Stone fire pit

[Bill Edwards]

I’m building a fire pit using natural stone on an existing stone patio. Any ideas on what to use to protect the original patio in the bottom of my fire pit?  I’d rather not use sand.  I’d like a more solid, stable base to put a fireplace grate on and to make it easier to clean out.

Thanks.

[Jason T. Radice]

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.

[Bill Edwards]

Thanks, Jason.  I don’t like the elevated fire pits because of having no air flow beneath the fire.  I would prefer to use a fireplace grate inside my firepit (which is ringed with retaining wall block).  What about putting 1.5 inch thick concrete square “stepping stones” underneath the grate to protect the original patio?  Thanks again.

[Rob Halpern]

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?

[Calico]

If you are concerned about your existing patio, do not put a fire pit on it. Locate the fire pit adjacent to the patio (preferably downhill and downwind from the patio), draining someplace that can filter wet soot, bbq grease, etc. A fire pit in the middle of a patio as seen on HGTV should be connected to a subsurface drainage system that daylights to an out-of-the-way place in the landscape (and not to or near a creek or pond).

Also, consider the weight of your fire pit. Confirm that your patio and subgrade are strong enough to support it without cracking or heaving. Most residential – and even some commercial – patios in this area are flagstone with minimal base & subgrade preparation. They barely support furniture, but definitely not a decently sized fire pit.

Don’t use stepping stones or clay pavers where they will be exposed to heat. This includes the base. Use refractory brick and mortar as Jason noted above.

[Jason T. Radice]

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.  

[earthworker]

Any good stone/masonry fire pit will incorporate fire brick and refractory mortar.  This is your best option for limiting the radiant heat from a fire.  Do a  web search on it and you will find what you need.

[Bill Edwards]

Thanks everyone for all of the great suggestions.  I think I’ll go with a steel fire ring inside my stone fire pit with fire brick (if I can find it 🙂 or sand on the bottom to protect the existing patio.  Thanks again, lots of good knowledge on here!

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