Cob Re: How long does cob have to cure?

[Shannon C. Dealy]

On Thu, 12 Mar 1998, Frugally4u wrote:

> * How long does cob have to cure before you can move in? I've read up to a
> year - is this true?

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.

In any case (depending on the outside temperatures and humidity), most of
the drying will have occurred before you even complete the wall and I
think it would be a pretty rare case where someone could complete the
walls and roof of the structure and not be able to move in immediately.
I suppose you might want to define what you would consider to be a reason
for not moving in immediately.  Structurally, there are no reasons to be
concerned, though the interior humidity will probably be a little higher 
for a while.

One of the cob buildings I worked on was started here in Oregon during the
spring while it was still raining occasionally and it got down below
freezing on the building site every night.  In spite of this, by the time
we had the walls up to about four feet high (less than a week), the bottom
foot of most of the wall was extremely hard and completely dry to the
touch.  The areas where the wall was still moist to the touch were
those that received no direct sun and received the least air circulation.
When I have worked on cob walls during the summer here in Oregon, they
were dry to the touch in a few hours and in some cases needed to be kept
covered with a tarp to keep them from drying to fast and cracking.  There
is of course still water trapped in these walls, but it will migrate out
of the walls slowly over time.


Shannon Dealy
dealy at deatech.com