[Cob] RE: Coblist Digest, Vol 3, Issue 22To Chris Peters

[Bob & Lorraine]

Date: Sun, 6 Mar 2005 20:18:35 +1100
From: "Christopher Peters" <bollygum211 at dodo.com.au>
Subject: [Cob] Re: How to get a straight wall with cob
G'day Lorraine,......
Thanks Chris for your reply.
Our mix has been worked rather erratically depending on what time my
husband has had spare to help.
Several large farm-trailer loads each of a sandy gravel mix from one
part of the farm and several of wet, grey subsoil clay which sets like
rock at the first opportunity (and doesn't dissolve without a really
good soak for a number of days)were stirred together as best possible
with the backhoe, then the cultivator on the back of the tractor run
through it a number of times, water added  using a hose sprayed over the
mix, after that straw thrown in and again run through with the
cultivator.
I can see that we probably made LOTS of mistakes - there were lumps of
clay we had to either throw out or break up by hands and feet before
carting it to the wall, there was too high a percentage of clay, it
wasn't mixed and broken up well enough etc etc.  As time has gone on and
the tractor has gone through to pull the remainder of the heap together
and to break up the hardness that develops under the plastic cover each
night, the mix has become much more friable and workable.

Your comment about the red clay is interesting.  The clay where the
storeroom is being built is red clay and dissolves almost instantly when
water is added.  I'd tried clays from all around the farm until we were
thoroughly confused as to what we should be using, and rejected the red
clay as being weak.  Perhaps I should try adding a little of it to our
grey rock-like clay and see what results.

I'll take some photos within the next couple of days and see how I go at
putting them on the internet - we're not experienced in that either so
have to work out how to.

We are doing walls in two different ways:  
Husband wanted to use formwork to be sure the wall was straight (it
still isn't anyway) so one room is being built using the mix as rammed
earth.
The adjoining room is being done using cobs made from the mix.  We've
found we need a wetter mix to be able to press the mix into cobs, and
need to add a bit more straw. It's much slower as we are only going up
about 4 or 5 inches in height per course and can only add one course per
day as it wants to slump a bit too much otherwise.  We punch and pat the
cobs onto the wall, not walk on it - it doesn't seem to be suitable for
walking on without the fresh cobs being pushed off the wall.  Again,
this probably suggests our mix isn't right.

As I said, we're obviously making lots of mistakes.  It would have been
great to have been able to learn by helping an experienced person with
some building first, but we live on an island and it wasn't possible to
get to the mainland and find somewhere to learn.
Yes, we've borrowed a number of books on cobbing and earth building,
including Building a House in a Day. They've helped us, but seeing and
feeling a good mix, and helping do someone else's wall would have made
all the difference!

Thanks again Chris for your suggestions.  I'll keep you and the others
informed as to how the building progresses and the final results of our
mistakes (hope they won't be too disastrous!)

And thanks to you others out there who have taken an interest and
offered suggestions.  Much appreciated.

God bless you all,
Lorraine