Stone fire pit

I would very highly recommend using one of them steel elevated firepits in this case, such as the type below. If you are at all worried about the surface underneath, this is the only way to go. The heat of the fire and coals, along with the moisture in the natural stone or mortar will definitely crack the stone, and the stone may even “explode” if it gets too hot or is too wet. I’ve seen this happen many times with campfire rings made out of natural sedimentary rock. Even the retaining wall block fire pits should be lined by a steel ring a smaller diameter than that of the stones. This creates a thermal gap to prevent them from cracking and “pinging” aggregate everywhere. I cringe when I see them build these tiny little firepits out of face brick on HGTV not realizing that they may explode and cause serious injury.

If you must build a stone fire pit, make sure it has a steel liner with an air gap, and you may want to consider a steel bottom separated with legs, refractory (fire) brick, or sand. You could also build the bottom and sides out of refractory brick if it is a more permanent installation.

Beyond a fire barrier I imagine that you need to know something about the stone used in the patio and it’s reaction to heat. You may keep it clean but can you be certain you won’t crack it or cause it to discolor?

Same situation. aby concrete is porous and will hold water…so it isn’t fire resistent and will crack or spall apart, sometimes violently. You can get these elevated models with grates in them to keep the fire off the metal base and allow coals to fall below., and you really don’t need too much air underneath unless you plan on doing some blacksmithing. The air will find it’s way in. You can always get one of these metal thingies and just build your block wall around it so it LOOKS permanent. And they come with an flying ash catching screen, which is always a good idea unless you are really out in the oprn. I would not place unsheilded fire around any concrete product, period.