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GSBN:Plaster on Framed Walls

 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?

I've never made a study of it, but in the many plaster walls I've torn open,
I always assumed that, to some degree or other, the plaster sheet was just
hanging there on the lath, and, when tapping on a wall with a hammer, I've
always heard plenty of things that sounded like hollow spots....

John "Hola-Hollow" Swearingen

On 10/8/07, Jeff Ruppert jeff@... wrote:
> Bill,
> 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.
> Jeff


John Swearingen
Skillful Means, Inc.
Design and Construction

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