Fireclay under floor? Pompeii Oven Construction Discuss Fireclay under floor? in the Pizza Oven Design and Installation forums; Referring to the layer of dry fireclay/sand mix(page 27 of the downloadable plans) spread under the firebrick floor, is fireclay ...

[CSWolffe]

Referring to the layer of dry fireclay/sand mix(page 27 of the downloadable plans) spread under the firebrick floor, is fireclay necessary, or will just sand work?
I know fireclay is more heat resistant than sand. But think about it. Heat resistant materials vs non heat resistant. When exposed to the high heat of the oven, materials such as standard brick will fail structurally. But what structural support does the fireclay give that sand could not? Sand is already broken down. It does not matter if sand cracks or spalls.
What does the fireclay add?

[dmun]

What does the fireclay add?

Fireclay makes the mixture sticky, and keeps it from sifting down into the vermiculite concrete, or leaking out the side. What insulation are you using? The fireclay mixture is just a leveling medium: if you are using insulation boards you may not need it at all.

[CSWolffe]

Sticky. Got it. Thanks.
I plan on building on an insulated hearth of vermicrete, so I need the leveling medium.