Berkeley Cob Project

[Paul & Mary Salas]

Otherfish at aol.com wrote:

> 
> one of the beauties of cob as a concept is to work as much as is possible with
> locally available materials - if natural pozzolans are available then no
> problem
> -if not then what......  hmmm

Absolutely correct--locally available materials.  Here in N.M. we have
limestone, gypsum, cliche, tuff, ash, pumice, slag and even excess
amounts of flyash as available pozzolan materials. In other areas of the
country similar materials are availalbe--get creative.

 
> fibers?
> have you tried micro fibers in your work might work well with your "maquina infernal"
> the idea being again to devise ways to strengthen the earth matrix with
> natural material available locally

No need if the base mix design remains proportionally constant and clay
content remains below 25%.  Test samples usually prove out the need to
add fiber or not. I will be running tests with fibers mostly to validate
the "maquina infernals" ability to handle the material.

> re the dreaded STUCCO
> it really is a problem to put impermiable finish layers on earth walls
> it will trap any moisture that gets into the wall - in the wall
> -wrong place
> -stucco actually does more harm than good in earth structures
> -this is a proven fact
> 
> the wall needs to be able to breath
> just like us

Unfortunately in many areas the "CODE" requires a stucco application. 
Agreed that any cementious material on a abode/cob/earthen surface is an
invitation for future problems and definately a trap for moisture and
water. The primary reason for failure is that the two materials do not
bond together.

Once the adobe/cob/earth material has fully cured/dried there is no
breathing in the base material or condensation as in strawbale. The
problems arise from the porous nature of the stucco itself and the
separation that takes place between the stucco and earthen base
material. This in turn leads to a total failure of the stucco coating.
The key is to keep "ALL" moisture, vapor and water out of the wall as a
detail component in the building process.

> have you thought about this with your waterproof earth render?

Yes--in fact I have to pre-wet the earthen surface to about 1/8" as the
waterproof render actually soaks in, penetrates and bonds with the
earthen base material. In samples I have worked with, when an attempt is
made to separate the render from the base material, the break occurs in
the base material at a depth of 1/4 to 1/2". In thin test pieces where I
have deliberately broken the sample, I have been able to rejoin the
pieces and they appear to "heal" and when broken again, you can't tell
where the old break was. This is a major break-through because when a
building settles and cracks occur, stucco cracks remain and will
continue to mirror through into the future. This material gives us an
opportunity to make a repair that actually works. 


Paul Salas
SANCO Enterprises
Albuq., N.M.