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Re: GSBN:Jeff Ruppert and clay tests

Tim OK wrote:

We have moved to using either lime or earth
plaster or lime plaster. though we tend, like many of you to add a top lime
coat on the exterior of our earth plaster. Recently I was afforded an
opportunity take apart some of these assemblies. (more on that later) most
notably the earth to lime connection was the week link and I would assume
extreme weather would like to pop the thin lime coat off. for this reason
(and the mold that Paul mentioned) I am interested in getting a small amount
of lime into the mix and work it to the surface then scratch so that I might
have a better chance of getting a lasting bond. I have not noticed much
degradation of the brick clays but site soils do all kinds of things that I
don't fully get yet.

Interestingly, there's a parallel discussion going on in the replacement strawbale list (http://groups.yahoo.com/groups/sb-r-us) between Bill Steen and Harry (whose last name I can't remember, but his email is CALXA@...he is among the Plaster Gods) under the subject line "new group" that details exactly what is happening to cause that weak link between the earth and lime.

The short version is that too small amount of lime works as a flocculant, essentially turning your clay into silt. I think that's likely what is happening at the earth/lime boundary. You may want to re-think (or at least test on a wall you don't care about) your theory of working a small amt of lime into the surface & then scratching.

"Using too little lime increases the permability of clays by flocculation of
the clay particles.....we call this modification.... A good use here is 1 - 2
% lime on  a hard pan soil - unsuitable for agriculture.... now treated with
lime becomes friable.....and very suitable for plant growth.... "

Once you hit a certain % lime (which varies a bit depending upon the clay), you start making cement.

"I think a lime clay mix with sufficient lime so the pH is above 12 would be
fine - Now you have made a hydraulic lime........ Most clays need above 5%
lime by weight to achive this high pH level.. some as much as 8%."

"BUT ---  if only small amounts of lime are added to the clays, then I think
you have converted the clay into a silt thru flocculation; resulting in a
very permeable material...not suitable for a coating...."

Bill Christensen

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