Cob Clay, Fibers, & FC

[Mike Carter]

>how much fiber can we use to increase the insulation value without
>decreasing the strength of the cob mix.?

What kind of strength are you thinking of?  We found through engineering
compression tests that adding even a modest amount of straw drops the
compressive strength of our test blocks by an average of around 40%.  On the
other hand, the tensile strength should have increased by the addition of
the straw.  We have not been able to produce adobe-quality test blocks (300
p.s.i. or better) with any cob mix we have tried that includes a "normal"
amount of straw.


The low "R" values reported on this list for straw coated with clay slip
(whatever you want to call it) would indicate that increasing the straw
content is not an effective way to get more insulation.  We have been trying
to find straw "mini-bales" that we can attach to the cob on the outside for
that purpose.  So far, 10" thick is the smallest we have been able to find
bales.

If you have any info to the contrary, we would be happy to hear from you!

Mike Carter & Carol Cannon
cobcrew at sprynet.com
http://home.sprynet.com/sprynet/cobcrew
Austin, TX    USA