Monday, January 30, 2012

Brick Oven Insulation

antique French oven
Unlike brick ovens of colonial era and earlier, modern wood-fired brick ovens seek to keep the heat of the firing as long as possible using relatively high-tech insulating materials.
vermiculite mix

The simplest of these is vermiculite, or expanded mica. These particles, easily found at greenhouse and nursery supply stores, are fireproof and full of air.  Mixing them with a small amount of Portland cement allows you to cast shapes that will provide rigid insulating barriers. I have used loose vermiculite as a final filler in ovens of mine that have a ''house" type enclosure. 'Insulcast' a Mt. Savage product, duplicates the vermiculite/cement capabilities with a controlled albeit more expensive product.

Foamglass, Fiberfax board and brick
Insulation beneath the oven needs to be rigid and strong before the first layer of firebrick for the oven floor is laid. Again, vermiculite/Portland cement is a low-cost option but this needs an additional concrete slab below it to provide tensile strength. 
Foamglass, a refractory insulator, comes 4" thick in slabs that can be easily cut with a handsaw. It is expensive but very effective. 

For the outer part of the oven, ceramic fiber blanket can be layered to any depth to provide a high-temperature barrier.

The long and short of it is: more insulation holds heat longer. If that is your goal (a 30 hour cooking window per firing) then more is better.  I've "over-insulated" the house I designed and built for myself. The result is one-fifth need for whatever fuel source heats it.  Kind of a no-brainer.

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