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Re: GSBN:Jeff Ruppert and clay tests

A few confirmations from the Bill and Harry fan club:

the silica in the clay begins to break down into gel and recombines with the calcium to make a new substance that is stronger and more water resistant the original clay. Then, instead of modifying the clay, it truly becomes a "stabilized" material. The key is adding enough lime, anything short of that makes it weaker.

I believe I have touched this gel with my own hands. I mentioned in an earlier email how, when you are addng lime to a clay plaster, there comes a point where the mix stiffens tremndously and turns "greasy." When you add more water to this mix, which you need to do in order to avoid burning out the mixer and also to be able to get the material on the wall, the plaster does take on a gel-like quality. This is also what makes it slip nicely through the hose on the pumper, and work smoothly with the trowel.

And from Andre:
Observing the traditional lime/earth plasters (and a traditional digging
site) in our region (above Bordeaux, France) leads me to believe that they
used very silty soil containing a lot of gravel (up to 6mm).

Oddly, the hardest, most crack-free lime-stabilized plaster we have made was with a very silty soil, so silty that it would not have made any sort of suitable plaster without the lime. (Adding the lime was something of an act of desperation- I showed up to lead a work party far from home, and found that the reputedly excellent clay was mostly silt.) I was very surprised to return a year later to find that the plaster seemed more durable than what we usually make at home.


Paul Lacinski
Amy Klippenstein
GreenSpace Collaborative
Sidehill Farm
PO Box 107
463 Main St.
Ashfield, MA 01330 USA