[Cob] Mysterious foundation moisture issue -- rising damp?

[Brian Liloia]

Hi there:

I want to share a problem that I think is rising damp causing a pretty
serious issue in my house. I have a two course urbanite foundation with
clay/sand mortar above an 18" deep rubble trench, with ~18" thick cob walls.
I'm located in NE Missouri.

This winter, about a week ago, I began to notice the infiltration of
moisture at the base of the wall inside -- some of the pieces of urbanite
have a wet look (beads of water on the face), there are wet spots on the
floor at the base of the wall, and the wall itself (12-18" up from the floor
level) is in some places damp, or even icy (really only the NW corner here),
and definitely has mold developing (a fluffy white mold that I have to
weekly spray with vinegar and wipe away).

Over a month ago in December, the mold and moisture on the walls was already
present, but now the floor has those spots of water, too. Last winter, I
experienced this same problem and could not determine what it was. But now I
am itching to determine what is wrong, because the weekly spraying with
vinegar to clean the mold is unbearable, and the whole issue is a mystery.

I have a couple of guesses. One is rising damp. Although that does not make
sense at this time of year. It's cold outside, there's some snow on the
ground (but not touching the foundation). The ground is frozen at least a
few inches down. The rubble trench should be whisking away any moisture that
gets near the house.

Another guess is that moisture is wicking through the clay/sand mortar. Last
winter, the mortar was very wet in the spring (earthworms bore through!),
but since then I've done more work around the house to divert water.

Another guess is condensation. It's very cold here, in the mid-20s during
the day, and teens at night, lately. The foundation has no insulation, nor
the walls. (All the walls are straight cob). The bottom of the wall is as
cold as 40º in some spots (the NW corner), according to an infrared
temperature sensor. (The walls are about 53º at eye height.) The coldest
walls are definitely the west and north, and these are the walls with the
greatest moisture problems. They are also least exposed to indoor air flow,
because the bed (and other furniture) is against the wall. The indoor air
temperature is about 60-65º during the day with my wood stove burning. Could
it be the temperature differential between the air and the base of the wall
causing condensation

Could it be a mix of all of these things? I have no idea and am pretty
desperate to figure out what is wrong.

Does anyone have any clues? Help would be dearly appreciated.

Thanks for your time.

www.small-scale.net/yearofmud
- ziggy

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