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Re: GSBN:Re: Lime plaster problems


I have to agree with everything you have said.  In particular, we had
the experience of delamination of the lime color coat from repair
patches in the earth base coats.  Since then, I have cautioned clients
in applying lime over earth for some of the very reasons you have described.

To explain, we had applied earth plaster base coats, which included a
small amount of lime, over plywood sheathing covered with building paper
and mesh.  There were some spots on one wall that were not applied
against the wall well enough, leaving a hollow space behind the base
coats (this was the final wall on the project and was done in the
dark).  After drying, the contractor went around poking holes in the
wall where this was the case (I am not totally convinced every spot he
poked was going to be an issue, but that is for another discussion).  We
proceeded to patch those areas with fresh earth plaster and let it dry
for a few days.  Everything appeared to dry out after a short period,
but what had actually happened is that the plaster had froze, holding
the moisture in (we were working in October with cold nights and this
was a north facing wall).  We then put the lime color coat on the entire
building.  Some warmer weather arrived shortly thereafter as it can here
in the mountains (Indian summer...).

After a week or two, on that one wall where we had patched, the color
coat was left hanging and could be scraped off with no effort on every
patched spot.  What you described as the earth base coats shrinking
during drying makes sense.  I have to admit that it took me awhile to
figure this all out myself and you confirmed my thoughts.  We have used
lime in freezing conditions with very successful results given the harsh
conditions, so to me it was an issue with the bond and the differences
in movement between the materials.

It was a good lesson to learn, and one that brought up another question
that has been in the back of my mind since.  How many small air pockets
end up behind plaster applied to framed buildings with building paper
and mesh on an average job?  I can't believe that /every /successful
plaster job on framed walls out there is 100% sucked to the wall.
Granted this wall was done in the dark and it was ultimately our
responsibility.  It was sprayed on as we have done many other times.
But no one has ever gone back to poke at the walls in the way this
contractor did, creating areas for us to patch.  It seems suction from
the trowel could easily, and unknowingly, pull the plaster away from the
wall in small spots no matter who is doing the work.  I have never
witnessed plaster failure due to this, so I cannot speak to it as a
failure mechanism.  If a contractor were to ever do that again I may
have a different response based on the experience explained above, and
was wondering if anyone else has had such an experience?

If anyone responds to this second topic specifically, maybe a new topic
is in order so as not to combine the two.