Cob building shrinkage

[Mike Carter and Carol Cannon]

We saw some shrinkage in our 15 foot walls.  There seemed to be two factors:
the amount of coarse sand in the mix (more sand = less shrinkage) and the
speed with which we built (more speed = more shrinkage).  As recommended in
the various cob books, we stopped to let the walls dry a bit before putting
on the lintels.  Once there is a dry crust (1-2") on the outside of the cob
(a couple of days here in Texas), it is safe to put on the lintels if they
rest on the dried parts.  The same is true for embedded flooring and beams.
Window bucks should be braced to help them keep their shape, anyway.  The
lintels should protect them.

In one place, we had a vertical run of conduit that was cobbed over very
fast.  It was right next to the wall and actually popped out 1/2" due to
compressive pressure from shrinkage.

Arches are very handy for eliminating lintels.  But we have 10 feet ceilings
partly to accommodate the arches.

Mike Carter & Carol Cannon
cobcrew at sprynet.com
http://home.sprynet.com/sprynet/cobcrew
Austin, TX    USA
-----Original Message-----
From: Anthea & Tracy <mummles at island.net>
To: Coblist <coblist at deatech.com>
Date: Thursday, January 28, 1999 1:03 AM
Subject: Cob building shrinkage


>I have noticed that log house builders leave an insulated gap above
>door and window frames to allow for structural settling and shrinkage.
>Does cob shrink much as it cures? Has anyone had a problem with
>windowframes or lintels being pulled out of skew as the building
progresses?
>
>Tracy
>