Brick selection

[Bill003]

I have very light firebrick that was used in ceramic kilns, I was planning to use those to form the floor of my oven. They are soft. Can I do a thin layer of refractory mortar 1" or so thick over them? I was using a mix of 3 parts sand, and 1 part of each lime, Portland cement, and fire clay.

[UtahBeehiver]

Soft fire brick (aka IFB) are for insulation only. They are NOT suitable for the floor or the dome. These need to be dense fire bricks. That said, IFB could be used under the dense fire brick floor for insulation. Dense fire bricks will saturate and store heat from the fire. IFB prevent or reduces the heat storage from transmitting away. The floor will expand and contract so 1" refractory mortar will crack and it not recommend for floor anyway. A min brick floor thickness needs to be at least 2.5"