"Grunff" wrote in message
...
Andrew Gabriel wrote:

Water vapour (and air) will migrate through plaster, and will
form wet areas in cold spots.

I'm sorry - that just doesn't make sense.

The plaster will indeed have a certain moisture content (as all
materials do), which will be in equilibrium with the air. No
argument there.

The assertion that this water will condense out on the pipe is
what I have a problem with. Condensation is a phase-change
phenomenon, where a large volume of gaseous water condenses on a
cold surface to produce a small volume of liquid water.

But the water present in the plaster is present as adsorbed
water. Very little will be present as gaseous water in the small
air voids in the plaster. So how is this adsorbed water, already
a liquid, going to condense out onto the pipe?

--
Grunff


Warm moist air. Cold water pipe in wall. Do the math.