PVA Disaster

bobcatmAugust 17, 2010

PVA Primer Disaster

We took the advice of the local paint store and applied PVA Primer over new veneer plaster and skim-coated old plaster being done as part of a bathroom remodel.

The paint has severe adhesion problems, and with doing just a little research seem that it is due to the use of PVA primer. From what I subsequently read (should have done my homework up front) PVA should not be applied to alkaline surfaces (lime containing) such as the veneer plaster. I believe that the cause of the bad advice was that many people equate plaster to drywall even when we’ve stated plaster, not drywall.

“Polyvinyl acetate (PVA) primers should never be used over a plaster finish as it will cause bond loss and paint delamination”

The PVA and Acrylic Satin enamel finish coat were applied approx 3 months ago. The plaster was done approx 1 month prior to that, a thin veneer coat (diamond) on the new work and skim coat over old sound plaster. The surface of the plaster was properly prepped (vacuumed and wiped down). The bathroom is fairly well vented with a good fan, certainly moisture in the air, however have never see droplets on the walls or ceiling or had any mildew problems.

Questions:

1) I’ve removed approx 80% of the finish coat and PVA primer on the walls (peeled off together). In many areas I could tear off big 1’x1’ pieces of paint with my hands. Other areas I used a single edge razor to “zip” the paint off. The remaining 20% is adhered better but not sure if adhered well enough to leave. I can remove it with a lot of elbow grease and the razor but is now very slow and am risking gouging the plaster. I’ve tried the heat gun but that doesn’t seem to help. Am concerned that chemical stripper will leave a residue and cause further adhesion problems or cause delamination of the veneer plaster or skim coat.

Any recommendations on removing the remaining 20%?

2) When we first noticed adhesion problems, we thought it was a just few patches where the surface was somehow got missed and were dusty (turned out not to be the case). So we have a few places where we spot primed with new PVA that doesn’t scrape off. (The “old” PVA likely failed partially due to the moisture from the latex top coat.)

Any recommendations on removing the remaining fairly small areas of “new PVA”. ?

3) The removal has resulted in some small scratches/gouges in the plaster.

Any recommendations of how to best address these? I really don’t want to skim coat the whole room again as the trim is already installed etc.

4) We have considered several options for the 2nd go-round of primer and finish coat. Have done a quick look for Alkali resistant primers and found a few masonry primers (have only found acrylic ones, no oil). Based on being old-school and the catastrophic failure of the PVA would prefer oil, but so far have not found any oil primers specifically stating that they are alkali resistant (veneer plaster has a ph of 12). Also as far as finish coat, am concerned about a similar reaction of the water from the finish coat causing the primer to lose adhesion.

Any recommendation for primer and finish coat? (Brand names and product #’s are a big help)

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