Cob: Insulation

[Shannon C. Dealy]

On Wed, 6 Sep 2000, Patricia L. MacKenzie wrote:

> Here goes - my question relates to sealing of unwanted openings. I'm given 
> to understand the incompatibility between the old and new cob or between 
> cement and stackwood, shrinkage is mentioned. If the new is incompatible, 
> what is the suggested material for cracks, repair or fill in?
[snip]

For patching/attaching new cob to old, it depends on the situation, but
the key is to thoroughly wet the area to be attached to (allowing some
time for the water to soak in), and prevent shrinkage in the new cob being
applied - high sand mix, low water content, applied in thin layers.  For
small cracks the above approach should be sufficient, for larger holes,
you could  make a cob "brick" slightly smaller than the hole, allow it to 
dry (so it is done shrinking), then place it into the hole and cob it into
place as you would for filling in smaller cracks.  In place of the cob
"brick" some people will use regular bricks or rocks and cob around them.
For more serious holes (like when you have decided to fill in where an
old window used to be), I like to chip some holes into the old cob to
provide some mechanical keying of the new cob to the old, then after a
thorough wetting of the old cob, initially build up the fresh cob slowly,
then once you have a couple inches layered up and it has had some time to
dry a bit, start building up the cob normally.  For patching a larger
overhead crack (where the cob doesn't get any support from below), you may
find it necessary to drive some old nails into the existing cob (leaving 
the heads sticking out a little way so the new cob will encase them) in
order to provide support and a better bond between the new cob and the
old.

Shannon C. Dealy      |               DeaTech Research Inc.
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