There seems to be a misconception in here that latex paints dry slightly
sticky and a result, never fully "cure".
People should be aware that in North American 90 percent of latex paints
are made from one of two different kinds of plastic:
1. Polyvinyl acetate - which you probably know better as white wood
This plastic has poor "blocking" resistance, which in paint-lingo
means that even when fully dry, it remains slightly sticky. PVA resins
are used to make inexpensive interior latex paints and general purpose
primers. PVA latex paints also lose their adhesion under moist
conditions, causing them to crack and peel on bathroom ceilings,
expecially directly above the shower. It is no doubt this slight
stickiness that makes people think that the paint hasn't fully cured.
2. Polymethyl methacrylate - which you probably know better as
This plastic is superior to polyvinyl acetate for making paint in
every catagory except cost. Polyvinyl acetate plastic resins adhere
much better to damp surfaces, and they have much higher "blocking"
resistance, which means that the dry paint won't remain slightly sticky
or stick to itself. PMMA resins are also very much more alkaline
resistant, so primers made for painting over fresh lime based plaster or
fresh concrete will always be made of PMMA resins. ALL exterior latex
paints will be made of PMMA resins.
The idea that some latex paints never fully dry is a misconception.
They all fully dry. It's just that inexpensive latex paints made from
PVA resins will remain slightly sticky even when fully dry.
The remaining 10 percent of interior latex paints in North America are
made from styrenated acrylic resin. This kind of plastic provides good
gloss and hardness, but has poor UV resistance. Such paints are much
more common in Europe than they are in North America.