Stabilization of first 6 inches

[mey.er at mail.utexas.edu]

>Can one use cement-stabilized cob for the first 6 inches above
>ground?  Will a cement, sand, clay mix withstand humidity and frost?
>Can I use this mixture instead of a course of rock?  Actually could
>adobe bricks be made of this mixture and used as the first course?
>
It may have been done before, but I'd be cautious.  Clays are usually high
in sulfate content and portland cement does not respond well to sulfates.
In the presence of water, damage known as sulfate attack can occur.
Concrete crumbles when this happens, has to do with internal expansions.  I
would assume the same could happen with cob, provided it gets wet.  Water
is the substance that sets off the reaction.  An interesting experiment
(provided you have the time) would be to make some brick with your intended
ingredients and soak them with a hose every few days until damage occurs or
your satisfied that the mix is stable.  If the cement content is kept low
there may be no problem. Interesting question,   Chris Meyer