Dome concrete mix / fire brick thickness

[sterobloc]

I propose to build a pizza oven constructed using Perlite concrete for the dome and fire bricks for the oven floor. Two points of interest:
(1) I have read online various mix ratios of Portland cement and Perlite and mention of including fire clay and lime into the mix. Any advice for the inclusion of fire clay and lime? Also should I use ordinary Portland or high temperature fire cement?
(2) For the oven floor is it better to use thicker 64mm or thinner 32mm fire bricks? As I see it the thinner will heat up quicker but the thicker will absorb and give out more heat longer.
Thanks.

[UtahBeehiver]

Typically, Pcrete vor Vcrete are insulating layers over a dome of dense refractory concrete or firebrick. I suggest you do a search on the forum for cast ovens or look at postings by David S.

[david s]

The I have heard of some folk using perlite or vermiculite in the mix for the inner layer and reporting that it works. I would not recommend it though because it makes the resulting casting much weaker leaving it subject to abrasion damage. In addition because it is an insulator it will make the casting resistant to heat (lower thermal conductivity),making it difficult to heat as well as having a lower thermal mass meaning it won't store much heat.
Regarding the floor, you need around 2" of floor thickness to store sufficient heat in the floor so use the thicker floor bricks, 34 mm not enough.
Do not use lime in conjunction with calcium aluminate cement as it acts as an accelerant and you'll find the brew goes of before you can place it. The best would be a dense proprietary castable refractory from a refractory supplier. You can use the homebrew, it works, but it's not as good although much cheaper.

[Allie]

This is what I hoped to do because the brick dome is just too much for my skills to handle. I plan to do vermiculite /refractory cement for dome and refractory brick floor with the ceraboard under it. My concern is the floor will get so hot the dome won't be able to withstand the heat and blow out or up! Is that possible? Can these materials work together? I know it won't heat as high as a brick oven..I just don't want a fire or blow out. Pls advise before I continue. Thanks in advance.

[david s]

The homebrew mix I referred to is 3 parts sand, 1 part Portland cement, 1 part hydrated lime’ 1 part fire clay,, by volume, mixed with water to a stiff trowellable consistency.This is a far superior mix IMO than one containing either perlite or vermiculite for the reasons I gave in my last post. It does need however to be insulated over and that is where you can use either ceramic fibre blanket, Rockwool, perlicrete or vermicrete.