People often ask us about insulation for their pizza oven. If you are casting your own dome using a high temperature refractory product, or using firebrick, you should use insulation on the outside surface before applying any exterior surface material. Once your dome cures, and before applying tile, stucco, brick or anything else, you'll want to use an insulator to dissipate heat. People often use ceramic blankets for this purpose. Ceramic blankets (such as FibreFrax durablanket) can be used as an insulator over the dome. Another option is to use a castable product made for this purpose, such as Insul Cast made by the manufacturer of Heat Stop. Insul Cast has the advantage of being easy to shape and apply, and it comes in a 50 lb. bag. Apply it two-inches thick, over the dome, and let it cure properly before applying anything else. Some people like to apply a ceramic blanket on top of this, though this is usually not necessary. Insul Cast can also be used as an insulator under the hearth (made from firebrick or castable Heat Cast 40).
Insul Cast resists temperatures up to 2,000 degrees, is non-water soluble, and meets A.S.T.M. C-401 requirements for structural integrity and safety. A 50 lb. bag covers approximately 6 square feet when applied 2" thick. MyBuildingSupplyStore.com offers Insul Cast and other Heat Stop products at factory-direct prices.