Cob: Portland cement stucco

[BOB LUITWEILER]

As I understand it there is another source of cob-softening-moisuture
besides cracks in the Portland stucco.  When the house is warm inside
and the air outside cold, the water vapor in the warm air passes into
the wall until it reaches the dew point temperature.  That is the
temperature at which the air can no longer hold all its moisture. (Cool
air holds less moisture then warm air)  At this lower temperature the
air in the wall turns some of its vapor into water, condenses it in
other words.

If the adobe or cob wall has an impervious surface the moisture can not
evaporate to the outside,  through it,  and it becomes trapped in the
mud and builds up softening the wall until the surface crumbles off.

Bob Luitweiler