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

[Henry Raduazo]

Brian: My guess would be condensation. The way to solve this is  
insulation. On my walkout basement I buried foam along the footings  
of my walls, and extended this up to the cob. I then used a fill  
plaster of paper, sand and clay soil to blend the foam with the cob,  
and I painted everything, the foam, the earth plaster and the plaster  
covered cob wall with lime paint. It does not look too bad. You can  
insulate either the inside or outside surface of the wall. I prefer  
the outside in case the foam gasses off.
	The walkout basement is cob on top of cinder blocks and it felt  
oppressively humid when I put the roof on and closed the door so, I  
covered the entire floor with 6 mil plastic and put a layer of  
recycled brick tiles on top of the plastic. You could put any floor  
surface on top of the plastic.  I then painted the blocks with Kills  
water seal and painted the kills with lime paint. That cut down the  
moisture content of the air in the basement so I only get  
condensation on the uninsulated glass doors and windows. I have  
insulated glass skylights on which there is no condensation and of  
course there is no condensation on the blocks or 8 inch thick cob walls.
	I have never known concrete urbanite to conduct moisture to any  
significant extent, but that could depend on the aggregate and on how  
porous the cement was. Cement that was mixed with too much water or  
which had a light weight aggregate like vermiculite or Solite could  
of course conduct water in which case the only solution would be  
kills water seal or something like that. Kills is also supposed to  
contain a fungicide.

Ed
On Jan 24, 2011, at 3:43 PM, Brian Liloia wrote:

> 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
>
> -- 
> _________________
> I live at http://dancingrabbit.org
> and this is the Year of Mud http://small-scale.net/yearofmud
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