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

[Shannon C. Dealy]

On Tue, 26 Oct 1999, Rosemary Lyndall Wemm wrote:

[snip]
> * The soil generally has a high clay content.  Sand may be the problem.
> It may have to be carted to the mountains from the sea.  [Possible]. 

While having a high content of coarse sand makes better cob, it is not
a necessity.  Other mixes will work, though they may require more
maintenance or better protection in wet climates.  I am currently putting
up a small building using the local soil without any additives.  The soil
composition is roughly 30-35% clay, 20% silt, and the remainder is either
fine grained sand or silt (measured by using a shake test, then allowing
the separated sample to completely dry).  I started the cob work just over
a year ago so I have seen the effects of wet winter weather on this mix,
which is minimal.  If you are in a hurry, or money is a problem, try just
using the local soil without any additional sand.

[snip]
> * Thatching is a known art in this region. It has the obvious problems
> of catching fire from the spirit stoves in general use.  Many people
> are burned to death from kitchen-caused house fires every year.  A way
> of fire-proofing thatch or a cheap alternative roofing system would be
[snip]

The primary reason that thatched buildings are such a fire hazard is that
the underside of the thatch is generally left exposed to the interior. 
When the thatch catches fire, it turns the entire building into a giant
chimney with the air from the interior feeding the flames.  I don't know
what style of thatching they are using, but for European style 
reed/wheat/rye thatching - (grass stalk thatch/not grass leaves), blocking
air flow to the underside of the thatch by completely covering the 
interior of the roof structure just below the thatch virtually eliminates
this hazard by slowing the burn rate to a virtual stand still.  One
approach described by Flemming Abrahamsson is to use wood scraps from a
lumber mill with cob to fill in the gaps.  An alternative cheaper approach
that might be workable in this situation would be to use a very thin
earthen plaster applied directly to the under side of the thatch, though
this will probably make it harder to do repairs on the roof.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
                      |    Embedded Systems, Real-time, Device Drivers
Phone: (800) 467-5820 | Networking, Scientific & Engineering Applications
   or: (541) 451-5177 |                  www.deatech.com