[Cob] Re: cob stoves & light straw

[Barbara Roemer and Glenn Miller]

Brad,

My cob oven gets over 700 degrees which is enough to harden but not quite
vitrify my clay.  Keeping in mind that clay bodies' vitrification temps
differ, and that my red clay is pretty low fire, I'd say the inside of any
oven is likely to be less than fired.

Your second question is harder to answer, and Amanda's reservations are in
order.  The Fox Maple post echoes what Robert LaPorte of Econest says, but
when I posted that info on the SB listserv with a query about it (seemed way
too high to me), folks reminded me of the very low R value of earth, the
extremely variable density of light straw/clay with the mix often varied
depending on whether the cobber wants more mass or more insulation, the
variability in compaction, and the unknown R value of interior and exterior
plasters, and concluded that the R value of a 12" light straw clay wall is
more likely to be half of what's claimed.  Having been in several light
straw clay buildings which were very comfortable in our climate with its ~
5000 degree days, both heating and cooling, I think the R value of such a
wall is as complicated to figure as that of a log wall.  That is, the system
seems to function much better than simply adding the elements would produce.

Barbara in the Sierra Nevada Foothills