Cob retaining wall

[Shannon C. Dealy]

On Sat, 9 Nov 1996, Eric D. Hart wrote:

> Hello everyone:
>         Just thinking of what cob can be used for short of building a house
> or shed.  I'm involved with a community garden initiative in Minneapolis and
> we may have to put in raised beds on some of the lots we can garden.  If we
> end up constructing the raised beds, the 'standard' way to create them is to
> used treated lumber.  This kind of lumber is expensive and uses toxic
> materials to make it rot proof so I would like to avoid using it.  Could we
> build a small cob wall that is a small retaining wall to form the raised
> bed?  I don't know how the cob would hold up to the water and roots but it
> might work.  Maybe if you put a small edge of gravel between the wall and
> the soil that would help.  If the cob would work, it would be a community
> building project to construct the walls rather than just having someone with
> a power saw construct the walls.  
> 

It might work, I was thinking of trying something similar inside a
greenhouse where moisture levels can be better controlled.  I think you
would just have to try it to find out.  It would help to put gravel
between the wall and soil (as well as under the wall) as you suggest to
provide a moisture break. In addition, it would probably be a good idea to
make the walls in a buttress shape in order to help it hold together when
it's wet.  Cross section of walls:
   _        _
  / |______| \
 /  | soil |  \
/___|______|___\

To further enhance the life of the walls, it would be a good idea to cap
the walls to reduce direct contact with rain, a simple approach would be
to cover the top with a series of large flat rocks.


Shannon Dealy
dealy at deatech.com