What is the Purpose of Primer?

A primer (undercoat) is a preparatory coating put on materials before painting. Priming ensures better adhesion of paint to the surface, increases paint durability, and provides additional protection for the surface being painted.

Primer allows finishing paint (topcoat) to adhere much better than if it were used alone. It is designed to adhere to surfaces and to form a binding layer that is better prepared to receive the paint. Compared to paint, a primer is not intended to be used as the topcoat but does allow for improved filling and binding properties with the material underneath.

A primer is often used when painting porous materials, including concrete and wood. Using a primer is considered mandatory if the material is not water-resistant and will be exposed to the elements. Priming 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 surfaces that cannot be cleaned or before painting light colors over a dark finish.

Some primers can be tinted to match more closely with the color of the finishing paint. If that color is a deep color, tinting the primer can reduce the number of layers of finishing paint that are necessary for good uniformity across the painted surface.