Part of this is curiosity, part is ignorance, and part might help me select the correct product.
What makes primer different? I understand some has “stuff” to hide stains or knot bleed-through. But what makes it stick better?
Alkyd is the modern oil base paint, right?
Latex is the everyday stuff.
Where does enamel fit into the picture?
And paint that touts “100% acrylic”…vs what?
Do it right, or do it twice.
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Replies
There are many whole books on the subject. Gets complicated. The pigments are different in a primer since they are not exposed and don't need to be as durable. Some primers have shellac, which is a great bonding agent. Some just have more oil and less resin so they penetrate better. Paints basically contain a pigment, a binder system, thinners, and additives. Pigment is usually titanium dioxide and chalk or talc. Other pigments for colors. Thinner is to make it brush or spray easier and level. Water or solvents depending on the type of binders. Additives speed or slow the drying time, change gloss, promote wetting, help reduce brush marks, reduce pinholes, etc. Binder system is complicated. Simplest is plain linseed oil. Not too durable. Then oil with resins - alkyd or acrylic usually. Better. Water based systems use latex, polyvinyl acetate or other binders. Some binders simply dry, like shellac. Others crosslink, like oil. The more it crosslinks, usually the tougher the final result.
"100% acrylic" uses an acrylic resin and an acrylic binder. Enamels use finer pigments and a higher binder/pigment ratio. Thinner, more gloss, and less hiding power. Everybody says their brand is the best. Price is sometimes a good indicator. If it costs $5 a gallon it won't be great. If it's $40, probably pretty decent. In between, it's anybody's guess. As a general trend these days, I'd say water-cleanup paints are getting better and oil-based are getting worse because of the restrictions on volatile organic thinners.