pumice stone vs vermiculite; clay vs brick

[mieno]

Hi
Just about to start the vermicrete insulation layer and wondering if anyone has ever used pumice stone instead of vermiculite? I have enough pumice to do the hearth but was wondering about its insulative properties compared to vermiculite - same or worse? The particle size vary between 10 - 30 mm and it is hard compared to vermiculite so I guess the slab would not be spongey like vermicrete.

Also, out of interest has anyone had any experience with clay / earth ovens? How well do they work compared to firebrick?

Thanks.

[gjbingham]

No help here. I'd expect that pumice would work OK, but if I could find ceramic board or vermiculite, I'd do that.

The less insulation you have under the floor, the faster the oven floor will cool, or the harder it will be to get hot, which will likely result in lower temps to cook your pizza on.