Cob Re: mud from tidal flats

[Shannon C. Dealy]

On Sun, 15 Mar 1998 bufflocp at telusplanet.net wrote:

[SNIP]
>    In the area where we'd like to build, I've not noticed much mud other
> than that located in the tidal flats, exposed at low tide. Would that kind
> of mud be likely to be suitable for cob?
>                                                                 Ron

I'll give the easy answer, it depends :-)  I have seen a few tidal flats
which might be suitable (at the mouth of a river or stream which would
continually wash down new material), but I would expect in most cases,
the clay content would have been washed out, and the sand content would 
have had the sharp edges worn off which would make it a poor choice.

Ideally what you are looking for is a soil containing a mix of sand and
clay, with the clay content generally being between 10 and 30 percent
(depending on the characteristics of your particular clay), and the
remainder being sharp sand (as opposed to rounded beach sand).  Given
the ideal, cob will let you get away with quite a bit, it will tolerate a
fair bit of silt, excessive clay, and a variety of other variations.

There is some good discussion of cob mixes and the basics of how to make
cob in the earliest coblist archives, I would suggest you take a look at
the August through December 1996 archives.  The "howto cobstruction"
thread may be of particular interest:

    http://www.deatech.com/natural/coblist


Shannon Dealy
dealy at deatech.com