Pompeii Oven Floor Insulation Thickness

[ultrasport]

I am at the stage of building my floor insulation and my plan is to use a 2" calcium silicate board and pour a 1" layer of vermiculite/portland cement mixture on top for a total of a 3" floor before laying my 2.5" firebrick in a thin layer of a fireclay mixture for setting my floorbrick.
My oven will have a 40" inside diameter cooking surface. Any thoughts with this process?

[JRPizza]

I didn't use any vermiculite/portland with my insulating board, but I think most folks that do put the board on top of the vermicrete to get the best insulation closest to the heat.

[fox]

Yes I agree with JR.
Your board should offer a very flat and even surface so there is no need to bed the bricks, the floor bricks are best left to move around a bit to compensate for expansion when heated.

[Jubilado]

I placed the floor brick onto calcium silicate board, which was quite smooth. Depending on how even you want your floor surface, you can select bricks that are closest in height, shim with dry brick swarf, or sand with diamond discs. I did a minimal amount of shimming and sanding.

Calsil board is described as humidity resistant. I placed foamglas, which is unaffected by water and hydrophobic, under the calsil board.

3" of insulation is very light imho. I have 4" of foamglas plus 2" of calsil. This is a lot of insulation by most accounts in the forum; although it is commonly said here that you can't have too much insulation. I haven't fired the unit yet to check performance.

[NCMan]

I would not recommend the 1" vermicrete layer. One reason is that it wouldn't do much to help insulate at that thickness and would have no real strength to hold together. I just don't see the need for it. I do agree that it's nice to bed the floor bricks in some fireclay, but just enough to help set them. I also like to mix in a bit of sand and dampen it just a little, then use a notched trowel to spread the mix, tapping them in lightly w/a rubber mallet. If you are cutting your floor bricks to set inside the dome walls, be sure to leave a small expansion gap. If you are setting the walls on top of the brick, no worries w/that. Best of luck to you and keep us posted!