Cob: Paint on cob

[Brian Gregor]

On Thu, 6 Mar 2003, Darel Henman wrote:

> Kim,
>   don't put paint on cob.  Too many people think a cob wall will
> disintergrate at the first rain and this is untrue.  I have seen hundred
> year old daub buildings with NO lime plaster, just the rough daub still
> in pretty good condition.

Here's a probably-impossible-to-answer question: what effect does
geographic variation in clay composition have on the longevity of cob when
it's exposed to the weather?

Leaving aside weather variations, I imagine there's a huge difference
depending on the particulars of the clay, sand, and straw proportions,
the size and shape of the sand, and the clay composition.  I'm no
geologist, but surely the clay in England is different from, say,
the Boston blue marine clay common here in Mass.  (incidentally,
the Big Dig is giving away another 1 million cubic yards of clay,
if any northeast cobbers are short :) )

I'd say to play it safe and protect the cob with
tried-and-true weather-resistant finishes like lime/sand plus
overhangs, unless your tests have shown otherwise.  Paulina
Wojciechowska's book "Building with Earth" contains several recipes for
further waterproofing lime mixtures.


-brian