Isolation stones useable??

[atak]

Goodmorning, after selling our house I want to built a Pizza oven again in our new house.
It will be a napolitan oven again.
My question: I have 100 isolation bricks laying here, can I use them as under floor for the pizza oven built? or are they to soft to built a oven upon them.
Thanks, Adrian.

[UtahBeehiver]

Insulating fire bricks (ISB) will work as insulation under the standard fire brick floor. Typical ISB have a thermal conductivity value of 0.15 W/(km) vs 0.05 for CaSi board. Not quite as good as CaSi but if you have them use them, they are typically very expensive, use what you have, turn on edge if you want more thickness and insulation since you have a 100 you have plenty.

[atak]

Thank you very much for the answer, so I can build the whole dome on it? , Adrian

[UtahBeehiver]

No on dome only under floor bricks, they are too soft and cannot handle the abrasion and will not store heat,

[rsandler]

To elaborate on Utah's comment, the sequence of the structure, from bottom up, needs to be:
1. Concrete stand
2. Insulating Bricks
3. Dense firebrick floor
4. Dense firebrick dome
5. Insulating layer (CF blanket, perlcrete, vermicrete etc.)

That is, assuming what you have is insulating firebrick, they aren't going to crumble under the weight of the dome, but they aren't suitable to be an exposed surface for multiple reasons. If you want to double check that what you have is stiff enough, just try standing on one of the bricks. Despite the large overall weight of a brick oven, the pressure on the floor/insulation comes to around 2-3 pounds per square inch (PSI)--rather less than from a typical adult human standing on one foot.