How to make cob

[Shannon Dealy]

On Thu, 19 Sep 1996, Aodhan Mac Domhnaill wrote:

> Hello There folks,
> 
>                    I've been fascinated with alternative building styles and
> COB seems to right for me. Unfortunately I know very little about it.
>                    At the moment I live in Australia but will be going back
> to live in Ireland next year and would love to build my own home. I would be
> very grateful to anyone who could steer me in the right path. Questions
> like, how do you know if you have the right sort of clay ? What are the
> proper mixtures? How much straw do you put in with relation to the other
> ingredients? 
> 
As I understand it, most any clay will work (my experience is limited in
this area).  Straw ends up being about 10% of the volume of the cob, but
it is not explicitly measured when making the cob, it is simply added to
the mix until it reaches the right consistency.

I was trying to address the specifics of making cob in my posting of 
earlier this week, from the above, I assume that my posting either was 
not received by everyone, or it fell short of the mark.  Possibly it
is simply the fact that I gave ranges for the amounts of sand & clay.
If this is the case, perhaps I can clarify.  Cob is a very forgiving 
material, and does not require a precise mixture to get a good wall.  The 
ranges tell you if your soil is adequate for building cob by just adding 
straw, or if you need to supplement your soil with sand or clay.  If it is 
necessary to supplement the soil, you only need to add enough sand or 
clay to bring the soil mix to within the specified ranges.  It should be 
noted however that the ranges are a starting point, soil compositions 
differ, and there is no  substitute for making up small mixes and 
creating a few cob test bricks to check for strength and the best mixture.

I am going to try to cover the specifics of building with cob in detail over
the next few weeks, and I hope all of you will let me know if anything is
unclear (or if I am boring you) :-).  For those of you who already know 
how to make cob, jump in anytime.  I am assuming that this is the kind of
information most of you joined this list for.

NOTE: There will be a bit of a delay before the next installment, I have
to perform some system upgrades (which hopefully will not disrupt the
mail system).


Shannon Dealy
dealy at deatech.com