Cob cob/adobe

[Shannon C. Dealy]

On Thu, 2 Oct 1997, Benton J. Miller and Phyllis Ramirez wrote:

[SNIP]
> My question: Has anyone ever seen a mixture of cob/adobe used
> in building? Our idea is (we are still in the planning stages) to
> use cob for the front of our home, to acieve a graceful, sculptured look.
> Then run abode down each side and along the back of the house.  The
> inside patio would be done with adode also.  How can we tie-in the
> adobe to the cob?

DISCLAIMER :-) I have no experience with this, but this is what I would do
if I were going to try this.

If it is a traditional adobe mix, then just before joining the two
different walls, I would just try drilling a bunch of 1-1/4" diameter
holes about 1-1/2" to 2" into all the exposed surfaces (top, end, and
sides) of the last 1 to 2 feet of the adobe wall, then wet down this area
several times allowing the water time to soak in after each wetting 
(this should help the clay in the brick to bond with the cob), and cob up
to and around the prepared end of the adobe wall, making the
overlapping cob layer at least 4 to 5 inches thick.  This would work best
if the prepared end of the adobe wall has alternating bricks sticking out
of the end, rather than being a smooth finished wall end.

If the adobe is a non-traditional mix using one of those asphault based
treatments, I would probably try the same thing, but I would expect that
the asphault would prevent anything other than a mechanical bond, so I
would tend to make the cob encased adobe area larger and use a thicker
layer of cob around it and then hope for the best (i.e. I would avoid it
if at all possible).

Why not just use cob throughout?  The look of a plastered cob house is
very similar to a plastered adobe.

>
> Also, the adobe doesnt seem to need long overhangs to protect it from
> weather. Why does cob? We want the standard roof of southwestern
> adobe(without overhangs), but will that work with cob? Is it all
> in the plaster that is used on the finished building?
[SNIP]

I suspect this is mostly a function of where each material was
traditionally used.  Adobe historically was used in areas which receive
little or no rain, whereas cob was used in climates with heavy rain and
driving winds.  Since the overhangs used by cob are to help protect it
from errosion due to weather, they could presumeably be cut back in
climates where rains are mild and rare, or even removed in climates where
rain is virtually non-existant.


Shannon Dealy
dealy at deatech.com