Oven floor question

[LanMan]

This is my first attempt to build a WFO. I am building a 36 inch dome. Under the oven floor I have 2 inch FB ceramic insulation board. The floor is 4x9 fire brick. My question is do I need to use mortar to set the oven floor brick on the FB insulation or just dry lay them on?

[jonv]

The floor can be laid directly on the board. If they are not sitting quite flat the usual method is to use a thin layer of sand and fireclay, spread with a notched trowel. Do this dry if you can, as the insulation will suck up any moisture and it takes a while to drive it out later. Otherwise mix to a thick paste - I found it easier this way, but dry is ideal.

[LanMan]

Thanks for the answer. The oven floor is very level in my case. Looks like I can start the dome build today.

[SableSprings]

When I laid floor bricks down over a perlcrete insulation pad and tried the dry sand method for leveling, it didn't work well for me...bricks would move too much as adjacent bricks were set. A fairly light misting of water over the sand/fireclay topping helped immensely. The ridges from the notched trowel held much better, the moisture firmed up the sand mix considerably (so adjacent bricks stayed put), and the light top misting didn't add enough water to wet the board or affect the curing process.

A very thin layer of mortar along seam lines of the insulation board will keep sand from trickling down over time and creating small "empty pockets" under the cooking floor...obviously a minor point, but over the years it will help the floor from getting "bumpy" from the hourglass effect.