Vapour Barrier

[Tim Castle]

Will:
Thanks for your response.

Will Firstbrook WCB of BC wrote:
> Mexican adobe structures that were covered in a plaster in order to
> restore them actually cased significant damage. As it created a vapor
> barrier that caused deterioration inside the wall. My understanding is
> that cob needs to breathe. It can absorb quite a bit of moisture and
> pass it through the wall. Sometimes vapor barriers cause more problems
> then they are worth.
right... the kind of thing I'm concerned about; I don't know how much
moisture per day/month/whatever a household gives off, and consider that
by spring a winter's worth will be frozen somewhere in the wall... which
by the time it is cured, and has frozen in the fall would be extremely
dry on the outside, and very (?) moist in the middle somewhere -- ie.
big moisture differential.
> 
> One could turn the question around, what is the benefit of a vapor
> barrier? I thought the main benefit is to eliminate /reduce drafts thus
Certainly drafts are nasty when it gets cold enough, but my concern is
structural: if frost can heave a concrete basement wall, will it push
apart a cob wall from the inside out?
> I am attending a Cob workshop next week and I will try to get an opinion
> and some advice on these questions.
Great! Let me know what you find out.  I am planning to go to a
workshop, too, but only if cob is an appropriate building method for our
climate!
        -- Tim