this post was submitted on 28 Jun 2025
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Advice for fire pit construction (lemmy.dbzer0.com)
submitted 2 days ago by h0rnman@lemmy.dbzer0.com to c/homeimprovement@lemmy.world
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Hey all. I'm building a fire pit for my back yard and I'm looking for recommendations on what kind of rock to use.

My pit is going to consist of 2 concentric metal rings, one at 48" wide and one at 36" wide, leaving a 12" gap between them. I'd like to fill this gap with some kind of rock (and maybe cap it with flagstone) but there's not any good information about what kind of rock is ok for that purpose.

I understand that for the base, I'd want to use either sand or lava rock, and if i was just surrounding the inner ring I'd need heat bricks or something similar, but I'm stuck on what can go between the rings without worrying about explosions.

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[–] user134450@feddit.org 2 points 2 days ago (1 children)

do you want natural rock or is synthetic also ok? also do they need to be resistant to freezing water as well? its not clear if there will be any kind of roof above…
very conservative answer would be something like granite, diorite or similar dense rock. if you have protection from water you can also use more porous rocks like sandstone.

[–] h0rnman@lemmy.dbzer0.com 1 points 1 day ago (1 children)

Either is fine, I'm trying not to break the bank on it though. The pit will be outside, below a high canopy but not covered/roofed. I'm also not sure where I'd even find some of the more esoteric rocks. Would chipped marble work here?

[–] user134450@feddit.org 1 points 1 day ago

marble is less resistant to heat but might work if it's not directly in contact with the ambers and a little away from the fire. Chemically it is CaCO~3~ and if you heat it enough it will start to decompose to CaO and CO~2~ and crumble. It is a similar process to what you would see in a cement kiln :); not exactly stable but also not dangerous if it happens outside.