[Cob] Silverfish, Tornadoes, and Humidity

[Shannon C. Dealy]

On Thu, 17 Mar 2005 CarmenKittieCat at aol.com wrote:

[snip]
> potential problems with termites and silverfish. She offered  a suggestion for
> preventing termite problems, but then went on to describe a  problem someone
> has with silverfish, and she said she knew of no "nontoxic"  solution. How
> common is the silverfish problem and has anyone yet found a  nontoxic solution to
> the challenge?

While there are silverfish and termites in this area, I haven't had
problems with either one so far.  I think for silverfish if you eliminate
damp areas and have a tight house, you eliminate both the attraction and
anyway for them to get in.  Termites might be more problematic, but I
think they also tend to like at least moist earth, so once your walls are
set, if you can keep them dry, they are likely to find more hospitable
places to burrow in.

> And then, what about tornado resistance? Given that the roof might  come off
> during a tornado, how would the building itself hold up? Tornadoes are  rather
> unpredictable, but generally speaking, with no regard to the potential  rain
> involved, how well do curved cob walls hold up to tornadic winds or the
> associated high winds in nearby ares during a tornado?

Curved walls are better than square (more aero-dynamic), and the high mass
of the walls would probably fare better than conventional wood
frame structures since it would require stronger winds to move and/or lift
the structure.  The rain is pretty much irrelevant, since it takes time
for cob walls to soak up enough moisture to soften significantly, and
tornados just don't last long enough (particularly in one place) for the
cob to weaken.  Of course a direct hit by a really strong tornado will
flatten pretty much anything, but if I had to be in one I'd take my
current cob house over a conventional wood frame structure.

> Finally, humidity. I have read that the cob walls are very slow to  respond
> to temperature change, etc., but I am concerned about humidity--not rain  so
> much as the "thick" air, you know what I mean, and for extended periods  of
> time. In the summer we can have weeks of H-E-double-hockeysticks where  the
> humidity drives the heat index very high, day after day. Does the  humidity permeate
> the cob walls at all? Not to mention the plaster, how  does that hold up? Can
> humidity be a problem over time, even though it's  merely one season out of
> the year?

Cob will (to some extent) moderate humidity in much the same way it does
temperature, by absorbing some of it and releasing it when the humidity
drops.  The cob won't care about seasonal fluctuations in humidity,
though your plaster might depending on what you use if the humidity is
really bad.  I would tend to go with a good lime based plaster and (if
desired) a lime based paint, as it tend to be more resistant to damage by
humidity as well as less hospitable to mold and mildew.

Shannon C. Dealy      |               DeaTech Research Inc.
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