Primers go on sanded walls before the interior paint topcoat. Acrylic latex paints are most expensive, but best for most cases.
Primer is a layer of paint that goes straight on the wall. The primer is usually thick and fills some imperfections of the surface. It has a matte, toothy (flat) texture to make painting with actual interior paint (topcoat) easier. Bonding primer adheres to shiny surfaces like glass, tiles or glossy paints. It is interior-use only, beacuse it is not flexible and can chip with exposure. All-purpose primers are either oil- or latex-based, the latter is more expensive and considered better; the former is not recommended for drywall. Stain-blocking oil-based primers work better with water, crayon, with any spot priming. Latex-based stain-blockers work better on larger areas and on outside. Stain-killers block odors from animal urine as well. Stains, odors, and wood oils in pine or cedar can bleed through topcoat and through all-purpose primer.
Interior paint has binder, pigment, thinners and additives. Most commonly used interior paints have either acrylic latex binder (resin) with water for the thinner, or alkyd oil paints with mineral spirits thinner. PVA, or polyvynil acetate resin interior paint is also water based. It is twice cheaper than acrylic latex and not as durable. PVA based interior paint doesn't foam as much as acrylic latex paint and easier to apply. Oil interior paint tolerates dirty, chalky, and not quite prepared surface better than other paints. Oil paint tolerates freezing temperatures better than acrylic. Polyurethane paint used on concrete is different from polyurethane paint used in automotive.
Texture: Gloss paints have very smooth and shiny texture and binder to pigment ratio 80% to 20%. They wash very well. Gloss interior paint shows every scratch and dent, while flat interior paint softens the appearance of uneven surface and hides imperfections; binder to pigment ratio is 30% to 70%. Egg-shell, satin and semi-gloss interior paint textures fall in between. Flat paints have pigment particles exposed, with very thin film of binder. Washable flat paint is more expensive, because it needs better binder to be washable.
Pigment: hiding pigments are titanium dioxide (white) and other mineral and organic pigments. Non-hiding pigments are talc, clay and silica. Paints vary in hiding to non-hiding pigment ratio.
Interior paint is sold by quart, by gallon and by five-gallon backet. Labels have specific instructions and coverage estimates, typically in hundreds of square feets per gallon.
See also: kitchen countertops.