Devin Devine, contractor based out of Blakeslee Pennsylvania, projects competed across the USA
contact devin@devineescapes.com
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Ask Devin: leveling dry laid flagstones in stone dust/fixing loose or wobbly stones
an in-depth guide
Hello and welcome to another addition of Ask Devin.
Hi Devin,
Do you have a blog post that addresses how to repair dry-laid flagstone patio? Curious about what the DIY steps are for dry-laid flagstone when there are loose stones. Thanks!
Noelle
“Loose stones” in a dry laid patio–I take it to mean that you have wobbly stones, that pop up when stepped upon.
1. Lift the stone out of its place. I used to recommend prying up the stone using a brick hammer, but now, or possibly with a vacuum powered tool, which I’ve reviewed here. If you are using a brick hammer, be sure to turn the hammer side-ways to left the stone up just an inch or two.
2. Level out the stone dust where it was, as needed. A square trowel may be used. (Yeah, I have mag floats and steel floats and whatever, but stone dust spreads well by hand and that’s what I usually do. The stone may not be perfectly flat on the bottom…so it may need more stone dust on one side, less on another. Adjust accordingly and then place the stone back where it goes. Hot Tip A 2″ level may be used well as a rough visual guide==if your level is 2.25″ thich
3. Check its level, in relation to the stones next to it. Might need to lift the stone again, and re-adjust the leveling material (stone dust). If the stone happens to be only slightly too high, like an 1/8″ of an inch or so, then you can persuade the stone to settle down a bit, using a dead blow type mallet. I prefer using one with replaceable heads, similar to this one here.
4. Check for wobble: put your weight on the stone, leaning on to it, corner to corner (I’m on the ground, wearing knee pads when I do this, leaning my weight unto the stone with my hands). If you push down on a corner and that corner sinks, while the opposite corner rise up–then you know the corner that sank need more stone dust. At this point, you can probably just lift one side of the stone up, rather than removing the entire thing all the way out, and then toss a hand full of stone dust under the stone, at the corner that needs it. Often I’ll intentionally add just a bit more than I think it needs…then mallet it down into place.
This video illustrated how to correct a wobble:
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stone walkway in progress, in Rehoboth Beach Delaware. In this photo, the entire walkway has been puzzled together, and is in process of being leveled. The stone to the left has just been lifted out of place and laid down, while the bedding material is being added, to bring it up to proper height. Finishing trowel, mallet and level, all within reach.
As you can see, steps 3 and 4 may involve a bit of back and forth, Just take your time, and don’t over do it with the mallet. Well, if the stone is a good 3″ thick, then yea, you can probably mallet away and pound it down to proper level. If the stone is only an inch and a half or less, then tap it down more gently, otherwise you may break the stone.
5. Repeat, correcting wobble for every stone on your patio of walkway. As a pro, I never have a patio truly 100% wobble-free at this point. I check each stone, on my knees, and get them each seeming wobble-free, but then when I get up and walk around, I’ll notice maybe one or two stones will have a (minor) wobble underfoot. So maybe the patio is about 85% wobble free at this point. The next step will help with that.
6. Refill and top off all joints, with new stone dust. Sweep off the excess, then hose down. Top off joints that settled during hosing…sweep off again. When I’m done, joints are just shy of being flush with the top of the stones. You don’t want to leave joints over-filled, as the material will be all over the stone surface, and will be a bit of a mess. Now, that the joints are filled, the flagstones are looking more like 93% wobble-free. Minor wobbles–no stone should actually pop loose, when stepped upon.
Minor wobbles that still remain at this point are only noticeable if you’re looking for them. Quit looking for them.
Over the next 6 months or so, the stones joints will settle in, harden up a bit and when I re-visit the job site 6 months or a year later, they’re just about always approximately 100% wobble free.
Note: for new installations, I lay out the entire puzzle first, figuring out how each stone is to fit together, and cutting as needed. After the stones are all fit together, then I go about leveling them off, one stone at a time, with stone dust.
Related content: how to cut flagstone using a hammer
first the puzzling, then the leveling
Tools needed:
- UPDATE okay, thanks to the new grabo tool, we have a new way to lift flagstones out of place. Makes the work a LOT easier! New tool, have never seen one at lowes or depot. Buy one here.
- Level (wooden if you’re getting into the trade, or a regular carpenters spirit level, if this is a one-time task for you)
- Knee pads
- Dead blow type mallet. For years I used one with replaceable hard and soft faces, like this one here. For the past couple of years I’ve been using a rawhide type mallet…..but can’t find a link to one that I feel confident recommending. Really, the 2 work interchangeably and I’ll still use the replaceable hard and soft faced mallet, if the rawhide is out of reach.
- Pry bar or rock pick (AKA brick hammer) type hammer for prying up loose stones. You can buy one here. Home depot/lowes usuaully has rock picks too, but they always have steel handles, never wood. If using a rock pick…..always buy wooden handled hammers. Steel reverberates too much. Plastic isn’t good. Go with wood. BUT you can’t use a wooden handled hammer as a pry tool, the handle will break. Okay….thing is, you don’t actually pry with it…..you place the chisel end of the hammer into the crack between the two flagstones and then turn the hammer to the side–rather than prying back on it. All the force is upon the steel head then, not the handle. Most of my readers are home owners….just use a claw hammer or a wonderman bar. (UPDATE, yeah, we usually use the grabo for this nowadays)
- 5 gallon buckets to carry your stone dust
- square trowel/finishing trowel (for smoothing out stone dust. bare hand works too, especially as you get better at it)
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DIY Flagstone and Hardscape help
My rates for DIY consultations are as follows:
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shorter questions may be answered for free in the comment section below…that’s how the present article was started, from a comment on another post.
Flagstone walkway in Wayne Pennsylvania
Related articles, DIY and hardscape how-to:
- how to build a dry stone wall
- how-to cut flagstone using a hammer
- building a stone patio overview
- what to use for under flagstones, concrete, sand, gravel, or what?
- what to put between your flagstones, sand, mortar, polymeric sand…..or stone dust?
- should you seal your stone patio?
- replacing the cement between flagstones, re-pointing
Will concrete fines work in place of stone dust?
I take it you mean recycled crushed concrete. In short: yes, concrete fines should work.
I’ve used recycled concrete as my gravel base many times, with no problems. In every one if those instances, I used crushed stone for my fines, to use as a leveling agent and as joint material. But so long as your crushed concrete is graded to consist of quarter inch ( or similar size ) and smaller bits all the way down to flour sized particles, then it will work. I can say this with confidence from having handled the larger sized crushed concrete road base type gravel–it performs the same as similar sized 3/4″ minus crushed stone, so 1/4″ minus crushed concrete will likewise perform similar to equally graded crushed stone.
The important thing is the size: you want quarter inch (or 3/8″) sized chips, and flour. This will serve well as leveling agent and joint material.
IMPORTANT NOTE: recycled concrete may possibly contain toxins–if the concrete was admixtured with fly ash, for example. Or an acrylic additive. I’m not saying this is a no-go, but do some research and decide: will children be playing in the stuff? Are edible veggies going to be grown nearby? What percentage of concrete contains such toxins and how bad are they? As such….I consider it ok to use recycled concrete as a buried foundation, well contained…. But I have some concern about it being used as the joint material.
I’m about to start an irregular bluestone patio and I am looking at purchasing some thermaled irregular so it is all pretty uniform thickness. Should I put down a 1″ layer of screenings on top of the compacted 2A base or is it OK to just lay the stones on top of the 2A and only add the screenings under the flagstones that need to be leveled out? The gaps would be filled with the screenings – will this be enough to hold them in place or do they need a bed of screenings to sit in? Thanks!
If you got your 2a base gravel perfectly level…this could work. Experience tells me you’ll end up having to raise a few stones, with a bit of stone dust, and you’ll have to sink a few, by persuading them down with a deadblow mallet. This fine-tuning of the leveling will be harder to accomplish, on a 2a base. The base, once wetted down and compacted is truly rock hard, and will make it hard to sink a flagstone.
For my money, here’s what I’m doing: I’m not even looking at thermal irregular bluestone. In my opinion (just my opinion) it comes out looking too perfect–looks like a manufactured product. Looks like a concrete paver, like faux stone.
Unskilled contractors love the stuff–because it takes less time to level. And hey, you can just leave the gaps wide and fill them with polymeric sand. Sure, the polysand will crack up and be gone in 2 years. Who cares! And since the flagstones are uniform thickness…hey, you don’t need the skill to fit the stones properly nor the skill to level them off. Just hire unskilled labor and pay them peanuts, sell the customer a job that’ll look sorta good, for a couple years.
The thing these less skilled, or less caring contractors don’t know? Leveling off the flagstones is a small part of the labor. The real challenge is fitting the stones well. I have an article for that. There’s a video, in that article too.
But if I really had to lay a patio using this thermal stone business….
I’d do it like the paver guys do. I’d treat them flagstones like as if they were pavers:
1. Set out 3/4″ (or 1″) steel pipes about 3′ apart from each other.
2. Get my pipes pitched the way I want the patio to be pitched.
3. Use these pipes as screed rails with which to level out stone dust, using a piece of 2 x 4 or a 4′ level to drag the stone dust out.
This extra step (of using the stone dust/screenings) may seem like extra work, but it’ll make the leveling out process a lot easier, compared to setting flagstones down directly on compacted 2a modified gravel.
Thank you for the quick response and info – much appreciated!
We have a flagstone patio around our pool. It gets scalding hot in the sun. Any products available to keep the stones from retaining so much heat? We are in the Lehigh Valley. Thank you!
I have 3 suggestions:
1. Replace the joints with a lighter color material. An off-white stone screenings exists and is findable in our area….you would have to call around though, and ask for “white screenings”.
2. Create some shade. A log arbor, or a trellis. It can be something beautiful, made from natural materials, or milled lumber. I know a couple of guys (yes, I make them out of logs sometimes). Or a canopy or steel gazebo can be purchased. The economy option would be a sun sail, basically a cloth tarp designed to keep your patio shaded. This is the most correct answer to your question possible: find a way to create some shade.
3. Replace some of the patio stones with white mountain flagstone. Being white in color, this type of flagstone does not get hot in the sun. It does tend to patina into a dull gray, but still much lighter in color than Pennsylvania bluestone, or even west mountain flagstone. White mountain is actually made from west mountain stone, at the quarry they separate the whiter parts of the stone from the brown and yellow tones, and cut out white pieces. Or you can get west mountain thermal flagstone, which is white and tan/orange swirly pieces, like what I used for this bench top:
https://www.devineescapes.com/wp-content/uploads/2021/01/Image8-980×551.jpg
For the most part though, the correct answer is still: find a way to create some shade.
My flagstone patio was laid professionally on a level concrete slab. Dirt has accumulated under some stones, where the concrete has come out over the years making them uneven in some places. Can I simply lift the stone and remove the dirt and do I need to use anything to make it adhere to the concrete slab?
There’s too much here that I don’t know. The flagstones were ;aid on a concrete slab–then why/how is there soil underneath them? Did they dry lay n top of an existing pad (leveling stones in stone dust or sand) or did they wet lay on an existing pad (in mortar) in wet lay on a new pad that they poured? How many years ago was this installed? How thick are the flagstones?
What condition is the slab in, is it all cracked up or fairly solid?
Devin, it has been six months since I consulted you and want to update you on my black lustre flagstone walkway. After taking a considerable pause I decided my best course of action was to let the stones and base material settle out over the summer and fall before resetting everything. I view my walkway more as art than I do a necessary foot path. Yes, I still have large gaps and yes I still have some small stones.
There were and are two issues. The first being it is my project that I planned and executed. The second and perhaps more important issue is selecting the stones. The last delivery of stone was much thicker than I can.desired, rendering it unuseable. That was back in January.
Should I suddenly strike a find of stone 1.25″ to 1.75″ I will replace what I can.
I appreciate the advice you gave me and I will check back with you next winter.
Have a great summer and year!
They sent you stone that was too thick? Sorry to hear that!
Usually, I visit my suppliers in person, and select which pallets of stone I want–or hand select individual stones. These days however, flagstone is in short supply and high demand–which sort of sucks. Unless you are a quarry owner. Every bluestone quarry seems to be backed up right now, 2 month wait on any flagstone. As such, I’m not even taking on any flagstone jobs, until things simmer back down, or circumstances improve. Taking on walling jobs, building birdbaths, doing consult work–but my old bread and butter–flagstone work? Well, I have a couple of flagstone repair gigs booked, but not doing any new installs.
Send a photo of the stone in question (or post it here) . Is it bluestone? Bluestone is a layered and can often be split along its end-grain. Like opening a book.
Hey Devin. How are you?
I live in the Ottawa valley in Canada and we
have a beautiful stone home we bought 4 years ago. With it came a big
multi level limestone and flagstone patio with big limestone steps
(like a terrace). It’s very creative and very ummm messy. It’s
likely about 12 years old and there are signs that the previous
owners have filled big huge 2 or 3 inch gaps/cracks with cement. I imagine this is from the freeze/thaw we get here every winter. I can see these cracks used to have soil/limestone dust but has washed away with rain. I am a DIY kinda person, so I’m looking for some advice, however I don’t see any jobs on your site that accurately describe my situation. Any suggestions?
\Im very much considering the 1hr advice call with you, just thought I’d ask here on the site.
The patio needs to be re-laid. Stones were never really properly fit, with large and irregular joints in places, and too many small stones. Maybe 20% of the existing flagstones should be rejected as too small. Bring in some larger pieces and re-lay with better fitting.
Large joints that are filled with soil are going to be very weedy….regularize your gaps and fill the joints with stone dust. You’ll get significantly less weeds and when weeds do happen, you can treat them with the torch, as you have been, or with boiling water.
Even if there was a quick fix for your joints….the stones still need to be re-leveled. There is some sort of border between the lower patio and the upper patio…where there first is a 6″ step, but then there’s there’s border stones that seem to be an inch and a half or two inches higher than the lower patio. Something needs to be re-leveled then. Other border stones, with large open gaps, should be set closer together.
Shoot me an email if you’d like individual guidance on this situation.
Thanks Devin, very helpful!
Hey devin… First man thanks for having this forum and posts. I just received 1600 sq ft or what must be close to 18 tonnes of local flagstone from Nanaimo in British Columbia. Crush base is in and compact but there is a bit of sand already down… I was going to lay more sand but after reading your post will be ordering stone dust instead, what you said about the ants is spot on. I had this at my last place in Ontario… Big question is.. Im doing this as a pool surround and deck area… The pool is ICF with concrete and has an automated cover. The rail is made of steel.. Looking for ideas suggestion on how to secure that first row of flagstone as pool coping on top of the rail… Flag is 2 – 2 1/2″… cheers grant…wish me luck, I start hand balling the flag tomorrow from drop point to pool area in 30 plus c heat…
Hello. So, you’re asking me “how to secure that first row of flagstone as pool coping on top of the rail”.
Wait, the rail will be on top of the flagstone–not the other way around.
Are you asking me how to secure dry laid flagstone as pool coping and then secure a railing to the flagstone? In such a case, I would mortar the coping. It’s sitting on top of a concrete wall, it should be mortared down. You can do a irregular coping and surround that with dry laid flagstone.
So here, they poured the concrete for the pool….and then laid out their flagstone coping–then went back and poured small concrete extensions attached the pool wall…..and then went back and set the irregular copings on top of the pool wall.
Okay, in case that isn’t very clear: what we did is we dry laid out the coping stones. The pool wall was maybe 12″ thick or something like that, with irregular flagstones overhanging the pool wall by a few inches here, a foot or so there. We then spray painted a line around these stones, lifted the stones up, and set concrete there, then came back and set the stones on top of that.
Thanks for the response Devin.
I’m looking for ideas how to secure the flagstone on top of the rail for the autocover.
Pool concrete is already in. Rail is already attached to the concrete pool wall. Pool has already been backfilled.
G
I can’t picture it. Post a photo…. If it’s an easy answer, like “use glue” then I can do that here. If I need to engineer something new, then I can do that with a one hour consultation.
devin@devineescapes.com
Hi Devin,
I perfectly agree with using limestone screenings to fill the
gaps between flagstone pavers. Did it in the parks in Chicago.
Pictured is my flagstone patio in Prescott, Arizona, gaps dug
out and ready to fill.
NOW, where do I buy that screening in this part of the country?
Thanks.
Whin Oppice
Prescott, AZ
In my experience, you should be able to find stone screenings pretty much anywhere…only problem is, every state seems to have a different name for it, often multiple names in one state. In California I purchased “pathway fines” (that’s as close to Arizona as I’ve gotten, for patio construction. So far. Elsewhere I’ve seen it sold as quarry dust, stone dust, 1/4″ minus, 1/8″ minus and more.
What I do, whenever I’m working in a new state, is I call or visit the local masonry supply/hardscape supply yards–they all carry it. Or the local gravel quarry. If I’m in person, I’ll just walk around until I find it–or if I’m on the phone, I’ll just describe the material I’m looking for, “crushed stone in the smallest size you carry. I’m looking for eight inch, or maybe quarter inch sized chips of stone, with fines.” If they don’t know what fines are then they are probably a high school kid or something….but I’ll try replacing “fines” with “stone dust”.
Decomposed granite is the same thing–just made from granite, and usually more expensive than sandstone, argilite or limestone screenings.
BTW You’ve done a good job of fitting those stones together without making any cuts (that I can see). But to make my system, as described in this blog post and many others, to make my system work at its best and to minimize future maintenance–you’ll want to close up some of the larger and more irregular gaps.
This article offers some advice on stone cutting–the article has information and a video which will help you, if you choose to follow my advice and try to fit these stones together better. If you choose to do what I am suggesting, you will need a brick hammer, and patience–and even if you have plenty of patience, an angle grinder with diamond blade may be a big help.
Then again, you’ve fit these stones better than most home owner installations–and better than many so-called professional installations so….I understand if you opt to forgo the extra cutting, but I urge you–Spend an extra day of work now and it will save you that much time in maintenance, over the years
No luck today for limestone screening with fines/dust. Decomposed granite is mostly used in these parts (Prescott, AZ) but not very eye appealing and I don’t believe it ever compacts itself as does limestone. Please write if anybody knows where to get the limestone. Thank you. – Whin
DG absolutely does compact….any crushed stone, with fines, will compact. I rarely use limestone….hardly anyone does…..but argilte, sandstone, slate and granite are all being crushed, every day, all across the USA, into good quarter inch minus (aka fines) type material.
OKAY, so I just googled “prescott az gravel crushed stone”
And the very first result is a place called MDI rock….
I clicked on their website….
Then I clicked “rock” under the heading “products”…
And their it is, bottom left corner:
“1/4″ minus iron springs gold”.
https://www.mdirock.com/products/rock/14-minus-iron-springs-gold
THIS is what you seek. If you don’t like the color….well it took me 30 seconds to find one. Good chance you may be able to find another. If not local, then a bit of a drive. Pretty much any gravel quarry….
Thanks Devin for encouraging me to go ahead with the decomposed granite in my part of Arizona.
“DG absolutely does compact….any crushed stone, with fines, will compact .”
Got the DG 1/4″ minus at MDI Rock in Prescott. One bucket (painter’s pail) cost $3. Got started today. See photo at your email.
Whin
Good. Be sure to hose the DG down really well and sweep away any excess. When finished, the DG should be an eighth of an inch or more shy of the top of the flagstone and it should not get all over the surface of the stone, but should stay in the joint.
The smaller stones you’ve used concern me a bit–the fact that all the small stones (that I can see) are near the border of the patio, where people are less likely to step, is better than if the small stone were out in the middle. Small stones will pop up underfooot, requiring future maintenance…
Making them fit better.
Cutting them, for better fit.
For best long-term performance—replace these small six inch or so pieces with larger.
I am making an assumption that you level the stones one by one. I’ve noticed others lay the leveling substance (sand or crushed stone) over the entire project and then start fitting the stone. Why do you do it stone by stone?
Paul Tomme–you just made the one thousandth comment on my blog! Guess what you win–nothing!
But anyway, I level the stones one at a time because the stones are of varying thickness. You can lay out all of the bedding material in one go, at one inch thick, by screeding the material out using a level or a 2×4 to drag the bedding material across 1″ pipes…but only if you are using faux stone which is of uniform thickness–or, if you’re using sawn-thermal stone, which is likewise of uniform thickness. Personally, I won’t mess within any faux stone. The world is made of real stone, so why bother?
So sawn-thermal is going to be be easier to install than natural cleft….but with the uniform surface texture of sawn-thermal, a patio can end up looking a bit manufactured. Around 99 out of a hundred times I’ll prefer natural cleft to sawn-thermal. Sawn thermal material will cost more too. Sure, it saves you time leveling…but then leveling is not the big time consumer, puzzling the stones together is.
And don’t use sand.
I’ll try for 1,001. Speaking of “not sand”, I can easily and cheaply get 86 Granite and “fines”, I can truck in “screenings” from one out-of-town company, but it is expensive. Do I substitute fines or 86 for screenings? Or do I throw a bucketful of fines into a wheelbarrow of 86 or vice versa? One landscape supply company suggests (probably because they don’t carry screenings) using fines instead of sand.
My preferred leveling agent and joint filler is quarter inch minus–that’s quarter inch chips of stone, with fines.
Eighth inch minus is just as good. When I’ve seen material sold as “fines” or “pathway fines” it was usually eighth inch minus material
If however the fines contain nothing but fine flour-like material…. Then I might mix in some quarter inch material. Where are you located, and what is 86 granite?
We are in the Atlanta Area.
#89 Granite Stone (Sorry) is granite crushed and screened into pieces that vary in size from 1/4″ to 3/8″. This is also the smallest of the granite stones. Commonly used in concrete, asphalt, retaining walls, driveways, drainage applications, and walking trails.
What I have seen so far is very clean #89, not much dust.
It took a lot of searching, but I found Alabama Path Stone: 1/8″ to 1/4″ with 50% fines. It is deep red, which will work well with the brown Tennessee flagstone.
Excellent, glad you found it.
Again, great site.
After site prep for the entire 480 sq. ft. project (2 paths and a patio), we finally got the patio (11×14′) finished. For those of us with no experience, it took 5 days to shape the flagstone and layout the pattern and another 2+ days to level it all out. We used a 50/50 mix of granite fines and crushed #89 granite (+/- 3/8 inch) for the leveler and placed the stone about 1 inch apart. For those of us fortunate enough to live in the SE, we were able to use Tn. Variegated Brown (Crab Orchard) flagstone. I did handpick mostly peach swirl stone.
I’d love to send a picture, but I am not sure how.
You can upload a photo to a site like https://imgur.com and post the link here–or just email me the photo and I’ll edit your last comment to include the photo. I’d love to see your finished patio. Have never had the pleasure of working with Tennessee flagstone.
I sent you an email with the photo attached. The Crab Orchard is beautiful but much more delicate than something like slate. You can really tell it is sandstone; it splits off layer by layer and unfortunately the prettier the individual stone, the more delicate. [We absolutely made sure that there was no wiggle in any stone.] When we complete the pathways I’ll send another picture: you will see the complete range of colors available. Because I ordered 3 pallets, I had the option of picking a color scheme for the patio. “Peach for the Peach state.”
WOW, you did an awesome job! I can’t even tell you how often I see “professional” installations by masonry contractors–that do not look this good. This, is a beautiful thing! Nice consistent joints and well fit stones.
The Tennessee flagstone is nice. Gonna have to build with this stuff, some time. Thank you for sharing this!
Great conversation here! Question for you:
I am looking at purchasing 1″ thick bluestone here in Ohio. They are 24×30 and I would like to ‘dry lay’ these on 1″ of screenings above 4″ of heavily compacted 2A. This is in place of pouring a concrete pad and mortaring the 1″ thick stone. I’m also planning to use a concrete style edging (Permaedge) around the perimeter, but am curious to if that’s smart with freeze/thaw here in the midwest, and a dry laid sub base.
The space will have a nice consistent 2% slope. My only other thought was using a sandy mortar mix to (4 parts sand to 1 part Portland) and using that in place of the 1″ screenings – but I’m thinking with a solid 4″ of 2A on a compacted sub soil, we should be good with minimal risk of the stone cracking.
Any thoughts? Cheers
A few things. First of all, 1.5″ thick flagstone. 1″ is fine for wet-laid, for dry-laid, go with thicker stone. And for the foundation–again, I go thicker. Here in Pennsylvania, we used to go with a 4″ thick compacted 2a base. In 2007 I began going with a 6″ base….and over the years, I’ve seen more and more contractors do the same, to where that has become the industry normal. In my opinion, a 4″ gravel foundation, in a northern climate–has a chance of heaving and/or settling. I don’t know what that percent chance of failure might be, I just know that my way of doing things has resulted in zero warranty calls. Back when I was a young man and employed by another company, we did do 4″ thick foundations–and that company had a warranty call or three, each year.
Are for portland cement–that’s a big nope from me. It will crack. To be fair, I’ve seen dozens of patios like this, dry laid, with portland cement in the joint–and one of them (only one) was not too terribly cracked up.
As for concrete edging–I’m not a big fan. My recommendation is to only use larger stones along the perimeter, stones large enough that they will not shift underfoot. No edging needed.
Hello -Your site has been so helpful. I’m laying a tumbled bluestone patio. The stones have a cut but tumbled edge and are 2” thick so the gaps between stones will be pretty tight. Here In Wisconsin we have two main leveling agents to choose from: Torpedo Sand (also called washed concrete sand) and lime sand that I think is what you’ve described as stone dust but here we have it from limestone. Both are 3/16 or less. Would you recommend one over the other for the leveling base and filling the gaps between stones? I already have a 6” base of 3/4 crushed limestone traffic bond gravel. Thank you!
Ants love sand. I’ve seen too too many patios and walkways undermined to the point of be unusable by ants. As such, torpedo sand is out. Crushed limestone gives me some concern too as is can retain water for a bit longer than crushed granite/sandstone/argilite/what-have-you. I’ve call around–any quarry that produces gravel will also produce screenings/quarry dust/fines/quarter inch minus/thee sixteenths minus/decomposed granite, or whatever they call it in your area. Crushed limestone…..I’ve seen cause a problem, by retaining water, once or twice over the years…..so I’m not super concerned about it. I’ve even built a project or two myself, back in the day using the stuff, and didn’t hear back about problems. But if you’re going to have both crushed limestone for the foundation and for the leveling agent/joint filler, then I’m a bit concerned. If you told me you don’t get much rain or that the patio has a roof over it, then I wouldn’t worry.
I’d call around and find non-lime crushed stone fines. Either a quarry has it in bulk, a masonry supply place in bulk, or a landscape supply place might have it bagged (probably DG, if it’s bagged). Failing at that, I’d still prefer the lime sand over the concrete sand.
Having said all of that–it’s still not the most crucial decision here. Tumbled bluestone usually means there’s basically no gap between the stones–the stones can be set touching, and the joint is more just from the stones being beveled/having a rounded edge. So we’re not adding much lime between the stones and also, since the stones are uniform thickness, you won’t need tons of leveling material anywhere–you could even screen a 1/2″ thick layer of material out…
I was wondering about the thickness of each course under the slate/ blue stone walkway. i.e. 4″ compacted gravel sub-base, etc. We are taking bids for the large job and the town has requested a detail. we want to use poly-sand because the stone dust doesn’t work for this application. Thanks in advance
Polymeric sand comes with a host of problems. First of all–it’s a bad system to begin with. Your joint is a solid piece…comparably rigid. The bedding material and foundation however are loose–and may settle. That creates a void. In the least, there’s a void underneath the joint now, and it will cause the joint to fail faster than you expect.
How come stone dust won’t work in this application? I’ve used stone dust for nearly every single patio I’ve built, north, east, south, west, rainy, dry, you name it. Never had a warranty call, in 16 years–and I frequently get called to assess poly-sand failures. Anyway, read all about it.
In Pennsylvania/New York and similar climates, I go with a 6 inch (or more) foundation of compacted road base type gravel, 3/4″ minus or similar. Colder/wetter locations, we’ll go 8″ or more.
In California and Florida, the industry standard is to go 3″….. when I travel south, I still do a solid 4″ for my foundations.
Flagstones should be around 1.5″ to 2.5″ thick. Much thinner than 1.25″ and you start to get into problems of stones breaking and/or wobbling underfoot.
Stone dust is used as a leveling agent (NOT concrete sand) at a varying depth of 0″ to 1.5″.
I’ve been dropping in pavers for a while not a professional or anything but just figured out how to do it done some driveways and pathways this is the first flagstone pathway someone is wanted me to do. it’s on a bank… Very large flagstone about 52 in average by 36-in 3/4 thick so I decided to leave it virgin ground instead of Base Rock for the base because the ground is so tough very stiff so I cut it out and I decided because of my paver background to put sand in as leveling agent.. but before that, i etched in an anchor border of pavers on the low side of the bank and end of path so it’s all locked in about 60 ft down by about 52″ across
This is all in Northern California by the way but the weather is really drying up so I’m not too concerned very much about wet weather lately we’ve been in a serious drought but anyways besides that I decided ahead of time to use decomposed granite as a joint between the stones I have already started dumping in course sand to help me level the Stone but now I’m thinking (and I’m wondering if you would say this is legit) of mixing polymer sand decomposed granite with the sand that I put in there so I don’t waste the sand that I have and then using decomposed granite with a hardening agent as the joints in between flush with the surface of the flagstone do you think this is a good idea?
… Would you approve of that?
Thank you in advance
I approve of the decomposed granite. I’ve worked in Northern California. You should have access to pathway fines–a crushed stone product similar to decomposed granite–use it interchangeably with DG. Just use DG when you want to spend extra money or when you want a specific color. I do not love flagstone being set in sand, as ants love sand. Crushed stone, whether DG or pathway fines, is a superior leveling agent to sand. Polymeric sand has no business being used with flagstone…no stabilizing additive added to the DG. No binders.
Mind you, I’ve also seen stone flour only “pathway fines”, where it was just the dusty flour-like fines, no larger chips of stone. Ideally, you’d be using a quarter inch minus, or eighth inch minus crushed stone product as both your leveling agent and your binder.
Hi Devin! Wow. Firstly, you and your website/comment section are fantastic. What a great resource. Thank you so much! My husband and I are embarking on a small DIY flagstone install, approx. 200 s.f. We are in Berks County, PA and are likely going to use West Mountain 1.5-3”. Poly-sand was recommended and we had some initial reservations about all of the concerns which you have thoroughly outlined. Our Google search about the poly-sand brought us here and we are 100% that screenings are the way to go. However, I’m concerned about the color. The West Mountain flagstone is predominately brown tones, some stones are quite light. It seems like the screenings are dark gray, almost black even. How does this contrast look? Do you have any photos of projects that you’ve done with a similar combination? Are you familiar with a supplier anywhere near Berks County that sells brown-toned screenings? Thanks!!
This walkway here was built using west mountain flagstone and screenings:
https://www.devineescapes.com/wp-content/uploads/2014/07/flagstone-walkway2-1080×806.jpg
Alternatively, I do know that there are landscape and/or masonry suppliers in Berks county that carry red screenings–I’ve purchased it before, outside of Quakertown somewhere. The dark gray/black screenings look good, but the red would be a good look, too.
Hi Devin! Your work is absolutely beautiful!! We are laying extra large Arizona flagstone on our front patio and wondering if there is anything to use sort of like grout but not grout that can have a little bigger space between and that is waterproof? I want to do like a sandy fine rocky grout like substance that will hold and what do I seal the stones with? Thank you for your time!
What you should want, rather, is to fit your stones together a little bit better. The joint material to use is crushed stone, stone dust–any substance that tries to do what you’re asking for– fails.
Read my article: Why polymeric sand is 100 percent no good at all, ever.
Never seal flagstone.
A joint that “will hold” creates problems, partly because it stays in place–while the foundation beneath it settles. Leaving voids. Creating problems.
A flagstone that has been sealed….is just a natural stone that someone couldn’t let be, they just were convinced that stones need an acrylic coating on them. But stones do not need a layer of plastic sprayed on to them, and doing so will only trap moisture and will more likely damage the stone, then protect it.
Love your blog. A quick question. I am putting down a front walkway with random sandstone rectangles – rough-cut on the sides. I have a 2-3″ compacted gravel base, and plan to use sand under the flagstone (whicH I already had delivered). The entire walkway is edged on all sides with corten steel. I like the idea of using Stone Dust as a filler. Is there an issue with using this as a filler with a sand base under the stone?
2″ to 3″ of gravel….I’m guessing you live in Cali, AZ or FL? Someplace warm, with rocky/sandy soil? I usually work in places that require 6″…and even in Cali, I’m using 4″. In places like Cali, 3″ is the standard.
Call your local gravel quarries, landscape cupply places and masonry supply places–someone has stone dust.
Wait–you found stone dust? Get that sand out of there–ants love the stuff and will undermine your walkway–I’ve seen it happen over and over then.
To answer your question…..yea, it’s fine to use stone dust as your joint, with sand being used as the leveling agent….no real problem there–other than the issue with the ants. And sand isn’t as sturdy and stable to begin with…for these two reasons your walkway will be much more likely to need significant re-leveling in a few years. Butr raking out the sand and replacing it with proper stone dust–you’re looking at spending an extra half hour of work and 50 dollars of product–get rid of that sand.
I’ve never used any edging, isn’t necessary.
Love your site, thanks for all the advice. Unfortunately I found it after I started putting in a flagstone patio, and now I’m trying to figure out how to fix my bad beginning….one of those cases where I knew just enough to be dangerous. Anyway, I put down my 4 inches of gravel base and realized I did not get the correct gravel with fines, but clean gravel. I tried adding finer material on top and repeatedly used a tamping plate, more fines, more tamping but still can’t get the surface to be hard set. I’m wondering if I should put the screened material on it anyway and trying tamping that down to get a better surface? I hope you have some ideas to help, thanks.
I’m assuming you got 1″ OR 3/4″ clean gravel. In a situation like this I would: rake out and remove a little of the clean gravel, maybe ten to 25 percent. Then, you need to add crushed stone. In Pennsylvania they sell it as “screenings”. In other places it’s sold as rock dust, quarry dust, etc. Add the stone fines and use a mattock to stir the fines and gravel in together. And/or use shovels and toss the gravel and stone dust together. Using water can help to get that stone dust settled down in there–but some gravel should be removed because in order to get good compaction, you need a sufficient percentage of stone dust and medium sized particles too. So ideally you would be buying a larger stone dust–1/4″ minus, rather than 1/8″ minus– and half inch minus would be even better, if available. I say this because good road base gravel is well graded–has 3/4″ pieces, has fines–and has all the in-between sizes. But if all you have is regular rock dust, which is usually 1/8″ minus–that should be fine. Unless there’s shifty soils, or tons of surface run off at your location –but in most sItuations, mixing the 3/4″ clean AND the 1/8″ minus will yield a sufficient base material.
Hey Devin, thanks for sharing all of your experience– this is great. Can you explain, or link to me a video you have of laying the screenings? From what I understood you explain, you fit all of the flagstone, and then come back and lift each piece out, and put the screenings under each one, put them back on top, get them level, and so forth. Am I understanding that correctly?
One more question: do you ever you a compactor for the screenings, or on top of the flagstone (with a protective pad)?
Thanks for the help!
Lift 2 stones out of position–then level one of them, Flip another stone out–then level one of them. This way, you don’t have to pry up stones that only have a small space between them. Use 5 gallon buckets, to deliver the screenings–you don’t want to work out of a wheel barrow.
Screenings are only used as a leveling agent–never tamped. No, do not tamp the top of the flagstone. Each stone, as I level them, gets a smack with the dead blow mallet. Often, if the stone is just a bit too high, when leveling–it gets many smacks with the mallet.
Devin,
This site has really helped me want to install a blue stone patio myself.
For a processed foundation do you recommend digging out and building up a full 1 foot past a finished edge, or does 6 inches work? Do you taper it up near the finished height?
Thanks for any help
I’m glad my site has been helpful to you, and appreciate your comments,as they help with my rankings.
I do my foundations 6″ or so beyond the finished edge. Often, it’s less than that, due to site conditions and we have a foundation that only goes to the actual edge of the patio or walkway. Or due to a last minute design change–the flagstone ends up, sometimes, going all the way to the edge of the foundation. I still do my foundations, usually, with 6″ extra on all sides–but over the years, there’s been many exceptions. These have never been a problem, and many years later the work looks good. I understand well the reasons why, structurally, it makes sense for foundations to be bigger than the structure they support. With dry laid flagstones however–the reason why I make my foundations 6″ bigger on each side–is mostly so that I have room to change the shape of whatever I’m building, slightly, as the work progresses.
Mr. Devine: I appreciate your site and all of the expertise you’ve shared with all of us – truly. Thank you.
One question I have is this: I live in Dallas TX and was going to put down a 16×12 natural stone patio (not flagstone but similar). I was going to dig down about 8-9″ and use stones cut to roughly 2″.
Do I use DG (all I can really get here) for BOTH the base layer and leveling layer? I’m at a loss as to what to use if anything different than DG.
Any input is most appreciated sir.
I did some searches looking for gravel suppliers in your area. This place has what they call flex base:
https://www.outdoorwarehousesupply.com/product/flex-base-regular/
It claims to be a larger aggregate (with fines) but they didn’t say exactly how big this larger aggregate is. It looks like it will work, and they claim it is used for roads–whatever they use under roads, locally, is generally good to use for flagstone or other stone paving.
They also have flex base fines:
https://www.outdoorwarehousesupply.com/product/flex-base-fines/
They say this is used for underneath patios and retaining walls–so this is the stuff that they are recommending be used. 3/8″ is a bit small….in my opinion, for foundational purposes. I’d go with the larger stuff–though we don’t know how large. I’ve used suppliers that had 3″ chunks mixed in with their road base gravel–it works great and I’d trust a foundation like that, over a foundation made with just fines.
The larger stuff–will be a bit harder to rake is the only thing, but like I said, I trust it more, long term. Mind you–the fines would work too, just will be more likely to have some settling, in a few years, might end up needing to re-level a few stones.
These flex fines will usually cost less than decomposed granite, too.
Thank you so much! I have checked out those products and they do seem perfect for the base but I’m left wondering about the final finish between stones. I was considering DG originally because it’d compact well in the spaces between the stones (planning on between 1-2″ spacing between stones). So, if I go with the larger stuff there, I won’t be able to use it for the top-most finish so would I need to do that final fill with something like G2 Gator Maxx polymeric sand?
The flex base for the foundation. Flex base fines for the leveling agent. If it were me–I’d use the flex base fines for the joint, too. 3/8″ is the largest size in the flex base fines, and that will fit in between flagstones.
But you could certainly use flex base fines as the leveling agent–and then still use DG for the joint–if you need smaller material, or if the color of the flex fines isn’t what you want.
Thank you again for all of your help and expertise – you’ve taken something a little daunting and made it very approachable. Thank you!
Devin…
I have read what you wrote on sealing stones and I understand why that is a bad idea. My question (and I did not see it elsewhere on your site) is this: is there anything that I can apply to the surface of the stone to help clean it from the initial cutting? I have raw/rough cut rocks that I’m having to trim down and to give a smooth top surface to them; I was just wondering if there is something I can apply to bring out its own natural color or luster? I’ve read that mineral oil may be an option but am not sure – I would appreciate any insight you may can give on this sir.
So you have tool marked stones, where you had to cut/grind/chisel stones flat enough to use as paving stones.
I know of no product that can correct this.
What I would do in such a case is use a torch. Oxygen acetylene cut torch, of the same sort that people cut steel with. I dampen the stone, then hit it with a blue flame.
Sounds like popcorn as little bits of stone flake off, via thermal spalling. The torch can be used to hide saw cuts, and will bring back a natural-like surface to the stone.
https://amzn.to/48Qamdu
Thank you sir…I’m good with the surface (I have it smooth already like I like it) but wanted to see if there was some way to bring out/back the color of the rock with something that is not a sealant. Most products out there advertise this but they are all sealants. So, the torch would be the best way forward you think?
You have it smoothed with an angle grinder or saw?
The torch will cause thermal spalling–the top 1/16th” of the stone will explode from the surface, exposing a more natural surface, which will be darker than a saw or grinder finish.
The other option would be to polish the stone. How many are there, how big of a space needs to be darkened though? Polishing takes longer. Also, polishing can make the surface potentially slippery–being outdoors, and exposed to rain.
https://amzn.to/3Fh4yMs
Use it with a variable speed angle grinder, dialing the speed way down to 2.
https://amzn.to/45BcClP
Start with 50 or 100 grit, work your way up to 400 and see if that’s dark enough.
400 and up–I usually switch it to speed setting 3, and use water.
But usually, I’d use the torch.
Sorry for the delayed response Devin. I used this saw to cut rocks from larger (on average 4″ high x16″ long x 5-8″ wide) stones: https://www.pearlabrasive.com/14-masonrybrick-saw/product/0/871638
The tops (cut side) are what I was hoping to bring the color out but also keep smooth (I wish there was a way to upload pics to give you a better idea). I looked at the spalling technique you suggested and that’s not the look necessarily I am going for so I do think maybe the polishing route might be more the way to go.
That said, I have a patio area of 16.5′ x 12.5′ and stones are ranging in surface area size from as little as 2-3″ wide & 3-5″ long to 5-6″ wide and 12-16″ long. The patio will be covered with a double-roof metal gazebo to keep most of the rain off.
Some rocks are more white, some more buff or oatmeal, and some more brown. I was attempting to effect more of a checkerboard pattern (9 large sections) utilizing the different colors as part of the design. After cutting though, the white and oatmeal rocks are just looking both white and the brown has a slight sparkle “quartz” type of effect. When I wet them, you can see the color difference of the white/oatmeal and the sparkle of the brown; when it dries it mostly goes away again.
Thus, I was wondering if there was a cost effective way (I’m ok with the labor part) to highlight that natural color difference but more on a permanent basis? I don’t need a glass finish on these since they are outside, but, a more permanent way to highlight those color elements would be ideal.
I know this is a lot and your time is valuable. I know this is not a full-blown consultation, but if I need to Zelle you a stipend for your extra help to buy you lunch, I would like to do that as a thank you for letting me bend your ear. I would just need to figure out your Zelle info.
Thank you,
Randy
That large of square footage seems like a lot to polish. If you were doing only half of the stones, it’s still a lot…but maybe doable. At one third–then you’re looking at 68 square feet. If you only need to darken a third of the stones, then polishing seems doable. Oiling the tops of the stone will darken them and bring out the color, making them look polished. Oiling will last less time though. How long it will last outside, will depend on your local conditions, and how well the stone absorbs the oil. Might last a year or 3–takes less time to do, and lasts less time, compared to polishing. Polishing also involved learning a skill–oiling however: just put some linseed oil on a rag, and coat the stone.
If you want to zelle me some money, that would be cool. Instead/or both, you could help me out by promoting my site. Presently, my site has been ranking less on google. If you have a social media, you could help me–by posting a link to my site, when you’re finished, and letting people know you found my articles helpful. Even if you have a small circle on social media, posting a link still sends a signal to google that is favorable.
And if you don’t mind–send me photos of the patio when finished, I’m interested to see! You can upload photos to imgur.com. Imgur will give you a link, and you can just share the link with me here.