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What to put between flagstone joints–polymeric sand or stone dust?
Polymeric sand is a product made from sand with an acrylic binder added. I first started seeing this stuff about fifteen years ago. It’s 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. Let’s examine these advantages one at a time:
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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.
Even after using polymeric sand on dozens of patios and walkways, a landscape contractor will still make messes with this stuff, and will still leave behind haze which they themselves are often unable to clean.
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.
3. Weed and ant proof. Polymeric sand is indeed pretty good on these fronts. But tiny cracks do form, and weeds will get in there, roots will grow, cracks will get worse.
What I use is stone dust 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.
Screenings 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 tiny
powder-like fine material mixed in as well. these fines, when dampened, actually do bind up with the larger chips, becoming semi-solid.
Screenings, 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 amongst my flagstones, as they do not seem to like screenings at all.
Polymeric sand cracks up, 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.
Now about weeds…what can I say? Life happens. Every once in awhile, you may have to pull out a weed. Acetic acid (vinegar) can also be sprayed 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. Especially if it is a patio that I built for you 🙂 seriously, that will not go over well at all. Send me an email, if you need weed care advice. I am always happy to help.
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?
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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.
In the north eastern region of the USA, stone dust, aka screenings, quarry dust, or grit, is very easy to find. Elsewhere I have seen it called Decomposed Granite. Here in Pennsylvania, quarries carry it, landscape supply places, nurseries, masonry supply houses–even some hardware stores carry it bagged. If you live elsewhere, then I’d suggest looking for screenings under one of the names that I’ve listed above. There’s plenty of local options that will work, wherever you are, each with it’s own advantages and disadvantages. Whatever you go with, I hope this article has been helpful.
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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 with almost 2 decades experience. One who just happens to enjoy writing, and likes to help people. But if you feel that you need help…then you’re going to need to pay me money via paypal, email me a photo or two, and we’re going to need to speak for 20 minutes to an hour.