Red Green:

About "100% Acrylic" paint.

Most people that throw that term around don't really know what it means, but presume it's a measure of quality in some respect or another. The paint manufacturers that slap "100% Acrylic" on their paint cans are exploiting that lack of public understanding to help sell their paint.

In North America, over 90 percent of the latex paint that's made is made from one of two different kinds of plastics.

1. Polymethyl methacrylate - which you probably know better as "Plexiglas" or "Lucite" or "Perspex", depending on which chemical company made it. In the paint industry, latex paints and primers that consist of gazillions of tiny hard spheres of this kind of plastic suspended in a solution that is mostly water are referred to as "100% Acrylic" paints, or paints with "100% Acrylic" resins.

2. Polyvinyl Acetate - which you probably know better as "PVA" or white wood glue. In the paint industry, paints and primers that consist of gazillions of tiny hard spheres of this kind of plastic suspended in a solution that is mostly water are referred to as "Vinyl Acrylic" paints, or paints with "Vinyl Acrylic" resins.

3. Some interior high gloss paints are made from a styrenated acrylic plastic, but styrenated acrylic paints are more popular in Europe than they are in North America, and I don't know why.

Note that there is no such thing as a "50% Acrylic" paint or a "75% Acrylic" paint or even a 99.9% Acrylic paint. It's either "100% Acrylic" or "Vinyl Acrylic" or "Styrenated Acrylic". There is no benefit to be had in in mixing different kinds of plastic resins in the same can of paint, and doing so would only make formulating the paint more complicated because each different kind of plastic resin require different kinds of coalescing solvents, additives and rheology modifiers.

The problem with this naming system is that people presume that if a paint is 100% Acrylic, there's no point spending more on a higher priced paint because you can never get higher than 100%, right? Really, the wording "100% Acrylic" on a can of paint means about as much as the wording "100% Cow" does on a package of meat. It tells you the kind of plastic the paint is made of, but that's all. You don't know if you're getting prime rib or dog food.

Generally, "100% Acrylic" latex paints are more expensive than "Vinyl Acrylic" paints, and they:
a) have better resistance to acidic and alkaline substrates like fresh concrete
b) have better UV resistance
c) dry to harder and more marr resistant films that stand up better to hard scrubbing,
d) stick better to damp or moist surfaces, and
e) don't exhibit any "blocking" which is when a paint remains slightly sticky after it's fully dry.

Essentially ALL exterior latex paints will be made from polymethyl methacrylate because of it's better UV resistance and the fact that the film doesn't soften up and lose it's adhesion if it gets wet like polyvinyl acetate paints and primers.

The problem with polyvinyl acetate paints and primers is that they have lousy Alkaline resistance, lousy UV resistance and they lose their hardness and start cracking and peeling if they're used in a wet or highly humid environment. Also, they have poor "blocking" resistance in that an apparantly dry paint film will still retain some residual stickiness.

If you ever look in someone's bathroom and see that the paint is cracking and peeling on the ceiling above the shower, the problem is almost always attributed to poor surface preparation prior to painting, but that's a misdiagnosis of the problem. It's the fact that a PVA paint was used on that bathroom ceiling, and probably on the bathroom walls too.

Also, if you've ever had doors and windows that tend to "stick" when they're closed, the usual cause of that is a PVA paint being used on them. When a door painted with a PVA paint closes and presses gently against a frame painted with a PVA paint, the two will stick to one another. Again, the fix is to paint over the "vinyl acrylic" paint with a "100% Acrylic" paint to prevent the door from sticking to the frame. It's the same thing if you've ever rested your head against a painted wall and found that your hair ended up "sticking" to the paint. In that case you have the poor blocking resistance of a PVA paint combined with it's poor moisture resistance. The result is a slightly sticky paint softening up due to the moisture from your scalp and causing your hair to become embedded in the soft sticky paint.

There are literally hundreds of different "100% Acrylic" resins used to make primers, paints, floor finishes, grout sealers, water based "varnishes" and nail polishes for the ladies. And, there are hundreds more "vinyl acrylic" resins used to make mostly primers, budget priced interior latex paints and of course, wood glues. So, specifying a "100% Acrylic" paint is no more precise than specifying "cow" when you order a hamburger. Every paint or primer made from tiny spheres of polymethyl methacrylate is a "100% Acrylic" product, but 100% Acrylic resins vary quite considerably in their properties and their price. That's why it's been said: You get what you pay for when buying paint.