While prepping my walls with TSP - paint bubbled!
I am just prepping my walls with TSP and hot water now and in some areas of my wall, the paint is starting to bubble. Looking closely there is a bit of flashing in those spots which means that the coat underneath what I am about to paint over may have had some grease or even oil paint there.
Can I save myself from sanding the entire wall by just sanding the areas with bubbling?
I am about to use Farrow and Ball which is a very pricey paint and I don't want to have to re-do the job or have it turn out with bubbles so I'd rather get it right the first time.
Any suggestions... or do I need to sand the whole wall?
Latex paints in North America are made from one of two different kinds of plastics; polyvinyl acetate (which you probably know better as white wood glue) and polymethyl methacrylate (which you probably know better as Plexiglas).
Polyvinyl acetate paints will loose their strength and adhesion when they get wet, and I expect the bubbling you are experiencing is due to the fact that you're using TSP to prep a wall painted with polyvinyl acetate paint.
The result is that the paint is loosing it's adhesion and coming loose from the wall.
TSP was used to clean walls back in the 1950's and early 1960's because it had the unique advantage of dulling the gloss of OIL BASED paints. Back then, even interior paints were all oil based paints, so by cleaning a wall with TSP prior to painting, you dulled the gloss of the oil based paint, thereby making a matte surface that any subsequent coat of paint would stick well to.
When ICI Ltd.'s "Glidden" line of paints introduced the very first interior latex paint in 1959, people weren't aware that TSP only dulled the gloss of oil based paints. It didn't dull the gloss of latex paints. But, because people weren't aware that TSP only worked on oil based paints, they kept using TSP to clean walls painted with latex paint prior to repainting. TSP doesn't dull the gloss of latex paints at all. So, if you are cleaning a latex paint in preparation for painting over it, you'd be better off using a better cleaner like Mr. Clean or Fantastic to clean the old wall prior to repainting. At least then you'd be using a better cleaner than TSP.
What I would do is scrape the loose polyvinyl acetate paint with a paint scraper to remove any loose paint, skim coat over that area with drywall joint compound, allow to dry and sand smooth. Then put a coat of primer over the area, allow to dry, and paint with a good quality paint.
If it's a latex paint you're cleaning, then use a good cleaner like Mr. Clean or Fantastic. TSP does not dull the gloss of latex paints, so there's no advantage in using it on a latex paint prior to repainting.
You won't really know untill you get into it if that means all the walls or not
If a simple cleaning solution bubbles the paint off the wall, then it is not properly adhering, and the water from a fresh coat of latex could easily pull the previous coat off also
Perhaps it was due to contamination, and is only in one area
If you do find other areas/walls that hold up to scrape/sand, that would be considered firmly adhering
I'd still strongly suggest a full coat of problem solving penetrating primer (such as Zinsser's Gardz) over the whole thing before applying the F&B
I'm thinking another cause for the bubbling may be that the joint compound under that paint was thinned so much with water when it was applied that it dried with very little strength.
If water penetrated through the paint and began to evaporate into a vapour, the pressure could have caused the joint compound to crack, allowing a bubble to form in the paint.
That is, the separation didn't occur at the paint/joint compound interface, it occured within the joint compound near the paint, where that joint compound was very weak.
I've had this happen myself. I used to use a spray bottle to wet the surface of joint compound so I could spread it smoother once it was already on the wall. You can spread it smoother, but the addition of the water right at the surface means that the joint compound right at the surface is much weaker than the stuff deeper down. I no longer mist joint compound to spread it smoother BECAUSE I've had problems with blisters forming in those areas; either after priming or when cleaning the walls. What exactly causes the blisters, I dunno, but I'm thinking it's the water penetrating into the joint compound and evaporating to create pressure.
thanks for the tips - I was not aware of the fact that TSP wasn't useful on latex paints... even after having worked in a paint store for 3 years - albeit more than 10 years ago.
The water was lukewarm, maybe even cold by the time I got to that wall.
The bubbles went away after the water dried and although I told my husband not to paint one of the walls because it needed some extra work, he went ahead and painted it.
He said that when he was painting the bubbles came up again but again, they went away once the paint dried.
I believe it is an adhesion problem with the paint underneath. Luckily (?) we live in an apartment and the long term problem won't be ours...
Thanks again, all the input was thoughtful and helpful,
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