles that won’t be an issue?
You’re welcome again 🙂
I’ve used limestone screenings as the joint material for maybe a dozen flagstone patios, over the years. No freeze-thaw issues. Maybe half of those patios also have limestone screenings as the leveling agent–half an inch to inch and a half limestone screenings beneath the flagstones as well as an inch or so on either side of the stones (the joints)–never once have I seen a freeze-thaw issue, or any cracked flagstones on any of these jobs.
See that off-white material between the flagstones? That’s limestone screenings. Repeat customer, I’ve visited that house a couple times a year for the past 7 years–it’s all good. have never once needed to replace a stone, and it’s maybe 800 sq ft flagstone, all told.
Devin, thank you for the article and for your generosity in responding to questions/comments. I live in mid-state NJ and had a 17’x30′ ft. bluestone patio installed over a previously existing concrete patio base. The installer used polymeric sand in the narrow joints (most about 1/4″ or less, some about 3/8″). Naturally it failed. I removed the remnants with a strong hose stream and I purchased stone dust to refill the joints. I can’t find any advice on-line about how to apply the stone dust. Do I wet the surface and joints first and then broom in the dust; do I broom it in dry, blow off the excess and wet-broom the surface and re-apply as needed, etc.? There’s also an adjoining bluestone path with 2″ joints, but I’ve used mulch for those and pounded it in; seems to be holding although it gets weedy of course. Thank you for any comments that you can provide.
Relevant info can be found in this post:
http://www.devineescapes.com/how-to-clean-dry-laid-flagstone/%
Third heading down, “How to install stone dust in between your flagstones”
Basically, sweep the stone dust into the joints, sweep up the excess, hose down on shower setting, repeat.
Essentially
I have had a flagstone patio installed over 10 years ago. I used screenings to fill in between the joints. I have had issues with weeds growing like crazy and for the past few years I have had digger wasps boring holes and burying their eggs in the holes. I have thought of using the polymeric sand to keep out both as much as possible. But after reading your postings I am not sure what to do. What do you suggest or have you had these problems also?
Polymeric sand with Flagstone a bad idea. You can get rid of weeds easily by boiling up a pot of water in the pouring water on them.
If it is a shady area around your patio you could encourage Moss to grow there and let the most take over so weeds can’t grow. I’m not sure what to do about the wasps so much… maybe if you got the Moss firmly established it would stop looking like a good place for the wasps.
Or you could look into planting some sort of ground cover like a creeping thyme or something.
I hope that helps, good luck!
I think I read up above that one shouldn’t have to pressure wash flagstone patios very often – I think you mentioned once every 10 years.
I seem to have to pressure wash mine every year. Some areas actually need it more than once a year…
I live in Connecticut, and parts of my patio and walkways don’t get much sunlight. Some areas are shaded by tress, and some by the house, which I think contributes to algae growth. They get slippery.
I think I also have another issue that I wan to ask about. My patio is quite old – 30 years, or more. Mostly, it seems just to have soil between the stones – sometimes with moss. In a few places where pressure washing has removed the soil, I filled the joints with the rock screening you recommend. I think that where there is soil, the rain results in dirty water covering the stones, making them dirty more quickly than might be expected. Does that sound like a possibility to you?
I have been thinking of taking the pressure washer and blasting out all the soil, and replacing it with screening – i think it will look better, and am hoping it will stay clean longer.
what do you think?
If an area is Shady or damp then sometimes that can cause thin algae growth that can make flagstones look dirty. Or falling matter from nearby trees can help cause that. Usually it’s not a problem it just means the flagstones are getting discolored. If the flagstones are slippery then yeah you might have a more serious issue than that, but usually my clients don’t really opt to feel like they need to pressure wash once a year…
I suppose soil from some of the joints could be leaking out onto the flagstones when it gets real wet and yes that could contribute to the patio looking more dirty although I really can’t say for sure. If the flagstones we’re not getting slippery then I might suggest encouraging the Moss and just living with discolored flagstones and appreciating the Aged look. And your case however what you’re suggesting sounds like a good idea remove the soil replace with stone dust and then watch C if the flagstones don’t get as dirty afterwards.
Hopefully that helps, good luck.
Great article and Q&A’s! i am a fan of screening, but at times, find it hard on bare feet. Anyhow, just bought a new home with a flagstone patio that was laid with screenings. It looks like the guy was pretty lazy/rushed when he laid it as there are numerous 3″ or more spaces everywhere. Suggestions for ‘adding on’? Otherwise, I am forced to walk on hard edged screenings!
Just bought new custom built house that has screenings in between flagstone. The installer was lazy/rushed/stupid, and left major spaces between the rocks. Given how unpleasant it is to walk on screenings with bare feet, what would your suggestion be for spaces that are greater than 3″?
Sorry, I must have missed your question….nearly 2 years ago.
Anyway, I’d re-fit the stones. OR, maybe fit small pieces of stone in, laid upright/on edge. A fragment of flagstone that is 8 inches by 3 inches by 2.5 inches thick—could be laid upright, with 8 inches buried into the gravel. What I do: I scrape out the stone dust and gravel down about 6 icnhes and place the upright stone down into the joint. It’s an 8″ long stone, so now it’s sitting 2″ high. Then I pound that stone down, using a deadblow type mallet.
So there you go: I’m 2 years late responding, but I hooked you up with a secret recipe, which I have used on my more artistic dry laid stone patios: http://www.devineescapes.com/artistic-flagstone-patios/
Devin, Thank you for the excellent article. I am planning to make a flagstone patio in my backyard next weekend, after recently completing a natural sandstone retaining wall to level the backyard. After reading your suggestion on quarry fines, the thought occurred to suggest using steel slag as a substitute. We have worked with a company in Western PA called Harsco Minerals which has a product called Mineral CSA (formerly known as REC MIX) which we have used as a pond liner for treating mine drainage. It is a waste product from the steel making process which is typically landfilled, but it has a beneficial use due to its low porosity and tendency to set up similar to concrete. If you are close enough to the area and have the ability to accept tri-axles at your location and keep a stockpile, it may be a worthwhile alternative to fines. Cheers!
I’d never considered using steel slag for use with flagstone. If you do this, please keep me updated, let me know how it works.
Great article Devin. I was tempted to use the leftover poly sand from our paved project on our flagstones which already have screenings between them because after a good rain lots of stone chips pop up onto the flagstones making it unpleasant to walk on with bare feet. Any ideas?
If stone chips are getting all over the surface of your flagstone, then the joints are probably over filled. What I do is I sweep stone dust/screenings in-between the flagstones, filling the joints until the stone dust is even with the top of the flagstone then I hose it down and off. The water from the hose will cause the screenings to settle–but I’ll also use the hose to wash out any joints where the stone dust remains even with the top of the flagstone because ultimately, what you want is to have the joints filled to about a quarter inch or so from the top of the flagstone. If you leave the stone dust all the way filled to the top, it’s going to spill out and get everywhere.
Hi Devin, I’ve loved to “play with rocks” and recently did some work at our camp on Moosehead Lake (ME). A friend recommended polymeric stone dust so I did a search. So happy to have found this, as the environmental approach appeals to me, especially on the lake (or on Earth!). I used stone dust under as a base and then screened gravel (sand). I have raw edged slate from a slate fall in the woods, so it’s a puzzle to fit, but super relaxing and good exercise. Thanks for telling me the “plastic” approach is lame. I’ll keep trying to keep the fit tight and corners flat. (P.S. I’m 61 and have hauled a TON of this slate. So fun, so tiring!)
Very glad I could help 🙂 One stone at a time, no plastic needed. YES, it’s supposed to be fun and tiring–you’re doing it right!
Very useful information. But what do you do if you need to fix cracking polymeric sand? Are you stuck having someone put more in? Or can you use stone dust to “fix” areas?
Steps to repair cracked polymeric sand:
1. Widen the cracks. An angle grinder or similar tool may be used.
2. Clean off dust and lightly dampen the old cracked polymeric sand.
3. Mix up some new polymeric sand, of matching type and color–mix it up in a 5 gallon bucket, like you might mix up a small batch of mortar. Not too wet–just wet enough to be sticky.
4. Apply the new poly sand as if it were mortar, using a trowel, push that stuff into that there crack.
Results may vary–polymeric sand is not always easy to fix…..
Sometimes it’s better to just remove big chunks and replace with new poly sand–or remove ALL of the polysand and replace with stone dust, or, more polymeric sand if you must.
Hope that helps and I wish you good luck!
Deep bow of thanks for all of the wisdom you’ve shared here with your article and the comment section. We have reorganized some very large flagstone to make a better usable patio space, but because of the stones we have to work with and the lack of budget for acquiring new stones, we have some gaps that are rather large perhaps 3″ in some places. We have “paver sand” i the joints now. Not polymeric, it doesn’t harden. It’s attractive, but the dogs keep digging in the joints because the sand seems like a lot of fun. I was thinking of the polymeric hardening sand before reading your advice here and I’m thinking screenings (Decomposed Granite I think is what it’s listed at in Lowes) might still seem “attractive” to the dogs if it is very loose like sand. They don’t bother our river rocks by the pond but those are fairly large. Would you do a combination something?
Sure, if you have 3″ gaps between your stones you could fill them with a couple of river rocks, and the decomposed on top/around the rive ricks. Or, just fill the gap with road base gravel.
Mr. Devin,
I have a concrete sidewalk that meanders down to a dock by the lake. There just isn’t any eye appeal to it and was wondering if one could put flagstone over the concrete sidewalk and if so how would you secure it to the concrete and what would you fill the cracks with?
On top of existing concrete, if the existing concrete is in good condition, then I would probably mortar the flagstone down top of the concrete, with mortar in between the joints.
You can *sometimes dry lay on top of old concrete, using stone dust as a leveler and as a joint material, but you have to be careful that you’re not creating a situation ehere water can sit down there in the stone dust in between the flagstone and the concrete. As such, I wouldn’t really consider a dry lay option on top of old concrete unless the customer very much wanted it, and unless the flagstone itself were going to have a really tight fitting joints for example if it was going to be a pattern cut, square and rectangular flagstones with minimal joints then, if the walkway is pitched strong enough there really is not much way for a very much in order to get down there in the first place.
Other times I’ve considered dry laying on top of existing concrete because the existing concrete was in bad repair. Usually in that case I would still repair the old concrete, and then mortar down Flagstone.
I hope that helps!
Spot on! I dissuade all of my clients from using polymeric sand. Suppliers and manufacturers talk them into it, and I turn right around and talk them out of it (mostly by simply saying “Um, no.”). This is coming from a guy who originally jumped on the poly sands some fifteen years ago. Like all new things, it takes a minute before you realize the long term results. Just say no to polymeric jointing sand. I thought I was the only one because the rookies and the guys who just want the money sell it like it’s some kind of elixir. Stone dust is the way to go for most professionally installed flagstone patios. Bravo to this article and its author, Devin.
I have two areas to fix. 1. Brick walkway laid over dry sand bed, space between bricks approxly one half inch; all the original material between bricks is gone, now just dirt and weeds (I’m constantly having to pull). 2. Driveway apron of cobblestones, dry laid over solid concrete base; cobbles all shifting around since whatever material originally between is gone. Gaps are approxly one inch. Question: contractors want to use polymeric filler or some combo of filler. Will stone dust/decomposed granite work in both/either area?
They took the quick easy way out–and left large gaps to be filled with sand.
Re-lay on stone dust/pathway fines/DG….they sell it in your area, but since I don’t know your area I can not tell you the local name.
When you re-lay you need to fit them bricks tighter. Yea, buy a few brick, cut them, do it right. Leave small joints, like 1/4″.
Fill with stone dust/DG/screenings.
Do the walk of life.
The cobblestones…..1 inch gap sounds large. Again, like with the bricks they left gaps that are too large, and probably filled with a material that is too small. Solution–fit tighter and fill with larger sized material. Cobblestones were probably laid on a bed of sand on top of that concrete, so it might be best to lift the cobbles, re-lay on stone dust, fit ’em tighter, fill gaps with stone dust.
Do that walk of life again 🙂
I hope that helps.
We had flagstones placed in our outdoor shower about 5 years ago. I’m not sure what was put between them at the time. It’s hardened as sort of a spongy material. There are some areas that need repair. Thoughts on what we could use?
Yea, hardened into something spongey–that’s a polymeric sand type material. I’d remove the polymeric sand and replace with decomposed granite, stone dust, 1/4″ minus/whatever they call it in your area. I’d make the stones fit well first (assuming that the polymeric sand users left big gaps like they usually do), with a half inch (or so) gap between the stones. Just sweep the decomposed granite into the cracks between the stones, then turn on the shower to set the DG/stone dust into place. Good luck!
Excellent advice! Thanks for saving me from the poly sand! On the surface, no pun intended, it seems like a bullet proof option but for my flag stone patio I’m going with the stone dust option! Thanks again for the great advice! Also, very impressive stone sculptures!
Cheers,
Andy
Cool. Glad I could help!
How many inches would you do the compacted aggregate base? I have good sandy loam soil. 2” or 3”? And 1 “ of dg layering level? Thanks! Love the info. Also, no to weed barrier? Also want to do a seat wall in it
It depends on where you live. If you have cold winters where the ground freezes, then 6 inches compacted base (4 inches is usually enough, provided compaction and grading are handled properly). In warmer places, a 3 to 4 inch gravel base is more common. Me, I usually go 6″+ in northern regions, 4″+ in warmer places. Dig down to mineral soil, clay/sand, you don’t want to build on top of organic material. I use approximately an inch or so of stone dust as the leveling agent. Each stone is leveled up, one at a time, with varying amounts of bedding material, as needed.
You’re doing a sitting wall too? This sounds like an ambitious project. Take your time planning….consider taking a workshop if there’s one available in your area…. consider setting up a phone/email consultation with a professional stone hardscape instructor.
I don’t want to discourage you, and I totally think you can do this. But it’s not a small thing. Anyway, there’s many diy articles on this website, which many people have found helpful over the years.
Shoot me an email if you think you’ll need personal guidance, otherwise goodluck and I hope I’ve been helpful 🙂
Devin, Thanks for all your thoughtful advise. I am building and outdoor shower and plan to use natural local stone, which can be fairly thick and irregular on the opposite side of a nice flat sided stone, perfect for a shower floor. I plan on using a thicker layer of concrete sand below the stone, (up to six inches); thick enough so that it accommodates the irregular thickness, and providing me a flat stone surface on top. I then will use the 1/8″ to 1/4″ between the joints as advised. Any corrections or suggestions I should be advised of?
Thanks in advance for your comments.
tj
I wouldn’t use sand, as it’s more likely to settle or wash away. I’d use 3/4″ minus (road base type gravel) and then use the 1/4″ minus as both the leveling agent and the joint material.
Hi devin
I am working on installing a small flagstone walkway with decomposed granite base.
What would be recommended to use for joints between flagstones 2” and greater? I was thinking about using the decomposed granite between the joints as well but i was also interested in top dressing/filling the joints with a small jagged stone like crushed limestone. Which is ideal for large joints?
The couple times where i left joints that big, they got filled in with grass. So idk what to tell you…..then again, over the years I’ve seen a few stone patios with larger gaps, filled with stone dust, and i built a stone walkway once, with large gaps filled with gravel. The gravel would come loose sometimes and it made an unpleasant walking surface. I’d go with the stone dust/decomposed granite. Sure, with such large gaps the stone dust may kick out, and get on the stone surface, but it won’t be an annoyance or a trip hazard, the way that larger gravel probably will.
Hello Devin,
Wanted advice for DIY backyard basketball court of size 42 feet wide and 28 feet long. I have a slope in my backyard for about 15 to 20 degrees. Wanted to check with you the cheapest way to do it under 2K if possible? also can i just use decomposed granite to level and build the basketball court? if yes, how do i make it firm permanently, such that i can have basketball tiles placed on that surface. Also, how could you please help me with All the steps and tools i need to take for this DIY basketball court.
Dig, then tamp, then lay roadbase gravel (3/4″ minus). Screed this gravel, nice and smooth, using a 4′ long wooden level. Hose down. Then tamp. Lay an inch of 1/4″ minus (stone dust, oathway fines, DG) over this, screed out nice and level, hose down ( on the shower setting, don’t soak) then tamp. Will dry up to a fairly hard surface.
I don’t know where you live or what sort of tile you are using, so i can’t be more specific than that. In colder places, dig deeper and have a thicker gravel base, say 6 to 8″, in warmer places 3 to 4″.
At 1200 square feet you’re going to need a triaxle load of gravel….give or take, depending on the required depth. Maybe 6 yardS of 1/4″ minus (decomposed granite is more expensive, just ask for 1/4″ minus, or pathway fines).
600 for the 3/4″ minus
200 for the 1/4″ minus
100 for tamper rental
500 for skid steer rental
Prices will vary….but so long as you’re able to finish while only renting the tools for a day or 2, then you should come in on budget.
The tile company probably makes a rubber underlayment that you’ll want to lay on top of the 1/4″ minus.
Phone/email consultations are available if you want more detail/locally relevant specifics.
Good article, way back then, and still helpful.
What do you think of filling larger spaces with 1/3 portland cement + 2/3 sand, and embedding decorative ‘ornaments’ (e.g., beach stones)?
If there’s a concrete foundation, then sure. Otherwise it will crack up. If you live somewhere with winters, then it will crack up faster. Perhaps you could take a smaller piece of stone, create a mosaic up top of that…and use the resultant piece as a smaller paving stone, set on stone dust, among your dry laid flagstones. Stone would have to be of appropriate thickness, outdoor adhesives/exterior thinset used for the ornaments.
I’m replacing an existing paver patio that was installed on a gravel/stone dust base with flagstones. The existing patio settled in some spots, so i’m planning to regrade it with new stone dust to keep it pitched away from the house. The patio comes off the basement door and is surround on three sides by 4-5′ retaining walls, and had a 4″ drain in the pave patio…it was sinking especially around the drain.
Do you have any comments on how to best drain this so it doesn’t continue to settle after i install the flagstones? Will water flow over the flagstones to the drain with dry set stones, or do i need to do something totally different?
I don’t know what type of drain they installed….or what they did wrong.
Surrounded by retaining walls…so the patio is below grade, and a drain of some type is necessary.
Well yes, if a flagstone patio is pitched properly then water will flow over the flagstones and into a drain. Maybe a channel drain, along the wall furthest from the house?
So IDK, rip out that old drain, and install your new drain correctly. Google “patio floor drain” choose a decent looking one, read their instructions….I’m available for consultations if you wish for individualized guidance on this project.
Hey! I just want to say thank you for your articles and all the questions you’ve answered on here. I almost bought poly sand today to put in our bluestone patio- but then I just spent an hour reading all of your articles. I am Gonna use the bluestone dust we got from the quarry. Thanks!
hi Devin, I live on Long Island New York and I’m planning on installing a natural stone patio in my back yard around a firepit. I’ve seen people do this where the joints were significantly larger than the size which you described as acceptable. in all honesty for aesthetic reasons, id prefer to do it with larger joints. I was wondering if you know the best way to do this and what would be good to use in wider joints. Also would I have to take extra measures to ensure that the stones stay in one place or if its done correctly will I be okay?
You can use stone dust in wider joints….I’ve done so, once or twice and whereas I wasn’t super happy about the way it looked, it did end up functioning well.
Here’s a patio, where for most of it, I set the flagstones maybe an inch to an inch and a half apart–so that’s already wider than usual, for me–but then, for the section of patio just past the deck and surrounding the pond, we set the flagstones more like 2 inches apart. This was done to lower costs, and because the pond area wouldn’t receive heavy foot traffic (so we weren’t worrying about people kicking the stone dust out with their shoes) and also because we wanted a looser look, around the pond.
https://www.devineescapes.com/wp-content/uploads/2014/03/zzz.jpg
Stones will stay in place if done correctly. Don’t use any real small stones.
Stone dust getting kicked out of the joints may be a bit of a concern……but I would fill with stone dust, hose down, and then top it off. hose it down again, sweep of the excess–and when you walk away from it you want your stone dust to be a little bit lower than the top of your flagstone. The flagstones probably aren’t perfectly smooth on top and so it’s basically impossible to get the stone dust flush with the top of the stones anyway, so go an 1/8″ to a 1/4″ shy of the top.
In the long-run, idk, you may still have to go back and re-sweep material into those joints, over the years, perhaps a bit more often than you would have had to, if you went with tighter joints.
Pretty much all of my DIY consultation customers complete their patios, with the final product having much wider joints than I usually allow…and then, out in california it’s popular to build entire walkways using nothing but stone dust. Rake it out, hose it down, let it dry–then walk on it. So I think you can get away with a 2″ joint, if that’s what you’re into.
Then there’s the flagstone work we did around this pond….so loose, I can’t even call it a “patio”:
https://www.devineescapes.com/wp-content/uploads/2015/01/pond-water-feature.jpg
Here, joints were intentionally left 4″ to 8″ wide–and the space between them was filled with sod.
I live in the the finger lakes region of New York. We have large four inch thick, Colonial stone laid on a dry base, like a stepping stone path. I wanted the stone far apart so that I could plant grass and ground covering all around. Do I start with stone dust and then add a top layer of topsoil? Or can I fill all of the stones with top soil? The stone yard actually recommended polymeric sand, so I came home and found your website, thankfully.
You could do it either way, especially since you said these are stepping stones…for stepping stones, i usually just use soil. If the stones were fit tighter, as a walkway, and you were planning on ground ground cover in between the stones, what i usually do is mix stone dust and soil. Most anything you’d want to plant in between flagstones will grow in a 50/50 soil/stone dust mix. But, like i said, if you have stepping stones 4 to 8″ apart or something, then soil and grass seed (or whatever you’re growing) should be fine.
So glad I found your blog, almost as much as finding a buried 12×20 flagstone patio in our backyard! We bought an older house last year, and what I thought was a small stone landing at the base of the old deck turned out to be an irregular limestone patio. We’re expanding the deck so we’re going to rescue the patio and relocate it. I’m glad I read this and plan to steer well clear of polymeric sand. I have used it quite successfully in the past, albeit with concrete pavers; the haze isn’t as bothersome and didn’t seem to last. Anyway, I would like some advice on how you achieve such tight joints. I’d prefer to avoid power tools and stick with as much a natural look as possible. Do you use cold chisels or is a hammer enough? The stones are fairly thick, 2″-3″…thanks
I use a a hammer. Here is a video demonstration of how i cut flagstone using a rock hammer:
https://youtu.be/ReUc33dx794
Be sure to comment on the video amd let me know how the technique works for you. Thanks!
*also note that i do indeed also use a 4.5″ grinder and/or a 14″ saw, in order to achieve a tight-fit patio. Any saw cuts i then rough up, using the same hammer technique as in the video, in order to keep it natural loooking
Try
https://www.envirobond.com/professional/envirosand/
Organic binding material.
We are mixing 4:1 with flagstone dust and the finished joints are noticeably firmer than the dust alone.
Wow – thanks for those great articles! Wish I could hire you to redo my patio in New Mexico! Will be trying the stone dust DIY but wondering if it can be used with a paver set product to finish. Thanks, JoAn
If the project is large enough to catch my interest financially, or artistically interesting–fly me out! I just need big money plus artistic license/free reign!
I do not recommend paver set–it’s basically polymeric sand, and I do not like polymeric sand with flagstone.
Best of luck to you 🙂
Unfortunately, job is small and nothing artistic about it. Thank you for the advice tho! It is also nice to know you are willing to travel if I have a job in the future that meets your criteria! Thank you again and Best Regards!
Great information and helpful blog!
I have a dry laid flagstone patio in the backyard, and am exploring some joint filler options. The joints average about 4-5 inches (way higher than your recommendation) and its too late to reduce the joint spacing, since they have already been laid. Do you recommend using cement/sand mortar combination or to go with stone dust. Would prefer to be able to pressure wash is once in a while, so does stone dust make it impossible to pressure wash them?
You never want to use mortar, if the foundation is dry laid. Stone dust will work. Sweep in, hose down on shower setting, repeat….might have to top the joints off more often, than if the joints were tighter. You can pressure wash a dry laid stone patio with stone dust, you just have to sweep in new stone dust, when finished.
Hey Devin- I too want to thank you for promoting not putting plastic into the environment! My husband who is a builder always goes to the “product”, which i always talk him out of, but cement is one that I can’t seem to stop him from. He wants to lay a new flagstone patio on top of a mix of sand mixed with cement(about 6 to 1). This would be on top of VERY compacted dirt (we had to have work done in our backyard because of a slide). Would you say stone dust would do the same thing as his sand/cement mixture? (stabilizing the bed to lay on?) I am totally on board with between the cracks, but should I insist on the bed as well?
Absolutely. In fact….whereas I am opposed to using cement in the joints, especially if there is no concrete foundation–i can at least see a reason to use cement there: trying to avoid weeds, and looking for a stable joint. It would fail, but I see the reason.
But on a dirt foundation, to set flagstones in a bed of cement based mortar, just doesn’t make sense, for use with flagstone. Are the stones too small, I mean, maybe he’s thinking to “glue” the stones down with the cement? But the mortar beneath the stones will likely crack, making wobbly stones sitting on cracked hard cement. Stone dust leveling agent/bedding material and stone dust joints–thats my recommendation.
*If you are in a place that never gets below freezing, then these recommendations are less crucial. In a northern climate, cement misused in a dry laid application will almost certainly fail. But I’ve seen em fail down south, and out south west, too.
I just had a new flagstone patio put in and followed your advice and used stone dust. Do you have any thought on how to make the surface more solid so particles do not get blown or washed out? Is that just the nature of stone dust? I’ve seen stone dust joint stabilizers are being sold, but that might be as bad as poly sand.
Hose the joints down, on shower setting, sweep off the excess, if you want you can use blower to remove more excess stone dust. You want to leave the joints approximately 1/8″ to 1/4″ below the top of the stone.
More info:
Taking care of your stone patio
“A flagstone patios joints can never be truly “flush with the top of the stone”. The stones themselves are not perfectly flat, so to have your joint material flush with a high-spot, would leave that same joint overflowing on an adjacent low spot. Early in my flagstone patio career I used to try and keep the screenings in my flagstone joints as close to level with the stones as possible, but with foot traffic, wind and rain, the joints seem to naturally level off to around an average of one eighth of an inch shy of flush with the flagstone.”
* This works better with tight joints. You may get away with 2 or 4 inch joints…but it will work better with stones fit more tightly than that.
Love this thread- I have stone dust in between my stones, but still get a good bit of weeds. Any suggestions? Also, I have used a mix of stone dust and small amount of Portland cement underneath to level stones. is this a bad practice?
Boil a pot of water, to kill weeds. I wouldn’t bother with the cement… What you’re describing probably isn’t causing harm, but
stone dust alone will do the job so why add cement?
Devin,
I’m looking to refill gaps in a flagstone patio that are pretty larger — ranging form 1/2 to 2 inches. Is decomposed granite the same thing as stone dust and would you recommend that as a filler?
Thanks,
Mike
Decomposed granite is the same thing. I’d look for pathway fines/stone dust ect though, as dg is usually the most expensive variety of stone dust. And yes, I do prefer tighter joints, but dg should work for 2″ joints.
Hi Devin,
I am a contractor working on a large home renovation project in Northern California. We have a large concrete patio(800 sq ft?) which probably dates to when the house was built(1968). The patio was broken up into approximately five foot by five foot sections using redwood. It appears that they ripped 2″x 6″ in half so that they had 1.5″x 2-3/4″ material. The wood rotted and has been removed leaving about five hundred feet of trench to fill. The slab is about four inches thick so concrete ran under the wood dividers and there is an irregular floor to my “trenches”. They also connected the various sections with #4 re-bar so the patio is pretty stable as one piece. Would love to find a sub-contractor to just do the work but two months of trying hasn’t produced anyone. Am thinking that doing this with decomposed granite is something that I could pay my fireman son to do in his off days. Does this sound like an acceptable solution? The stone dust would just be compacted by wetting and drying? Material cost is more or less of no importance so if decomposed granite would work better or look better than other stone dust I would use it. Thanks for your help, George
Stone dust/decomposed granite would work well in the dry months, but in North California’s rainy season…..I’m just concerned that the trenches have concrete at the bottom, so the stone dust would have no way to dry out, for months at a time. I’m thinking you could take a concrete saw and just run one cut down the middle of the trench. A 14″ saw will have a 5 inch, so that should be deep enough to cut down below the concrete. Then, if filled with stone dust or d/g (interchangeable, I don’t know of any reason why DG might work better) the cut that you made will allow water to drain. I’d use the saw, rather than a drill, because with the saw you can make it continuous, getting the whole thing to drain and would probably be fast to do…but I suppose you could drill one hole every 10″ or something like that.
Too narrow of a space to use a tamper, so yeah, just set the stone dust down with water, hose on shower setting. Expect to be topping off the stone dust trenches a couple times a year, first year or 2. Okay, on second thought……I might hose down really well, then take a 2×4 and a 3 pound hammer to it. Lay the 2x down on top of the trench and hammer down to tamp. Then top off with extra stone dust, hose down, etc.
And really……maybe make the drainage saw-cut, then fill in a couple inches with road base type gravel. Then the top inch or 2 with the stone dust. The larger material will help to jam up the drainage-cut, making it so less fines settle down below the concrete, while still letting water drain.
I had Arizona Flagstone Rose laid as a patio with 1/2″ spacing. The contractor used a Portland lime & sand mortar beige color by Spec Mix between the stones. Some of the stones now have a haze on them. What is the best method of removing this haze safely? There was a language barrier with the installers, they were from Brazil. They laid it out very beautifully and was pleased with their work.
I appreciate your guidance.
Best way that I’ve found to remove that sort of haze is to just use a power washer. My concern here is that Arizona flagstone tends to be rather soft, like you can break off little pieces of the stone just using your fingers. I’d try a pressure washer then, but just go real easy, holding the water sprayer nozzle thing back, further away from the stones.
If the patio is dry laid, on a sand/gravel or stone dust foundation…..then there’s should not be anything portland cement based in the joints. So, if that patio is dry laid, then I would remove the material from the joints at the same time I was pressure washing the stone’s surface. I’d just power wash the whole thing…., some joint material may bust loose just from the water.Then I’d take a large flathead screwdriver and start prying out joint material. Hammer and chisel and/or angle grinder may be needed….but for a dry laid patio just with mortar in the joints, a flathead screwdriver will often be all that you need.
Then, I’d fill the joints in with stone dust….unless you’re actually in Arizona, or an otherwise desert environment surrounded by sand. In that case–I’d just use sand.
Good luck and I hope that helps 🙂
Hi Devin,
Really helpful articles on flagstone. I’m in Tucson AZ and have a very large flagstone
patio that is 15 yrs old and is showing many cracks in the mortar grout. Looks like
the flagstone was set in a concrete base. All the flagstone is stable and still level.
Should I try to hammer drill the mortar grout out? What do you recommend for replacing
the grout? Not sure DG would drain properly with the cement base. Our monsoon rains also might wash it out. Is there a means to just patch the cracks? Removing the grout is
going to be a horrendous job. Thanks for any help you can provide.
If your patio is built upon a concrete foundation then you want to repair the joints with mortar. The article above addresses flagstone joints in a dry laid application–with a gravel foundation. You never joint with mortar in a dry laid scenario. Likewise, you never joint with stone dust, sand, poly sand or DG in a wet-laid scenario.
Remove the mortar with an angle grinder and chisel/large flatheat screwdriver. Leave the hammer drill in the shed.
Repoint with Mason’s mortar…grout is for tile work, indoors. Not to be pendantic! The two terms are often used interchangeably, but the two products should not be used interchangeably.
Have written about replacing mortar joints in a couple of articles.
Here’s one
And another
Good luck!
Thank you for your informative article.
We have a large patio of flagstone set with concrete or mortar. It is apparently about 12 yrs old. the concrete is cracking, stones around the edges appear to lifting. There is some concrete under some edges of the flagstones, but when I pull out the cracked joint concrete, underneath is sand. Some joints are huge with tiny stones sort of floating in concrete. Not a good look. Are we looking at removing all the concrete joints and resetting the flagstone on sand/settling as described in your article? It appears that the base is a sand mixture, not concrete.
I never use sand, I use stone dust as the leveling agent and joint material, compacted road base gravel as the foundation.
As described HERE
Just read this article. Good stuff!
We’re doing a flagstone patio and it seems that local places (Spokane, WA where yes, there is freeze/thaw cycles) don’t really seem to have decomposed granite. You’ve also referred to it as “crusher dust”. Does anything on this page (http://highlandls.com/products/) or this page (https://www.landscapeandgarden.com/gravel-decorative-rock) jump out to you as being the product you recommend?
The 2nd link has what they’re calling decomposed granite, but given my calling around locally, I question if that’s the same stuff as what you specify.
Thanks!
The 3/8″ crushed basalt is the right stuff.
https://highlandls.com/product/3-8-crushed-basalt/
It’s 3/8″ in size, and says “with fines”–that’s what you need. Half inch, quarter inch, eighth an inch–any of those would work–so long as they have fines…3/8 is what I usually use, but I work around the country, and sizes/names vary slightly yet every place I’ve been wcarries something like this.
The decomposed granite in the second link also looks right, but it will probably cost more.
Hi Devin. My front walkway and patio stoop are on a concrete base and have a tan mortar between the flagstone joints. I would like to fill the joint of the flagstone patio with decomposed granite so I can match the color somewhat. I can’t find anyone who sells decomposed granite. Lots sell “stone dust” which is grey. Any ideas? I live just north of Philly (19046). Also, I lived in the Poconos for more than 20 years and at one time not far from your town. Thanks I’m advance for your help.
If your stone is on a concrete base, then you want to repair it with mortar, not stone dust. If the foundation is dry laid, repair using dry laid methods/if the foundation is cement based, repair with cementious materials.
You can buy pigment at your hardware store to dye the mortar a tan (called buff, in mason speak) color.
Hi Devin. Thanks for your reply. I didn’t provide enough info. I want to re-fill the joints of my existing dry laid bluestone patio. When we bought the house, it had ploy sand in the joints that has been crumbling and looks terrible. I want to use decomposed granite or a similar natural product, other than sand, that is tan in color instead of grey. I’ve been researching decomposed granite and want to use that but cannot find a place to buy it. Thanks.
Oh–you’re saying the flagstone patio is dry laid and is adjacent to the mortared step and walkway. …and you want to come up with a dry joint, that has the same color. Okay, so I’ve never seen decomposed granite sold anywhere in south eastern PA–and I lived in Montgomery County for years. There’s “white” screenings–which is more a cream/off white color.
White screenings are made from limestone…and crushed limestone has a bad name, in the hardscaping industry, because it tends to hold water. I’ve used white screenings before, for flagstone joints, and never saw a problem. Year and years later, no problem–but then I have seen hardscapes built by other contractors, that used white gravel for the foundation–and seen jobs like that fail. But that was 8″ deep of crushed gravel, not just a 1/2″ joint. Anyway, I suspect white screenings are going to be too white for what you’re trying to match. Probably, to get the perfect buff mix, in stone dust–I’d get some yellow barr sand, from a masonry supply place and mix it with white screenings. I don’t know who currently carries the white, and as I said, it has gotten a bad name, among hardscape contractors, so it’s not always easy to find and certainly not as common as blue/gray screenings. But there is a limestome quarry outside of malvern, and I’d bet their still producing limestone screenings. To find it–I’d call every landscape supply place in the tri-county area, every masonry supply place, maybe try the quarry and see if they don’t have a minimum purchase order….Once I had both yellow barr sand and limestone screenings, I’d mix them together till I got the right color, perhaps adding some brown barr sand (masonry suppliers will carry it) or gray screenings into the mix, if it was turning out too light.
I know, you said you’re not into sand–neither am I, for flagstone joints. But I would toss it together with stone dust, mixing the two, and consider it an acceptable joint material, so lang as it’s at least half stone dust/screenings and so long as it’s mixed fairly well.
Thanks for such a thorough reply. I’ll get on it. Have a great summer.
Hi Devin. I live in Seattle, and I’m installing a flagstone pathway in my lawn. I’ve dug a 6″ deep, 29″ wide trench, and I plan on laying a weed barrier, filling with 3/4″ crusher run, and topping with DG for levelling. Do you think installing a border on the sides of the trench is necessary? And, if so, is there a way to do this so you don’t see the border material for the finished project? Thanks!
First of all, I build flagstone pathways, not DG…
But yes, for a DG path, a border or edge material is generally necessary. Otherwise, the DG gets everywhere. You can’t really hide the edge though–so don’t bother trying to hide it, but go with an edge that you like the look of. A metal edging or pt lumber border will look better than a plastic border….stone can be used. Will take longer to install, but can be made to look real nice.
Cement/Sand mixture mortar left behind a residue and markings on my outdoor patio stone and walkway. Even after several rains and power washing them, it is prevalent. Any idea on how to remove to get the stones back to previous state?
There’s some things I don’t know here….how long ago were the mortar joints done?
Chances are, they used a grout bag and soupy mortar mix….or just tuck pointed with somewhat wet mortar and didn’t clean it up sufficiently while it was wet. In any event, it didn’t get quite cleaned up enough/soon enough.
Based on the photos, it seems they didn’t remove all the mortar, more a partial job?
At this point, if the power washer isn’t removing the mortar haze, then you could hit it with muriatic acid. They’ll sell it in the masonry section at depot/lowes. Read the directions, follow precautions (gloves, mask, glasses).
Scrub the top of the flagstones using diluted muriatic acid, with a shop book. Scrub with the broom a bit–then hose off. Wait for it to dry…or use a leaf blower–then look to see if the haze is gone. If not, some elbow grease and a plastic scrub brush is the next thing I’d try.
Be sure to hose off and don’t let muriatic acid sit long, as it can deteriorate the joint material…muriatic acid eats cement.
Also, I’d wait at least 2 weeks before powerwashing over new joints–and at least that long, more like a month, before using acid.
What do you suggest using in the joints of a Limestone walkway (in NY)? Thanks!
If the stones are set upon a concrete foundation: mortar, as addressed here. If the stones are set upon a gravel foundation: 1/4″ minus.
Hello, I apologize if this has already been answered. I have an Arizona flagstone patio & sidewalk with mortar over concrete pad and live in Colorado. Would you advise just sealing the mortar?
No worries. So you may or may not have seen this article, where I talk about how I do not recommend sealing flagstone. But I get it–you’re suggestion you’d just seal the mortar itself. Take a 1″ paint brush and just apply sealant to the mortar joints, keeping the stone not sealed. The thing is….I don’t think sealing the joints would really help much. I don’t know if it would do any harm though, but it might.
Best thing you can do to extend the life of your patio mortar joints, living in Colorado or any place with harsh winters–is to stay on top of the snow. Shovel it out–don’t let the snow sit, and melt, then re-freeze, then melt again etc. And don’t use salt either. Calcium chloride or other salt substitute should be fine, but salt will deteriorate mortar.
Hello Devin,
I wound up reading your blog post on using poly in flagstone joints. I
love the back and forth in the comments section. Extremely helpful.
Wondering if you might have a quick second to let me know your
thoughts on a recent dilemma.
A customer installed 46 tons (4000 sf) of ½ to ¾ decorative type
stone, fairly rounded with minimal fines on their driveway. The look
is great, however, it is too soft for their liking. I am considering
adding about 5 to
10 tons of fines to firm things up a bit, hoping that the smaller
particles will help lock the larger stones in place.
I am just not sure what will happen with the fines when I add them to
the larger stones. Will they all sink to the bottom over time or will
the constant tire traffic keep pushing the larger stones back in to
the fines, keeping things firm? As it stands now, even a 20%
improvement will satisfy them.
Sincerely,
Rob
Rob,
46 tons spread out over 4,000 square feet…3/4″ material, fairly rounded.
Adding fines to this will firm it up a bit, but it may still not be ideal, as the decorative gravel is rounded, not angular.
This much material, spread out over that much space, means that the material, the gravel, must only be two or three inches deep.
Here’s what I’d do:
1. Add at least 20 tons of fines.
2. Spread it out, rake it in, hose it down. Run a vibrating plate compactor over the entire area.
3. Install another 46 tons of gravel, this time the appropriate 3/4″ minus, angular crushed stone with fines. Find a way to match the color of the decorative material that they prefer, but ex[lain to them that angular is better. Rounded is not going to be very sturdy…because it’s rounded.
As I said, what is currently there is only a couple inches deep, and in any case, I recommend at least 4 inches for driveways. 6 inches if you’re expecting a lot of traffic. 8 inches if any big trucks will be coming through ever. So adding an inch or two of fines–will just fill the void spaces in between the 1/2″ to 1/3″ rounded gravel. Then the additional couple of truckloads of gravel, actual 3/4″ minus, will bring the driveway up to 4 or 5 inches thick.
Hi Devon,
Thank you for your expert advice – make perfect sense!
Will do exactly what you said.
Sincerely,
Rob
You’re welcome Rob, I’m happy I could be helpful 🙂
I know this was posted quite a few years ago, but I’m going to give this question a try. We had a flagstone patio put in last year. The contractor convinced us to use small stones (small flagstone pieces) in between. I was not thrilled with it at the time but time and money influenced our decision. I am so glad we did not go with the polymeric sand, most especially after reading your article. It is what I originally wanted, but the contractor talked us out of it (thank God). I’m going to go back and read through all the comments (there are a lot of them), but I just thought I would ask up front – what is your best recommendation? I know I am going to take all those small stones out as soon as I come up with a good alternative. Most of the patio is in a high sun area, so moss (which I love) is out of the question I think. Thank you very much.
It’s an old article–but it’s been updated recently.
Best recommendation is to use large flagstone, small joints, stone dust/decomposed granite as the leveling agent and joint material. 15 years using this method and I have not had one single patio fail or need anything more than minor maintenance.
This method is described HERE.
You are so kind to answer so quickly and for the method link. I thank you so very much. Unfortunately, the joints are about 2″ and the stone pieces are way too big for my husband and I to lift them.
Thank you again, Devin.
Well I understand that the stones may be too small. 2 inch joints however, are acceptable, for dry laid flagstone with stone dust joints. I prefer to keep them tighter, but 2″ is doable.
What is the best order to correct an incompleted project gone awry? Last year, I installed the landscape fieldstone for a courtyard but after an injury, had to stop before completing. There were two erosion spots that created 4 low spots. (Note: I am not a professional, but love to DYI landscape).
I plan to move every stone out to the opposite side and keep the pattern intact. After that I have one side that I will change to/add retaining wall stone borders to better lock my stones in. Next, I planned to re-do my leveling with sand and a plate compactor, followed by screenings (this hadn’t happened before) & again the plate compactor. Finally, I’ll bring back the stones and level them (with screenings?)
I do think I may need to cut a center trench prior to adding the sand and screening to add a drainage pipe in case of future settling? Your Thoughts are? AM I missing anything? Stone thicknesses range from 1 1/4 – 2 1/4″. I have 4 large, thick stones for the 4 ‘corners’ and many med-large stones interspersed for stability. The rest are med to med-small with a few fillers.
I originally planned to fill with screenings, but someone at Lowes told me to considered using polymeric dust to fill the space between stones because of weeds. After reading your article, I’m confused..
Is polymeric dust the same thing as screening? Are these two similar products? Do you seal your stones after adding the screening? I can’t and dont use Round-up type products, so that’s a plus, but I also want to keep the structure stable and level as lots of kids run through the yard. Thank you for your thoughts and guidance!
DIY flagstone advice from a guy at Lowes…sounds dangerous.
No polymeric sand. En Oh spells nope, just don’t do it, ever. Just don’t!
Never seal grave level exterior stone. Reasons are described
HERE.
Screenings are not the same as polymeric sand. No acrylic, plastic, or polymers are required in your project. You are building a flagstone patio…just use stone. Level the stones following this procedure.
If you purchased plastic edging…..just return it to lowes.
Hello Devin, We found your article a little too late. We’re halfway through a DIY of flagstone on the side of our driveway. We’re using paving sand as the base. Do we start over? Or pull up some layer of sand and put screening in?
We did buy poly sand, but can exchange it for the screening. Just wondering what we should do about the paver sand underneath
You need a foundation of compacted road base gravel.
Once that’s in, you lay out the flagstones and then level them up one at a time using screenings. If you just have sand in….and no road base gravel–then absolutely, take up the flagstone and do it all over. However, if you are telling me that you have 6″ of compacted road base type gravel in place, and your flagstones are on top of that, with some sand as the leveling agent…..then idk, but as a professional who can’t afford to have my reputation messed with–I’d take those flagstones back up and lay in screenings.
Great advice and beautiful work around the pool.. thank you!
I have a flagstone walkway with the stone separated by 3-4 inches (anything closer would be considered an impervious surface and restricted by zoning due to coverage restrictions so nothing to be done about that). I have stone dust between the stone but the walkway is somewhat sloped and very heavy rain tends to wash the stone dust downhill. Any suggestions on how to keep it from washing downhill?
Thanks.
The first thing I want to do is find a way to make it less sloped. Ideally, we’d have a slope of 1/4″ per foot/ 1″ over 4’….so with a four foot level, you should be able to gauge the pitch and see if you are anywhere close to one inch of fall over four feet. With large gaps like that, this is the best that can be done–is find a way to get the slope corrected. If it means re-grading a bit of yard, or installing a step.
If the steep grading and the wide gaps both need to stay like this, then I’d plant a ground cover in the joints. Replace joint material with a mix of topsoil and gravel or stone dust. You could use the stone dust you already have, mix it 1 part top soil 2 parts stone dust–then plant an appropriate ground cover. Irish moss, creeping thyme…idk, what plant would be best for your local conditions. Check out http://www.stepables.com Then again, if you wanted to plant regular moss (not irish moss, which isn’t a actually a moss) then you wouldn’t even need to add any soil, as the moss will readily grow right on the stone dust joints.
Thanks for the quick reply. I will give the dirt/stone dust mix a try next time it washes out. Not much sun on the walkway but I’d imagine moss doesn’t care that much about that.
Hi Devin,
I’m so glad I found your webpage. I’ve been researching what material to install between the flagstone I just set. I’ve created a 15’ x 15’ flagstone patio using 1.5-2.5” mostly flat, some irregular stones. The gaps range from 1/4” – 1” between stones.
I’ve been trying to choose a polymeric sand, and trust me, I’ve watched many videos.
No one seems to be recommending DG or granite sand until you. I’m going to take your advice and fill the gaps with granite sand. I used the granite sand as my leveling layer, too.
One question…would mortar work better than poly sand? Any cons to using mortar?
Thanks again!!
Did you set the flagstones in mortar/on top of a concrete foundation? If so–then fill your joints with mortar.
If you set your flagstones upon a gravel foundation/on a bed of sand or stone dust–then fill your joints with stone dust.
Polymeric sand is not a good option for either sort of foundation.
Thank you for the prompt response. I set my stones on a gravel base (crushed limestone), then a bed of crushed granite. I presume stone dust is finer than crushed granite, yes?
That depends on the supplier. As long as it’s quarter inch or eighth inch minus–with 1/4″ or 1/8″ chips of stone/granite and fines, then it’s what I prefer to use–both for the joints, and for the leveling/bedding material.
Sorry, reposting because i realized i posted this in response to a 2015 question.
I just used stone dust (screenings) as a leveler and in between flagstones. We got really heavy rain and it’s very wet and now some of the stones move and are sloshing around in the stone dust… there are no pools of water but it’s really soft and the lots of the stones move and almost slosh down when stepped on. What did I do wrong? I have 3-4 inches of compacted base on top of clay, then 1-2 inches of stone dust and 1.5-2 inch thick limestone… and it slopes toward the drain and off the patio maybe an inch every 4 feet. Should I just wait until it dries out?
First of all, what? I’ve never heard of anything like that. Mind you, 2″ is kind of thick for a stone dust bed and if you’re joints are on the large side….and if you got an absurd amount of rain….but it still sounds funny to me. I’ve seen many walkways made with only stone dust/decomposed granite. They didn’t just turn to slosh. Seriously, how much rain did you get? An inch of slope per four feet is right, water should flow.
Wait, wait, you’re saying lots of stones move when stepped on. So the stones just didn’t get seated properly. Push down on on the corners of a stone–if the stone goes down, then that corner needs to be lifted and a handful of stone dust tossed under there, then rap it down with the mallet…it sounds like you just need to take your time and wobble -proof your stones, as described in this article
Thanks again! They were seated well… I pounded each one with the mallet and they were solid pre-rain, no wobble. In fairness, we got a LOT of rain… almost a foot in a 24 hour span here in St. Louis… it made the news for flooding.
Have you seen this used with travertine tile in an outdoor pool deck in Florida?
Travertine fits together so tight, I think stone dust would be too big. I’ve always seen travertine fit snug with no joint, no joint material.or, with some sort of product that I don’t use.
This article is awesome and thank you very much for your expertise!
I have a flagstone porch with flagstone stairs.
The only problem with dust is the stairs on the outside (front) edge of the stairs. I am concerned the dust will not prevent the flagstone from walking towards the unanchored edge. Maybe poly sand for the edge stones and dust for the rest? What do you suggest for front stair edges to prevent the stone from being tippy? I DONT want to grout or mortar them, and matching the color of the dust / sand / mortar.
Any suggestions?
Hello, and thanks for taking the time to answer our questions.
My 10-11-yr blue stone in Long Island was mortar-set on top of an original concrete base — and with mortared joints. Flagstones tend to be larger (2’x3′ or 3’x3′), mixed with some smaller units (1’x1′ or 1’x3′). Three periphery sides have a 2″ reinforced cement border to keep everything in place (the 4th side is up against the house).
Joints are aging well. Some are 10 years with no problems. Others seem to crack every 4-5 years (near roof leader downspouts and a few other areas that take longer to dry out due to adjoining vegetation)
While grinding out the joints, a few stones separated from their base. They all set back nicely without any wobble (even after walking on them).
Do I just mortar the joints nice & tight and call it a day…. or do I need to first bind the bottom of the blue stone to the old mortar base somehow —- before I mortar the joints?
Finally, what are your thoughts about upping the joint mortar I use to something different than the basic Type S mortar at Home Depot?
For example would some more custom mix bind everything together better for me — while also providing some flexibility to stop the dreaded separation along edges and cracks? Am looking for the classic very light grey or whitewash joint color.
For example, something like this: https://www.glengery.com/mortar or maybe something from Sika?
Many Thanks!
Yes, whenever you grind out mortar joints between flagstone, I pretty much expect a stone or two to pop up lose. Since the stones fit back nicely into place, only the seal between the mortar and the stone has broken–I recommend using pl loctite premium: https://amzn.to/3z9FWTi They sell it at depot and lowes, in the caulk isle.
As far as separation along the cracks goes–this is a matter of technique, not of product. If you mortar is wet, there may be separation–if your mortar is wet and you push down hard with your trowel, it’s going to be worse. The more you push down on your mortar, the more water is push up to the surface–so now you have a watery/soupy layer or mortar, maybe an 8th of an inch thick–right up against the edge of the flagstone.
A soupy mortar is a weak mortar. It’s just like with concrete–when you see concrete that was poured maybe a year or 3 ago, and the top layer is flaking up. Their concrete was too wet and/or they overworked it, troweled it too much and brought too much water to the surface. Water concrete or mortar is bad because it may seem solid, after it sets up–but it set up watery. All that space that was filled with water is now air, so it’s a weak concrete. or mortar, in your case.
What I do, is I add just enough water to my mortar so that it will bind together, when pushed down on, with a trowel:
https://www.devineescapes.com/flagstone-walkway-re-pointing-repair-paoli/
Called a powdery-dry mix.
Other times I go with a crumbly-dry mix. This mix is damp enough that it clumps together without needing to be smooshed together with the trowel–but just barely:
https://www.devineescapes.com/replacing-the-cement-between-flagstones/
This second method doesn’t clean up quite as easily as the powdery-dry method. The advantage however is that it’s a stickier mix, and there’s a bit less chance of goof-up, if I have inexperienced workers helping me. With the powdery dry mix you really need to push down hard with the trowel (it’s so dry a mix that you will not cause a problem by pushing down, firmly, there’s pretty much no water to push to the surface)–so it’s easier to goof up that method.
So I prefer the powdery-dry method–if I’m working solo, usually. Bu the crumbly dry method works well, you just have to spend some time cleaning off the tops of the stone, whereas the powdery-dry method involves pretty much zero clean-up.
The other thing to watch for, as far as separation between your mortar joint and the edge of your flagstone–is getting everything clean. After grinding out the joints you water to broom up all the debris, then blow off all the dust, then hose off all the dust..and get those joints nice and clean.
Other times, I go with a crum
Devin, Thanks for your response.
It got cut off mid-sentence and I’d hate to miss anything important.
Also, do you have any mortar that you prefer over another? Does lime really extend the life of the mortar joint?
Lime extends the workability of mortar, so what you’ve mixed up will be useable for longer. It also creates a creamier, stickier mix that a lot of guys prefer. Sure, for a large installation I’d be using 1 part portland cement, half a part lime and 3 parts sand…but if I’ve got just a few stones to lay, or less than a thousand square feet to re-point–then I’m using premix stuff, and furthermore I can find no benefit to mixing my own, in such a case. Quickrete “mason mix” type s. Green bag. It works well.
https://images.homedepot-static.com/productImages/8f8e41ef-21f0-4fba-beda-fcb652335ff0/svn/quikrete-masonry-mortar-mix-a003a-64_1000.jpg
It already has plasticizers added into the mix, to increase workbility and stickiness, no need to add lime.
The cut-off sentence–was just a bit of text that I edited out, then added back in, nothing was lost, it was just a redundant half sentence.
My paver patio, installed by a previous owner, had no base at all. Just sitting on a little sand and a lot of clay. Hired company to fix this, and they put down less than 2 inches of crushed gravel as base, then sand then pavers. Finished with polymeric sand. Resulted in ugly haze. Now they want to put a sealer over that! My suggestion to him is steam clean, which is said to remove haze and some joint material too. Then I would like to avoid more polymeric sand, and use what you have described instead. Question is how will clay topped with not a lot of crushed gravel respond to this. Patio is sloped but not very much. What do you think?
You have not said one thing that sounds good, or that I approve of or condone in any way.
Bulldozer or dynamite will be most expedient, but you can probably do the deed with a pick axe/pick maddock, and a wheelbarrow and shovel. Do a proper foundation, use real stone not pavers, pitch it 1/4″ per foot, forget about poly sand and forget about sealing.
But okay, if you’re going to live with what you have then yea, stone dust is a much better option than poly sand. If the foundation is nominal, then there may be shifting. That’s not a problem for stone dust, whereas poly sand, in a shifty situation, will crack up and be a problem. With stone dust the most you have to do is top of the joints every once in awhile.
Hi….wondering if I can use polymeric stone dust over dirt? I already have my flagstone in place however the dirt eventually washes away with all the Calif rains we’ve had and constantly needs more dirt placed between the flagstone to keep them in place. I really don’t want to have to pull up my flagstone…I’m 74 and that seems like a whole lot more work then I would like…thanks, Catt
By dirt, you must mean soil. of some sort. What, are you putting topsoil up in there? Stone dust AKA pathway fines, or decomposed granite is what you want to use. As described, in the above article. Never should anyone ever use anything similar to polymeric sand–ever. Just don’t do it, for the love of all that is good man.
Hi Devin, been searching and searching and you seem to be the most knowledgeable on this subject.
I used screenings for my joints in a dimensional bluestone patio. Every time it rains it washes out some of the dust and chips, and leaves an ugly film on top of the stone which needs to be repeatedly washed off.
Advice?? I hoped the siloxane sealer I used on the patio would bind the joint material but not really. Is there anything I can use to keep things in place?
Thanks!
Dave
Don’t leave the joints filled all the way to the tops of the stones. Screenings / stone dust joints should be filled, and have their excess brushed away, and be well washed and hosed heavily into place, leaving the final joint perhaps a quarter inch recessed from the flagstone tops.