Cob Swauna (sweat:sauna)

[John Schinnerer]

Aloha,

In his cob oven building book, Kiko Denzer notes that the outside of an oven should NOT be moisture-sealed (with mortar, etc.) because the moisture from the food will slowly accumulate in the cob, since it can't escape through the moisture barrier.  Eventually the cob will be fatally damaged by the moisture accumulation...so however you shelter your swana (giant cob oven) from rain, it appears best to use a separate roof structure of some kind.  
A for firing it, cob is only 10% - 30% clay, and the clay is dispersed throughout the mix of sand and straw - so it seems very unlikely that any explosions would occur, since no lumps of clay big enough to contain an air bubble of their very own would be present.  The lack of explosions in cob ovens tends to support this - they don't get up to kiln temperatures, I suppose, but they get plenty hot when they're being fired - up to 600 degrees at least, according to Kiko's information.  I've never heard of one blowing up...:-)

John Schinnerer
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