[GSBN] Herbert's recipe

[Andy Horn]

Hi Bob
To answer your questions:
1) Yes to answer your question I have used it on 4 different projects so far
and always with different clays ....
The most of it is the earth that is the same earth that is being used in the
walls either to pre-coat bales or in the making of mud brick or cob
walls.....but Herbert added approx 20-30% of a stronger clay to the earth we
used in the heritage project with earth bricks where the earth/clay was
quite weak really....he said it depended on if there was enough clay in the
soil ...because only/mostly the clay floats out into suspension leaving all
the gravels, sands and silts behind one would have to clean out the clay
water bath too often if the soil used did not have much clay.
I suppose there is still some variation in the clay percentage ....but due
to the separating out of the clay I suppose the mix is much more consistent
really despite different clays....In addition, I suppose you are starting
with a clay soil that you have already figured out is stuff that can be
built with.

2) We painted/splashed on the slip with a block brush. It's the same as
wetting with water just before your apply the plaster, but one uses clay
water rather. Herbert described how the clay acts as a kind of expansion
joint between an older and newer layers,fusing the old and new together to
help avoid a cold joint......I have not experimented myself extensively on
this finer detail....however, interestingly it was a finer point that
Herbert was quite particular about.

cheers
Andy

-----Original Message-----
From: Bob Theis [mailto:bob at bobtheis.net] 
Sent: 20 April 2011 11:14 PM
To: Andy Horn
Subject: Re: Herbert's recipe

Andy,

Many thanks for this, it's a very tantalizing blending of materials.   
And your paper is exemplary for its clarity.

Two questions:
1. Bill Steen is always cautioning that the success of earth/lime  
mixes depends hugely on what sort of clay you have. Have you done  
this with several sources of clay?
2. I'm fascinated by the wetting of the wall with clay slip.  I would  
have thought that a layer of pure clay on the wall would compromise  
adhesion of the subsequent plaster. Do you brush the slip on, or  
spray it ?

Thanks again,

Bob Theis