Wet Paint Peels Away from Primer

[Surfing Bird]

Please help. After spackling, sanding, vacuuming and washing with a light solution of Spic & Span, I primed interior walls & ceiling with 2-year old Glidden Interior/Exterior Gripper Primer Sealer, originally white with some gray color added to it. (This same mixture was used successfully outdoors 2 years ago.) Several days later I painted a top coat with Glidden Interior Premium Paint, Satin Finish latex. Several days later I painted another coat for better coverage and, when dry, noticed some areas that were noticeably less "satin" than the surrounding area. Figuring I had been careless when painting the second coat, I decided to try "fixing" the unglossy parts before going into a full repaint. When doing this I noticed a fiber in one small wet area and tried gently to remove it with the thought that I would then smooth out that area with a bit more paint. Instead, the two dried coats of latex virtually slipped away from the primer coat as easily as the clear film that is used on appliances to prevent scratching in transit. I was able to cleanly peel away all paint layers in the entire wet area up to the area of paint that I hadn't recovered. What gives? The new wet paint seemed to almost instantly melt the two completely dry underlayers. Needless to say, the "fix" didn't work, so I'm afraid to try an entire third coat. Will I have to reprime? But with what, since I don't know what went wrong here. Can someone clue me in? Thank you.

[HayZee518]

latex paint

latex paint should go over virtually any paint without problems because it is basically water based. Oil based has solvents other than linseed oil to make them fluid. MEK or methyl ethyl ketones, toluene, mineral spirits and turpentine are the most common components in paint and varnish remover and dissolves what's underneath. it will curl latex and varnishes. for a primer, an alcohol based primer like ZISSNER "KILZ" would be better.

[Nestor]

Improper film formation

Surfing Bird:

The fact that you noticed that some areas of that second coat had dried to less of a gloss ("noticeably less satin", as you said) is significant. It means that the second coat of satin latex paint never formed a film properly in those areas that were less glossy. And, that, in turn means that the second coat of paint wasn't sticking as well as it should have in those areas either.

It could be that the wall was simply too cold (because of cold outdoor temperatures) for the acrylic resins in that second coat to have coalesced properly, or it may have simply been too humid in the room for the water to have evaporated from the paint.

I would advise you to simply wait for what you have to completely dry, and then remove any paint that isn't sticking well. You can use painter's masking tape (or possibly even regular masking tape) to test the paint adhesion all over the area you painted. And, wherever you find that the paint comes off with the tape, use the paint scraper to remove as much paint as will come off in that area. Then, repaint when you have warm temperatures and can allow the paint to dry with the windows open.

I can't say what caused the paint not to form a film properly, but I can explain how latex primers and paints form films, so that you would understand the process and at least be better able to figure out what may have gone wrong if this ever happens to you again:

Latex paint is a SLURRY, which is a mixture of solid particles suspended in a liquid.

There are three kinds of solid particles in latex paint:

1. the coloured pigments (these are tiny pieces of rock or plastic that vary in size, but generally range from about 1/500th the size of a red blood cell all the way up to the size of a red blood cell. They are what determine if you have yellow paint or blue paint or reddish brown paint).

2. the extender pigments (these are huge rocks almost large enough to see with the naked eye. The limit of unaided human vision is about 20 microns, with a micron being a millionth of a meter, or 1/1000 of a millimeter. Extender pigments vary in size from that of a red blood cell (5 microns) all the way up to about 30 microns, or about 1/3 the diameter of a human hair. It's the size and amount of extender pigments that determine whether your paint dries flat or to a high gloss or to something in between. Were it not for extender pigments, ALL house paints would dry to a high gloss.)

3. the binder resins (these are tiny pieces of colourless transparent or transluscent plastic which in most latex paints are about 1/50th of the size of a red blood cell, or 1/10th of a micron in diameter. The binder resins are the most expensive component in latex paints, which is why flat paints which contain less binder and more extender pigments cost less that high gloss paints that contain more binder and less extender pigment.)

There are two kinds of liquids in an UNTINTED can of latex paint. The carrier fluid in paint tinting colourants is glycerine, so glycerine is also added when tinting the paint to the desired colour. The two liquids in an untinted can of latex paint are:

4. a slow to evaporate water soluble solvent called a "coalescing agent" or "coalescing solvent" (which in many modern latex paints is a chemical called "Texanol" made by the Eastman Chemical Company) and,

5. Water.

When you spread the paint on the wall, the first thing that happens is that the water starts to evaporate. As the water evaporates from the wet paint, the clear plastic binder resins find themselves surrounded by the coalescing solvent at an ever increasing concentration. The coalescing solvent permeates the plastic resins causing them to get soft and sticky. (Think of the coalescing solvent as dissolving (kinda) the binder resin plastic so that it becomes soft and sticky.) The forces of capillary pressure and surface tension, (which are what cause tiny water droplets in clouds to coalesce to form large rain drops) then cause each soft sticky plastic binder resin to stick to and pull on it's neighboring soft sticky plastic binder resins, causing the wet paint to transform into a continuous film of soft sticky plastic with the coloured and extender pigments suspended inside it much like the raisins inside raisin bread.

(Incidentally, in case you ever wondered why latex paints darken as they dry, it's exactly the same reason that snow is white, but melted snow, or water, isn't. It's because as all those individual plastic binder resins coalesce into a solid film of clear plastic, you have progressively less and less reflection and refraction of incident light, which your eye sees as "white" light. So, as the plastic binder resins coalesce, you see less and less white light coming from the latex paint, and so it darkens in colour as it dries. That's why they'll have a hair dryer at every paint store to dry paint quickly to confirm it's drying to the right colour.)

It's when these binder resins are soft and sticky that adhesion of that plastic film to the wall occurs. The higher the concentration of coalescing solvent in the binder resins, the softer and stickier the resulting plastic film, and the better the adhesion of the paint film to the substrate (all other factors being equal).

Then, after "coalescence" of the binder resin has resulted in a soft film of plastic sticking well to the wall, the coalescing solvent gradually evaporates from the paint and filling the room with that "freshly painted smell". And, as the coalescing solvent evaporates from the paint, the soft plastic hardens back up again in 3 or 4 days to a little harder than the plastic was when it still consisted of tiny particles of plastic inside the can.

Now, what could go wrong?

If you were painting exterior walls on a really cold day, then the cold temperature of the wall would have slowed the rate of water evaporation from the wet paint and kept the plastic harder than it would otherwise be. The result might be the binder resins being too hard to deform sufficiently under the forces of capillary pressure and surface tension to form a continuous film of plastic that stuck well to the wall. Instead of solid plastic, you could have gotten anything from a plastic film with gazillions of tiny air pockets in it to something that would look like cooked rice under a microscope where the binder resins have hardly changed in shape at all, and are just sticking to one another about as poorly as they're sticking to the wall. If the paint was coloured (like red paint or blue paint), you'd immediately notice that the paint would have a white discolouration to it because of light reflecting and refracting off all those air/plastic interfaces inside the paint film (which is why clouds are white). That is, the dry paint would be about the same colour as the wet paint, but typically with a lot of unevenness in the amount of white discolouration.

If you were painting a ceiling during wet weather, then the high outdoor humidity air would keep the indoor humidity high, and the warmest most humid air which would be trapped under the ceiling. That humid air would prevent the water in the painted ceiling from evaporating, but not the coalescing solvent, and again we can end up with the binder resins not becoming soft enough to deform sufficiently or stick well because the coalescing solvent was evaporating over the first 24 to 48 hours while the water in the paint wasn't.

Glycerine is the carrier liquid in paint tinting colourants because it's equally soluble in both water and mineral spirits. So, the same paint tinting colourants can be used in a single paint tinting machine to tint both oil based and latex paints, or all the paint a hardware store sells. The problem is that glycerine is even slower to evaporate than coalescing solvent, so the glycerine in the paint film would still be "diluting" the coalescing solvent in the paint film after the water evaporated, and that would limit how soft and sticky the acrylic binder resins got. On a cold day with lots of glycerine in the paint, you can again end up with the plastic resins not softening up sufficiently for proper film formation. (The dilution of the coalescing solvent is the primary reason why you can ruin a latex paint by adding too much tinting colourant to it. Oil based paints have a completely different film formation mechanism and will still form a proper film, albeit slower, regardless of how much you tint them. That's only one of the ways oil based paints are inherently better than latex paints.)

Whenever you get improper film formation in a latex paint, the result is normally a reduction in the gloss level of the paint accompanied by a white discolouration of the dried paint and that rougher whiter film not sticking as well to the substrate. Generally, as drying conditions get progressively further from ideal, the more paint will be less glossy than it should be, the amount of white discolouration in the paint increases and adhesion to the substrate decreases.

Try removing the paint that didn't form a proper film as described earlier and give it a third coat when it's warm enough outside that you can paint with the windows open. But, at least now if the paint doesn't do what you expect, you at least know how film formation in latex coatings works, and have the knowledge needed to figure out what went wrong.

PS: From what I'm reading, you cleaned the spackle with Spic&Span after sanding it smooth and removing the dust. Since that spackle hadn't had time to get dirty, what was the motivation to clean spackle that wasn't dirty. Also, how did you prevent the spackle from absorbing that cleaning solution and getting so soft that even the sponge or rag you were cleaning with would wreck the smooth surface produced by sanding it smooth?

[bettyjmaar]

Acrylic or Latex Paint are one of the good deals to lay out a primer to color home. They long last and worked great for me as well.

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