Cob: Date: Wed, 27 Oct 1999 10:45:17 +0800

[Shannon C. Dealy]

On Fri, 29 Oct 1999, Tony Palmieri wrote:

> I haven't read anything regarding what to do if your local soil is high in
> sand and very low in clay, as it is here in Central Florida. Do I need to
> import clay into the cob mix from outside the region, which does not appear
> correct to me from a bio-regional sustainability standpoint; or just forego
> clay altogether, and use the available local soil, which does not appear
> correct from a chemical analysis standpoint? What to do? Suggestions anyone?

You have to have clay to make cob, it's what holds the mix together.
It doesn't necessarily take alot of clay for cob, though it depends on
the particular type of clay in your soil.  I have heard of people
successfully making cob using clay somewhere in the range of 5% to 10% of
the mix.  The first thing I would do is just try making some cob test
bricks using the local soil mixed with straw or grass, let them dry and
test them to see how well they hold together, how strong they are, etc..
If you can't get it to hold together with the local soils available to
you, you only really have three choices:

   1) Find a way to extract whatever clay there is from the local soil
      (washing it out maybe?) so you can use it as a supplement to your
      cob mixes.
   2) Import some clay from somewhere else
   3) Use a building technique other than cob.

Shannon C. Dealy      |               DeaTech Research Inc.
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