flaking paint on plaster

[julianas]

Problem #1) My house was built in 1912 and has plaster on lathe walls (interior walls) and plaster on concrete/brick walls (exterior walls). When we started prepping the living room for painting we discovered that in large areas, the paint comes off in large flakes (1-2 inches wide/long) with minimal effort using a scrapper. There are several (4-5?) layers of paint in the flakes and it comes off all the way down to the plaster. In some areas it looks like they left old wallpaper glue on the plaster, but in other areas where this is happening it is just the original plaster. And the flaking doesn't happen everywhere either. Some large areas (10-15 square feet) the paint just comes off in chunks/flakes, and in other large areas the paint won't budge. There doesn't appear to be any water damage to the plaster, although the paint does flake more near small cracks in the plaster and near windows and doors. So, here are questions...

1) Any idea why this is happening? I think the old wallpaper glue is one problem, but it's happening in large areas without any glue as well.

2) Do we really have to remove all the old paint that's flaking off? It's not literally falling off the plaster, but it does come off with scraping. (It's happening on the ceiling too, so I don't relish doing all the scrapping over my head.)

3) Since there are areas where the paint comes off and areas where it won't despite a lot of effort, the walls are rather uneven looking. Plus there are areas where the plaster isn't in the best shape and has a lot of chips in it. I was thinking of skim coating joint compound over the whole wall to cover up the texture from the paint that won't come off, fill in the cracks/chips and hide the differences between different areas of the walls. Does this make sense?

4) What do we need to do to prevent it from happening again? What I was planning on doing was, after the skim coat of joint compound, priming the walls at least twice with a PVA primer and then painting. In the areas where the paint won't come off, I was going to clean with TSP before skim coating. Should I be doing anything different?

Problem #2) Ceiling in the same room. Not only is the paint chipping/flaking down to the plaster in areas, but the top layer of paint is just peeling off in areas as well. I was cleaning off wallpaper glue from the walls with hot water and tried spraying one of the peeling areas on the ceiling with water just to see what would happen. After the water sat there for about 1-2 minutes, the paint just scrapped right off in sheets. The layer of paint right underneath it seemed fine. It looks like someone put up some spackle or other substance on the ceiling (who knows why), but never primed it, so the paint isn’t adhering to it well. The question here is: I know I need to scrape the areas that are actively peeling, but should I do it for the whole ceiling? And how thorough do I need to be about getting that top layer of paint off? Is it okay if some of that layer is left behind and I just prime over it? Or will it probably peel at some point in the future?

Any suggestions/ideas/thoughts would be much appreciated!!!

Thank you!
-Juliana

 

[Nestor_Kelebay]

Julianna:

I have the same situation in my building where I can easily scrape the paint off to the bare plaster, and it's not the problem you think it is. The paint is adhering to the plaster, but the 5 or 6 layers of paint you have on it are mostly oil based paints that dry to a hard, stiff film, and what's happening it that it takes more force to break that paint film than it does to pull it loose from the old plaster. Consequently, once you start peeling that paint off, it's not hard at all to peel large sections of the paint off.

Do this: Use a snap blade razor knife or any sharp tool to score around any paint that you want to remove, and then pry the paint off UP TO that score line. That paint has been sticking to your walls for 90 years, and unless you intentionally peel it off, it'll stick for another 90.

Just apply joint compound with a 4 inch taping knife to the plaster near where you scored the paint to eliminate any "step" in the painted wall between where the old paint was left on the wall and where it was removed.

Where you have a top coat of paint that's peeling, then you should scrape the paint down. The problem is often that not all latex paints are equally resistant to moisture, and some will loose their adhesion if they get damp and stay damp for a while. This could very possibly be why that top coat is peeling. However, if you then paint over that low quality paint with another coat, then it doesn't get as damp (because it's covered by another coat of paint) and can stay stick to the wall or ceiling well. That is, the reason why it came off very easily for you when you got it wet is because PVA based binders loose their adhesion when they get wet. If you paint over that PVA paint with a 100% acrylic paint, then the PVA won't be exposed to as much humidity and perhaps condensation, and so adhesion of the PVA will probably not be a problem once it's covered by another coat of paint to keep it dryer.

I've bought some lumber to make some shelves in tenant's lockers. Digest what I've said and do your own experimentation if you want to to check that I've diagnosed the problem correctly. If you have more questions, I should have more time tonight to post again.

 

[julianas]

Nestor,

What you're saying sounds right and makes a lot of sense for both the walls and ceilings, so I'll follow your advice on that for sure! (It ends up saving me a lot of time and effort.)

Of course, if the ceiling continues to peel after we paint it, I'll come haunt you! Teasing of course.

Thank you!!

-Juliana

 

[Nestor_Kelebay]

No, Julianna, it's common for PVA paints to lose a lot of their adhesion when they're damp. People generally don't know that because most walls stay dry. If the paint only scrapes off easily when it's damp, then covering it with a better quality moisture resistant paint will keep the lesser quality stuff under it dry.

Lot's of people think that there's no real difference between cheap paint and expensive paint, and that's just not true. You can't go wrong buying top quality paint.