Originally Posted by mspdet
Hi I am having a problem trying to fix my bathroom ceiling, it's plaster and I have used latex primer & paint and oil based primer & paint, both have cracked and peeled. How can I fix this problem from never happening again
There is the very high liklihood that the problem is the KIND of paint you're using.
You see, inexpensive latex paints are made from a plastic called PVA (for polyvinyl acetate), and which is also what white wood glue is made of. As a result, the properties of white wood glue and inexpensive latex paints are somewhat similar. Inexpensive PVA paints will dry slightly sticky (a characteristic known as "blocking") because adhesion is something that's hard to engineer out of the PVA molecule. White wood glue will re-emulsify if it gets wet, and that's true even if it's been dry for years. (That's how furniture repair shops take apart furniture that's been glued together with white wood glue.) Similarily, PVA latex paints will soften up and lose their adhesion to the substrate in moist and humid conditions. And when that happens, the PVA paint will crack and peel off the substrate.
Look on your bathroom walls and ceiling to see where the paint is cracking and peeling. Generally, if the problem is that you're using PVA paint, it'll be worst on the bathroom ceiling right over the bathtub (cuz that's where people shower), and at the corners where walls meet ceilings (cuz that's the coolest part of the bathroom cuz heat can be lost through the wall and ceiling simultaneously resulting in more condensation forming on the wall and ceiling in those areas.
MOST of the time when people have paint cracking and peeling in bathrooms, the problem is that they're using a paint not meant for high humdity conditions. And, most of the time the cause of the problem is misdiagnosed as poor preparation work on the walls and ceiling prior to painting. And, of course, this can be frustrating to the homeowner who KNOWS he did a top notch job of preparing the walls and ceilings prior to painting.
The real problem is that the subject of paint isn't being taught anywhere, and the result is that most people don't know enough about paint to diagnose paint problems. It's like trying to figure out what's wrong with a washing machine if you don't know how it works.
What you need to do is scrape off the peeling paint, skim coat the area smooth, prime with whatever kind of primer you like and then repaint with a paint meant for bathrooms like Zinsser's PermaWhite Bathroom paint (or any paint meant specifically for bathrooms). Such a paint will:
1. Have mildewcides in it that kill mildew spores that land on the paint before they grow, keeping your bathroom walls and ceiling free of mildew, and
2. Be made from a plastic called "polymethyl methacrylate" (or PMMA) which you probably know better as Plexiglas. PMMA plastic is much more moisture resistant than PVA plastic. There are many different PVA and PMMA resins used to make paints, so anyone making a paint to be used in bathrooms will choose the PMMA resin that has the highest resistance to moisture. That means that it won't soften or lose it's adhesion to the substrate when it gets wet, or change it's properties in any other way under moist or humid conditions.
This is why it's important to use a paint specifically made for bathrooms rather than just use any high quality latex paint. Those made for bathrooms will have the mildewcide in them and will be the most resistant to humid and moist conditions. High quality latex paints made for general purpose use will have harder resins in them that dry to harder films so that the paint doesn't scuff up as easily and marks can be cleaned off without lowering the gloss of the paint. Those things are important, but they're more important in a kitchen, living room or bedroom. In a bathroom, you need resistance to moisture and humidity more than you need hardness.