Cob Clay, Fibers, & FC

[Will Firstbrook WCB of BC]

Hi Ron,

The best way of finding out what clay works best in your situation is to make test bricks of varying proportions of clay sand & earth that are available at your site. For each brick, record its recipe and when dry compare its properties, such as strength, weight, cracking, does it crumble, easy to break or is it rock hard. Some clays have quite high silt content making them less suitable. Stickiness is a good indicator as the clay is basically used as a glue.

Fiber cement would probably work ok for non-load bearing interior walls. But you might also want to consider other alternatives such as clay straw which is also cheep and doesn't need custom mixing machines, or thin burlap bags filled with stabilized earth and wood chips, or other combinations. You could also use other natural recipes such as roman cement which has held up the Roman aqueducts for the past 2000 years. I have forgotten its recipe but it is light and strong. I would look towards using available natural materials that are close at hand (on your property) for the best return.

What is pine straw? Is it the smooth pine needles you are referring too?

Regards,
Will



 -----Original Message-----
From:	coblist [SMTP:coblist at deatech.com]
Sent:	Thursday, October 15, 1998 8:49 AM
To:	coblist; WFIRSTBR
Subject:	Cob Clay, Fibers, & FC

Greetings All,

So, for my first question/contribution to the list, I have a concern about
clay.  In this area, we have two types of clay:  an orangey-reddish clay that
is most often found in the upper levels of soil, and a sticky grey clay (it's
called gumbo around here) that is often found a bit deeper.  While I suspect
clay is clay, instinct tells me that the gumbo would be a better choice to use
for cob.  From the broad range of experience out there, I'm wondering if you
all feel there is any benefit to using one or the other?

Second, I'm curious about what plant fibers work well in cob.  I've read the
archives (yes, ALL of them!) and while I've read of folks using plant material
other than straw, I'm curious if anyone has tried pine straw?  With all the
pines in South Carolina, we have an abundance of the stuff.

Finally, regarding fibrous cement: if I understand correctly, one of the main
drawbacks to the material is water absorbency, making it unsuitable for
exterior walls and such in wetter climates.  However, what about using it for
lightweight, non-structural interior walls?

Metta to all,

Ron Cameron