cob in patio wall

[Shannon Dealy]

On Wed, 4 Sep 1996, Janet Moore wrote:

> [SNIP] 
> Thanks, Shannon, for the insights. The type of wall I was thinking of would
> be unroofed; not a wall for a structure but an outdoor wall maybe 6 feet
> high, in lieu of a fence, the kind of thing you might use to enclose a
> courtyard.
> 
> What alternatives are available for a foundation for a wall like this? Would
> it require the same foundation as a house wall (lots of concrete)? Is there
> a formula for a weather-resistant plaster? I live in a fairly dry climate
> (Southern Colorado), but we occasionally get fierce thunderstorms.

I remember seeing some pictures of a cob wall used as a fence, the wall 
was built using a simple dry stone foundation (no mortar), and topped with
tiles to protect where most of the weathering will occur (see below).
Because of the mass of these walls, you should build them in a curve or
'S' shape to give better stability, particularly since outdoor walls tend
to extend for some distance without any supports.  The best way to make
sure a wall doesn't fall over is to design it so it can't.  Curving the 
walls adequately ensures this.

With regard to house foundations, Cob Cottage Company uses stone 
with a lime-sand mortar, so concrete is not necessary (though building
codes may say otherwise).  As for weather resistant plasters, I don't 
have a formula, though I imagine a any good book on plasters would list
some, you might look under stucco.  Another possibility is to just build
the wall and let it stand for a year and then decide if you want to plaster
it after seeing how well it holds up to the weather.  I believe the picture 
of the tile capped wall that I saw was unplastered.

     /\
    /  \   tile (one tile each side)
   /|  |\
    |  |
    |  |   cob
    |  |
    |  |
   ======  stone foundation
   ======
---------- ground

Shannon Dealy
dealy at deatech.com