Cob Size Estimates

[Shannon C. Dealy]

On Wed, 28 Jan 1998, Will Firstbrook WCB of BC wrote:

> Hi fellow Cobbers,
> 
> I have a question for some of the experienced cob builders on this list.
> Based on your experience what would be reasonable size cob building to
> complete in 1 summer with 2 people working full time, 200, 500, 600,
> 1000 sq. ft? I am currently working out details in our design and I'm
[SNIP]

This would depend on the physical strength and/or limitations of the two
people, whether or not any mechanical mixing methods are used, the amount
of interior cob walls, the height of the walls, how much time (if any)
will be required for hauling materials to the site, how much site
preparation and foundation work will be required, etc..  That having been
said, I believe it is possible for two people to complete all the walls to
the 1000 square foot structure in one summer without using any mechanical
mixing, but the best way to approach it would be to first just complete
the exterior walls along with a small triangular section of each of the
interior walls where they join to the exterior.  This triangular section
will provide any butressing of the exterior wall which your design may
require, as well as giving you the best possible connection between the
interior and exterior walls.  Once this is done, you could presumeably
(depending on your design) go ahead and put the roof on and then the
interior walls could be finished any time.  To just complete the exterior
walls should not present any problems for two people in good health 
working full time for three months.

> An idea I have regarding the connections between the sections is to
> build the archway or connection then fill with strawbale as a temporary
> wall for the winter insulation. This temporary wall can be coated with a
> light coat of plaster on the outside and a thin cob plaster on the
> inside. The temporary wall can be easily removed when the next section
> is reasonably complete. Does this sound reasonable?

You could do this, but you will get stronger cob if you just build one
section and then expand out from there.  The reason for this is that if
you build two separate sections, and then try to join between them, the
cob in the first section will probably have hardened pretty thoroughly
before you start work joining them together, so you will not get as good a
bond when you add new cob to it in order to start joining them together.
Of course if your design doesn't really need the strength in that area,
and it isn't being used for roof support, you may want to consider just
going with a permanent straw bale wall in this section, since it has much
better insulation value than cob.  Most people who are planning on using
cob in a cold climate would probably want to consider at least some use of
straw bale to reduce heating requirements.

Shannon Dealy
dealy at deatech.com