I've seen some videos showing how to make "flagstones" out of concrete. The general process is to create a moulding on the ground (usually the grass is dug out so the dirt is exposed), using some sort of flexible strip of plastic or vinyl. Then, concrete is poured into this mold. In most of the examples I've seen, the stones look to be no more than 2 inches thick, but they can be 2-3 feet across.

I've been thinking of doing this to make a patio (though I'd probably put a layer of gravel below the concrete), but I'm concerned that these stones might be too thin and crack after not much use. Also, we get freezing weather in the winter, and I'm concerned that thin stones might crack in the cold weather.

How thick should these concrete "flagstones" be to ensure they don't crack?

( one example of the technique I'm referring to: https://www.youtube.com/watch?v=MNaVzbwuATI )

  • If you take a look at the prefab pavers at your local big-box store's landscape section, you'll see that most of them are only about 1.5 - 2" thick, so you're probably OK making yours that thick, too. I didn't watch the video, so I'm not certain - are you planning on casting each one in its final resting place, or are you going to cast in a mold in a corner of the yard then move them to the patio area and reset them?
    – FreeMan
    Apr 8, 2021 at 18:11
  • 1
    It would be much simpler and faster to buy artifical and. or natural flagstone. Apr 8, 2021 at 19:04
  • @FreeMan: The plan was to pour them in place. Apr 8, 2021 at 19:22
  • @blacksmith37: Some quick estimates I did suggested the concrete method would be cheaper than natural flagstone, but that also included the stone company preparing the site and placing them. I guess I could look around for a cheaper source that will just deliver and let me manage placement. With the concrete stones, I at least know the stones will fit well with each other ;) Apr 8, 2021 at 19:25

1 Answer 1


Typical pre-cast pavers are about 2" thick, so that's a reasonable experiential datapoint. I've got a few of those in the 16" square size that have been through 11 winters without cracking in a pretty serious winter area.

You can get fibers to mix into your concrete to help reenforce it - 2" is too thin for using steel reenforcement. Ensuring that your mix is not too wet when placed and then kept quite wet for a month after it's set will help ensure you get all the strength your concrete is capable of giving.

You could also pour a 4" steel-reenforced slab on gravel base, and just do patterning/dying on the top surface for the flagstone "effect" - products are sold for this exact purpose (or crews to do so can be hired, preferably after reviewing jobs they have completed.)

  • 1
    How you prevent frost heave for cold regions, any suggestions?
    – r13
    Apr 8, 2021 at 18:11
  • Drainage. For actual separated flagstones, there's also "no need to prevent it, they flex at the joints." But mostly drainage.
    – Ecnerwal
    Apr 8, 2021 at 18:15
  • Thanks. What is the usual thickness of the drainage layer?
    – r13
    Apr 8, 2021 at 18:18
  • @Ecnerwal That's a good point, about the pre-cast paving stones being 2" thick. I guess I assumed they would somehow better made than whatever I create with concrete mix in a hole in the ground ;) I suppose I need to do more research on the different types of concrete locally available. Apr 8, 2021 at 19:26

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