Cob earth plaster test data plea

[Will Firstbrook]

Hi Robert,

The Cob Cottage Co. has a book called Earth Building and the Cob Revival: a
Reader. In it is a reproduction of some documents from Devon England for
Repair and Maintenance of English Cob buildings. One section is titled
"Appropriate Plasters, Renders and Finishes for Cob and Random Stone Walls".

It talks about how Portland Cement-based renders damage cob and stone walls
as it restricts movement and breathing. When the renders (stucco) crack rain
water enters wall.

Lime based materials allow the walls to 'breathe' and move. They adheare
much better to cob and weak brick or stone and they produce inherently
softer and more porous finishes than portland cement based finishes. Lime
based renders acts like blotting paper absorbing and releasing moisture
relitivly freely. Also small cracks may be closed by redeposition of
soluable material from the lime.

This document does have some recipies and a lot of time tested proven
techniques but does not have the actual numbers (scientific data).

I hope this helps.

Regards, 
Will  
>
>Robert Bolman
>888 Almaden St
>Eugene, OR 97402
>541-344-7196  /  email: robtb at efn.org
>
>I'm building a straw bale house in Eugene, Oregon – a place known for lots
>of gentle rain.  I'm presently permitted to put cement stucco on the
>exterior of the building and a commercially produced plaster product on the
>interior, but I wish to change it all to some form of earth plaster
>probably finished off with a coat of lime plaster.  
>
>My building department needs some good information.  They need testing data
>on earth plasters taking into consideration variations in clay
>expansiveness.  They need numbers.
>
>Any suggestions that anyone could offer would be greatly appreciated.
>Sincerely,
>Robert Bolman
>
>
>