Cob Re: Plastering

[Eric Hart]

At 09:18 AM 12/20/97 +0000, Pat wrote:
>There was a bit of a discussion going on in the strawbale list about 
>earth plasters. Since I've started plastering NOW. I thought I check 
>if this subject has any interest in the cob world.
>On the outside of my house I am  using earth plaster for those areas 
>that have protection from the rain and stabilized earth plaster (20 % 
>cement) for those areas that do not have protection from the rain. 
>Inside I going with earth plaster. 
>
>I've wondered about linseed oil since it's used for  earthen floors
>but for some reason I've never heard of it being used for walls? Not
>sure why. Also the the linseed oil and wax mixture (also used for
>floors) sounded interesting.
        I used some linseed oil in a clay based plaster on the strawbale
educational display I used to have.  It helps a lot to stabilize the clay
plaster so it isn't so friable.  Robert LaPorte in his book Moose prints
suggests about 1% by volume of linseed oil in your natural plaster.  It
doesn't take much and its sort of a guessing game how much is enough.   I
did a base coat of clay (in this case a processed Hawthorne Fire Clay from a
pottery supply store) with sand only and then added linseed oil for the
final coat.  The end result was smooth and I couldn't get any clay on my
finger  (or the floor) when I ran it across the wall.  I did have some
problems with cracking which I fixed by wetting the cracks and rubbing the
crack with my finger to fill in the crack.  I didn't do any 'crash tests' of
the wall but imagine it would be durable for most applications.  I would
want to do more durability tests before putting in my house.  Clay dust is
not something you would want to have in your house.  Its very fine and is
hard to clean up.  Those fine particles get stuck in your lungs and never
get out.  Clay also stains which I guess you have figured out.  So, there
are some suggestions from my limited experience.

Eric D. Hart
Community Eco-design Network
PO Box 6241
Minneapolis, Minnesota  55406  USA
(612) 306-2326
http://www.cedn.org