Making countertop cement refractory

[GianniFocaccia]

As part of my outdoor kitchen project, I am looking to build a firepit of the design below (drawn up with firebrick lining) and my thoughts are to encase concrete blocks with Quikrete countertop cement. It should be easy enough to form up, but would like to get some advice in making it refractory.

If lining with firebrick, do I (refractory) mortar the firebrick right to the concrete block?

Instead of the firebrick liner, is it possible to add a portion of fireclay to the countertop mix on the inside of the pit and skip the firebrick? The advantages of going this route is I only have to pour it once and the color remains consistent throughout. I am thinking of a concrete thickness (inside, top and outside the block) of 3".

Any/all thoughts appreciated.

John

[david s]

A fair amount of the heat you put in will wick away into the concrete bricks. You could lay a bed of vermicrete say about 2" thick to avoid the heat loss, then give it a layer,say 2" of refractory concrete. A castable refractory would be best, but a mix of 1/4" aggregate, sand, cement and lime (6:4:1:1) should suffice and be much cheaper. Have done a bit of thought on exactly the same kind of project, but never got further than a brain plan. Let us know how you go.

[Tscarborough]

You have a lot of things working against you on a project like that. Monolithic structure, inside corners, etc.

If I were going to do it for someone else (because I would not do it for myself), I would build the walls and floor of the actual pit from 5 "sheets" of (castable) refractory about 2" thick, maybe 3" for the bottom. I would assemble them in such a way that they could expand, and edge the top with a semi-embedded angle. I would also embed lifting hooks in the floor. See attachment.

If you do it like that, the rest should be alright using the countertop mix.

[GianniFocaccia]

Thanks Tom. I may be extending my abilities by tackling something like this although your diagram makes sense and I'm sure I could form five 2"-thick sheets of castable. I'm not sure I could apply the countertop mix in the short time that I have, so I may have to rethink my design.

Thanks again for your quick reply.