[Cob] Plaster failure question

[Patrick Newberry]

Not sure exactly but I've found that if I first paint the cob wall with
a lime wash first and let it dry (does not take too long, a few hours,
then plaster it's not only easier to plaster, seem to stick better too. 

I just take plain old hydrated lime, mix it with water in a 5 gal.
bucket till it good and white but still paint / white wash like and
paint it right on the cob wall. Rather than plaster I have been putting
3 coats of this on the wall it it is very nice and white. It's thin
however and if you bump into it while doing things like moving furniture
in and out and such it will show the under laying cob which in my case
is redish. But it's pretty simple to mix up some more lime and just
repaint it. 

Pat Newberry
www.gypsyfarm.com



"Computers are useless. They can only give you answers." -- Pablo
Picasso 


-----Original Message-----
From: coblist-bounces at deatech.com [mailto:coblist-bounces at deatech.com]
On Behalf Of Georgie Donais
Sent: Tuesday, May 16, 2006 9:23 PM
To: coblist at deatech.com
Subject: [Cob] Plaster failure question


I plastered a cob wall last fall with lime. It was type S, so sometimes
was 
soaked overnight, often less than that. I followed all the instructions
(I 
think) in Cedar Rose's plaster book for mixing and applying, and added a

small amount of pozzolanic additive to speed up the curing process a bit

(Marlin brought me up to speed on that). I had trouble keeping the wall 
covered and moist for a week, with all the curious onlookers who kept 
pulling off the tarps to look.

The plaster hardened nicely, and seemed to be in good shape going into
the 
cold season.

Over the winter and spring, it became obvious that significant portions
of 
the plaster had pulled away from the wall and was primed to fall off, or
be 
knocked off by passersby. I can go around the wall and, by knocking,
tell 
by the hollow sound that some plaster didn't adhere/pulled away.

So we'll be removing everything hollow and redoing those parts. My
question 
is, when plaster fails like this, is there a common culprit? Mix, 
application, treatment afterward, wall preparation? My notes don't give
me 
clues as to why some parts would fail and some would not. Some
elucidation 
would be appreciated. Thanks for your help!

Georgie
www.cobinthepark.ca



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