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

Shannon C. Dealy dealy at deatech.com
Mon Mar 21 15:03:20 CST 2005


On Thu, 17 Mar 2005, Bob & Lorraine wrote:

[snip]
> 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.
[snip]

Embrace the spluge :-) (or slump) I find it's a waste of time to try and
build the wall straight (I assume you mean vertically), if the fresh cob
sticks out 1/2 - 1 inch on each side, that's probably about right.
After the cob has had a little time to set (typically before you start the
next day's cobbing), trim the wall back to what it should be and throw the
trimmings into your next batch(es) of cob.  Different people use different
approaches to trimming, a machette works well (don't plan on using it for
anything other than cob trimming afterwards), though some people stand on
the wall and use a square bladed shovel to trim it by cutting downwards
from the top, and others use old saw blades.  You will also get faster
drying and a better surface for plastering this way, as hand worked cob
tends to have a smooth suface which kind of seals the wall, trapping
moisture and doesn't give as good a bonding surface for the plaster.


Shannon C. Dealy      |               DeaTech Research Inc.
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