This is also something I've been wondering about too.  Here in Ontario we do not have typically have the temperature changes like you do in the west, but I've am curious about the long term effects of these temperature changes on cob.

My short term plans is to build a small cottage like house as my first cob project so I can get a feel for it and learn a thing or two before trying something bigger.  I am curious what the side effects could be in a house that sits unheated for several months in the winter.  If I were to heat it for a weekend or something like that, could this cause excess moisture to condense on the wall softening the plaster?  Could this cause the plaster to separate from the wall?  Would it even be possible to heat the place since the walls would retain so much cold anyway?

I fully expect that a cob wall will need continuous maintenance in some form or another, but could this change in temperature make it unpractical to build with?  One positive point for me is that there is a cob church that was built in the early 1800's just down the road from a potential building site I've selected.  I'll have to go over and see it one of these days to see how it has with stood the test of time.

Jason
Toronto, Ontario

From: Tom Fetter
The stumbling block in my mind has always been how to adequately protect an external earthen plaster from cracking/spalling in the repeated freeze/thaw 
cycles we regularly have at either end of the winter.  Through November, and then again for about 7 weeks in early Spring, we often have humid days (as snow/ice melts) and freezing nights.





