Primer (paint)

Compared to paint, a primer is not intended to be used as the outermost durable finish and can instead be engineered to have improved filling and binding properties with the material underneath.

Priming gypsum board (drywall) is also standard practice with new construction because it seals the wall from moisture and can prevent the growth of mold.

Primers can also be used on dirty surfaces which cannot be cleaned or before painting light colors over a dark finish.

The level of exposure, such as indoors versus outdoors, may affect how important applying the topcoat within the time-frame will be.

A layer of primer will prevent the underlying wood from prematurely absorbing the solvents in the finishing paint.

Once water seeps through to the bare metal, oxidation will begin (plain steel will simply rust).

[6] Special kinds of primer (rust-converters) can be used to chemically convert rust to the solid metal salts.

In addition, primer provides a smooth surface for the paint to adhere to, resulting in a professional-looking finish.

[8] Using a primer on surfaces made of plastic is only necessary when making a drastic change of color (going from dark brown to white, for example) or when a long-lasting coat of paint is desired.

Alternative surface treatments, such as plasma activation, can replace primers in the cases when the latter are used to improve adhesive bonding between the substrate and the paint or the lacquer.

Importantly, plasma activation can be performed at the atmospheric pressure in air with fast processing speeds.