Cob Re: Particle Size Distribution

[M J Epko]

At 08:23 PM 10/21/98 +0800, you wrote:
>It is important to have a balanced mix, so checking the particle size 
>distribution is important.  Over 20% (approx) clay and you can expect 
>shrinkage, and over 30% (approx) big shrinkage, and over a longer time 
>period. Besides, the higher the clay content, the harder it will be to 
>work!

	Depends. Pete Fust's been successfully using the local soil (virtually all
clay and silt) here in Kingston, NM, to make "tractor cob" without adding
sand for the last couple years. (Scratch up the ground, throw down straw,
squirt on some water, drive the backhoe over it a few times, scoop it up in
the bucket and drop it a couple times. Not particularly soulful, I'll
admit, unless a person's really into backhoes like Pete is.)

	Contrary to just about everything that ever gets said about how the best
way to make good cob is with fixed percentages of sand and clay and straw,
this no-measure stuff is impressive. There are other sand-added cob
structures on the grounds (a Kiko Denzer horno, a Cob Cottage Company wall,
etc.,) but the stuff Pete's been doing seems to be standing stronger and
erodes much less significantly than sand-added mixes. Most surprisingly,
there isn't significant cracking.

	I think it's important to read the books and know as much theory and as
many generally-successful practices as possible; I also think it's
important to then throw out all dogma (not the lessons) and learn one's own
back yard without words, using things like hands, feet, eyes, nose, and heart.



   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   Freewheeling autonomous speculation - Think!
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    M J Epko - duckchow at mail2.greenbuilder.com
               Kingston, New Mexico
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    I have found the best way to give advice to 
    your children is to find out what they want 
    and then advise them to do it.
      - Harry S Truman, television interview 
        (interviewed by his daughter, Margaret)