Thank you for your quick response!
Originally posted by SableSprings
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Ok, so perlite and vermiculite insulate well but don't retain heat. Is the retained heat what cooks your food from above? If I would replace the inner dome material with refractory cement or homebrew, the problem in my design would be fixed? Can I still cast this material over an exercise ball?
A cast oven (2" thick) is normally done in sections because of the weight. The hearth needs to be able to support that weight as well. Wood bases such as in your design can work but the top slab is generally recommended as 4" thick reinforced concrete. A base barrier/drain system separates it from a layer of insulation such as CaSi board or 5:1 (perlcrete or vermicrete: cement). On top of that insulation lies your oven. Either ceramic batting or 10:1 insulating cement (again either perlite or vermiculite:cement) is recommended. Most builders apply a stucco type render over that outer layer as well as trying to waterproof as much as possible since most insulation materials will rapidly absorb water (making them useless as insulation).
Also in your oven entry, you'll want to create a reveal. This allows you to seat a door so you can "seal" the oven for retained heat bakes such as bread or roasts (and many other things ). We're here to help you as much as possible based on lots of experience from the forum community... So again welcome & please invest time reading & learning through the experiences of other builders.
Cheers
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