Cob: RE: RE: Posts embedded in cob

[Shannon C. Dealy]

On Thu, 2 Nov 2000, Firstbrook, Will wrote:

[snip]
> Regarding your design, my understanding is the cob should start approx. 2'
> above ground at least on the exterior so no water can be wicked up into the
> cob. Also the foundation that cob sits on should ideally be rough so the the
[snip]

Actually, preventing wicking is not a matter of height, a one inch above
ground foundation with a waterproof barrier in it could do that providing
no standing water around the structure ever reaches the height at which
the water proof barrier is located.  Wicking through even a quite short 
concrete or rock foundation (without added water proofing) is unlikely to
have any effect on a cob wall unless the foundation is in standing water,
and possibly not even then.  The main reason that I am aware of for the
high foundation is that when rain hits the ground (or plants or other
objects near the base of your wall) it splashes onto the wall and can/will
cause errosion in your wall.  I have seen this effect on a couple of cob
structures (I actually stood out in the rain watching it for a while) and
was surprized at how much greater the damage was from the rain hitting the
ground or bushes and splashing the wall than it was from the rain which
hit the wall directly.  From what I saw, rain hitting the wall directly
was minimal (due in part to the roof overhang) and tended to be absorbed
into the dry cob wall (rather than running down and erroding it), but of
course there was lots of rain hitting the ground and bushes around the
base of the buildings, and run off from the roof (which had no gutters)
greatly added to the water hitting the ground all around the perimeter of
the building.  The combination of rain and run-off caused the base of the
wall to be splashed continuously up to a height of a couple feet leaving
the base of the wall looking quite damp even a couple days after the rain
stopped.  There were also small but easily visible errosion tracks running
down the surface of the cob that was located within 1-1/2 to two feet of
ground level.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
                      |    Embedded Systems, Real-time, Device Drivers
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