[Cob] waterproofing cob

[Dognyard]

I know it's said you shouldn't waterproof a cob wall with anything other
than perhaps a lime plaster...something breathable. However, if the
house isn't completely air-tight, is there a good reason one couldn't
apply a fairly waterproof seal on the cob only on the outside of the
house, and allow the house to breathe from the inside? Any thoughts on
this? I am from Alberta, and although we can have rainy summers which
may result in some moisture build up inside a house, but in the winter,
if you don't have a humidifier in your house, the air is incredibly dry
all winter long.

Also, would the rules of waterproofing change (again, only talking about
the outside of the wall, not the inside), if the building was largely
unheated, and very definitely NOT air tight...like a shed? If one put
air holes through the wall, perhaps up near the eaves, would the little
building breathe enough to allow one to waterproof the outer wall?

Karen Clouston