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onlinehandyman 01-05-2009 08:20 PM

Bathroom Ceiling Peeling
 
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Recently a friend of mine noticed that their bathroom ceiling was peeling ( I have attached pictures ). All that I can tell is that it is old and a semigloss. I am trying to figure out why the ceiling is failing. I realize that it is old and in a bathroom with a shower, but before I repair it I am trying to decide on my best plan of action. I am also thinking that it maybe latex paint over oil based paint or primer. I would very much appreciate any ideas as to what type of paint and primers to use and any other necessary steps to repair this thing as best as possible. I have already peeled the loose paint and filled the spots with joint compound.

Nestor_Kelebay 01-05-2009 11:59 PM

Quote:

I have already peeled the loose paint and filled the spots with joint compound.
Good. Now, just sand the joint compound patches smooth, prime the bare plaster areas with EITHER a latex or alkyd primer and repaint the whole ceiling with a paint made for humid conditions like Zinsser's PermaWhite Bathroom Paint, available at most home centers.

The problem is not that the pre-painting prep work wasn't done well or properly. The problem is that it was an inexpensive "PVA" paint that was used to paint that bathroom.

In North America, almost all the latex paints are made from one of two different kinds of plastic; polyvinyl acetate or polymethyl methacrylate.

PVA stands for "polyvinyl acetate" which you probably know better as white wood glue. White wood glue is a good adhesive, but it both softens up and looses it's adhesion in wet or humid conditions, exactly like you have in a bathroom. Unfortunately, that's a trait that seems to be impossible to engineer out of the PVA molecule. So, every PVA paint is subject to softening, cracking and peeling (or otherwise failing) in humid or wet conditions, just like you find in bathrooms.

Although this problem is primarily confined to the bathoom ceiling above the bathtub, you can also find paint peeling high up on walls where they meet the ceiling. This is because the air in that corner can loose theat through the wall and ceiling simulataneously, so those corners are cooler than the rest of the room and there's more condensation on the paint near where walls meet ceilings.

Better quality paints will use a different kind of plastic as the binder resin. They will use a plastic called "polymethyl methacrylate", which you probably know better as "Plexiglas". Plexiglas is much more resistant to moisture and humidity then PVA is, and doesn't loose it's strength and adhesion in a moist and humid environment the way PVA primers and paints do.

So, almost certainly, the problem here was caused by using a cheap house paint in a humid bathroom. The problem can be solved by simply patching the bare plaster or drywall areas with more joint compound, sanding smooth and painting over those patches with a paint made for use in bathrooms like Zinsser PermaWhite. Paints made for bathrooms will also have mildewcides added to them that will prevent mildew from growing on the paint. That keeps the bathroom looking good.

And, two coats of Bathroom Paint will remain mildew free (and isolate the underlying PVA paint from moisture and humidity) much longer and better than one coat.

sirwired 01-06-2009 03:31 PM

You should also scrub (and rinse) the paint with a strong cleaner. This will remove things like hairspray residue that are murder for paint adhesion. In addition, try not to take a shower in the bathroom a week before and after the priming and painting.

Does this bathroom have ventilation? If not, this would be an excellent time to install it.

Lastly, I would put a high-quality bonding primer up before painting with bathroom paint. Since you already have known adhesion issues, it would be a good idea. (I use SW PrepRite ProBlock Latex. Avoid any water-base Kilz product.)

SirWired


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