Cob Swauna (sweat:sauna)

[David Aguirre]

At 10:16 AM -0800 10/29/97, John Schinnerer wrote:
>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

I agree. A cob building is not likely to blow up. I've been making
handbuilt, ceramic sculptures for about 15 years now. Firing a cob house
should work fine depending on how much clay is in the mixture and what the
structure that is being fired is like.

Air bubbles, whether in ceramics or in cob need not "explode" if the firing
is brought on at a slow pace.

The expanding air/moisture in an air bubble can seep out more gradually as
long as the fire isn't too intense, too quickly. The fire and the cob need
to have a longer get aquainted period.

 Straw in a cob structure that is being fired should help the structures'
survivability, since each burned out strand of straw provides a tiny
passage for air and moisture to seep out.

David Aguirre