what thickness of flagstone?

I have been researching this a lot on the net and all the searches I have done have said to use 1" - 1 1/2" flag stone for patios that will have a gravel/sand or a concrete base...

Ask any landscaper and they will tell you 1" - 1 1/2"... At least that is what they all told me...

Good luck, Mark

Its a toss up. If you have freezing conditions or soft ground, use the 4" thick. It might be a little overkill, but less likely to move around or break. (4" thickness is minimum for concrete.)

You also need to realize that you will need 4" - 6" of gravel and then 1" -

If you simply lay the flag stone on the ground, you are asking for problems...

Good luck, Mark

was thinking more of just flagstone on the expansive clay soil, with enough space between the large pieces of flagstone for grass or moss to grow

how would gravel/sand benefit that?

Maybe in your part of the country. Around the NorthEast, even the stone masons from the old country would expect to find that any "flagstone" is slate. I've never even see sandstone in a stone yard, although I confess I never specifically asked for it.

Bob

In my area it's limestone or dolomite. Guess it varies from place to place.

Flagstone isn't a material, it's a way of using the material. Any rough, flat stone used as a paving material is flagstone. Usually that will be a sedimentary rock, because that's what's most likely to come in conveniently flat slabs, but when we did the front walk at my father's house, we used mostly basalt, because the nubbles of garnet crystal gives better traction.