Cob: plastering adobes

[John Fordice]

Experience has shown the use of portland cement plaster (commonly known
as stucco) to be detrimental to earth walls.
As I understand it, what happens is:  The stucco will develop cracks (
as stucco does ) & this will let water into the wall.  Since the stucco
passes water vapor more slowly that the earth wall, the moisture will
tend to collect in the outer portion of the earth wall.  When the wall
cools at night or in cold weather, the moisture that has thus been thus
essentially trapped in the wall will then condense on the backside
(earth wall contact side) of the stucco and cause a softening of the
earth wall it that point.  This ultimately results in a spalling off of
the outer layer of the earth wall and a loss of bond between the wall at
the stucco covering.  The stucco then is free to crack even more,
aggravating the condition & it eventually comes loose and takes a
portion of the outer surface of the wall with it.
So the stucco which was put on the wall to protect it, actually damages
the wall & makes for greater erosion of the wall than if it had been
left un plastered.

If you wish to plaster cob, use an earth or lime sand plaster.   

ben graham wrote:
> 
> Laura,
> 
> I think you have the right idea.  Plastering adobe is just like
> plastering cob.  All the in between brick spaces actually support the
> plaster better, so no lath is necessary.
> 
> Best
> 
> Ben Graham
> 
> >From: "Laura Guldin"
> >Reply-To: "Laura Guldin"
> >To: coblist at deatech.com
> >Subject: Cob: plastering adobes
> >Date: Thu, 01 Mar 2001 22:31:54
> >
> >Hello yaall,
> >I am in Texas visiting my friend who's building an adobe. She's
> >cement
> >stuccoing the outside (not my idea) and I am talking to her about
> >earth
> >plastering the inside. The adobes are cement stuccoed together.
> >Anything
> >special about adobes.? She put lathing on the outside adobes. I
> >don't want
> >to do that.
> >Any ideas or hints? Is it pretty much like plastering cob?
> >Thank you kindly
> >Ulani
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