Cob: straw clay insulation questions

[Shannon C. Dealy]

On Thu, 20 Jul 2000, Marlin Nissen wrote:

[snip]
> My first experience with clay/straw has been somewhat disasterous, no
> drying, slow production etc. and I feel like I must be missing something.
> 
> Can any of you out there that have put up straw/clay (not high mass Cob)
> in between trusses PLEASE respond ?  We may try cordwood with earthen
[snip]

You should expect it to be slow drying once it is in place as there will
be little or no air circulation through it.  It should help considerably
if you let it dry outside until it is just barely damp before putting it
up.

There are two approaches to straw-clay that I have dealt with, both start
out the same way.  You take clay-slip (clay mixed with water to get a kind
of split-pea soup or somewhat thinner consistency), pour it over a pile
of loose straw, and stir it around until each fiber of the straw has a
very light coating of the clay slip.  Mixing it seems to be easier if the
pile is on a couple old pieces of plywood or other hard surface and you
use a pitch fork to toss it and turn it repeatedly.  Next allow the mix to
dry until it is just barely tacky (spreading it out and turning it a few
times will help it to dry faster).

At this point if you are trying to make straw-clay panels, you pack the
mix into a form and ram it tight using a piece of wood or other implement.
If you have done this right, you can remove the panel from the form
immediately and it should hold together.

If rather than panels, you are just trying to fill a wall or ceiling with 
insulation, you just pack the mixture into the wall or ceiling.

It does take a little practice with this technique to get the right
consistency of coating on all the straw fibers.  To much clay, and it
reduces the insulation value, significantly increases the drying time, and
makes the final panels or insulation mixture much heavier.  Of course if
you apply to little clay, the mix will not hold together when dry, and
may not be sufficiently coated to provide adequate fire protection.


Shannon C. Dealy      |               DeaTech Research Inc.
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