Cob Re: How long does cob have to cure?

[Shannon C. Dealy]

On Sun, 15 Mar 1998, Michael Saunby wrote:

[snip]
> > No this is not true.  I can take a year or more for a cob wall to dry, but
> > this is how long it takes for the moisture level to stabilize.  It doesn't
> > actually fully dry, there is always some moisture content, and it will 
> > vary depending on outside temperatures, humidity, rain exposure, etc.,
> > just like with wood and pretty much any other porous building material.
> > 
> 
> An architect here in Devon told me that someone caused a cob building
> to collapse by using an injection damp proof treatment in the supporting
> plinth.  The slow movement of moisture through a cob wall is clearly
> very important to its stability.
[snip]

Slow movement of moisture through the cob will not harm it, accumulation
of large amounts of moisture in one area however, can significantly weaken
it.  During normal cob construction (i.e. no experimental techniques), you
CANNOT build the wall faster than it can take the weight structurally
without the wall giving you plenty of warning that you are going to fast
(bulging of the lower wall area).  In order for a cob wall to collapse
after it is built, it would require that either the design of the wall was
structurally unsound to start with and you were lucky to get it up in the
first place (like building an unsupported wall at a 45 degree angle :-) or 
the wall is not adequately protected from moisture and begins to 
accumulate moisture from standing water and/or other sources.

Shannon Dealy
dealy at deatech.com