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

[Bernhard Masterson]

Hi Brian,
  From my experience it is a safe bet that your moisture issue is condensation. Especially if you see droplets of water on the urbanite.  If it were wicking water it would merely be damp.  Solutions are insulation, especially exterior, increased air flow and air temperature to raise the relative humidity and temperature of the wall and urbanite above the dew point.  Because concrete is crystalline in nature it is a far better conductor of heat than amophus cob.  This means that the urbanite is conducting heat out of the cottage which results in lower temperatures of the urbanite on the interior.  
   Insualtion options are ridgid foam (most insulative and durable), hemp lime or sawdust lime mixes.  Hemp lime actually foams slightly as a result of a reaction between hemp and lime.
Ensuring that the exterior soil is as dry as possible is also a prudent action to take but not likely your primary issue.

- Bernhard 



Get under a sustainable lifestyle umbrella, the carbon is going to hit the fan.

____________________________________http://bernhardmasterson.com

Natural building instruction and consultation


> Message: 1
> Date: Mon, 24 Jan 2011 14:43:52 -0600
> From: Brian Liloia <evacindustry at gmail.com>
> Subject: [Cob] Mysterious foundation moisture issue -- rising damp?
> To: coblist at deatech.com
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> 
> 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 40? in some spots (the NW corner), according to an infrared
> temperature sensor. (The walls are about 53? 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 60-65? 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