Automotive primers come in four colors that help differentiate them from one another. Some primers are used for vehicle repair or rust prevention. Primers can also be tinted the color of the car to help reduce the number of paint coats needed to fully cover the car. These primers are used on multiple-stage paints that require thinner coats, such as pearl and candy custom paint.
Black automotive primer is used primarily on vehicles that have a black topcoat of paint. This allows the painter to use fewer coats of black and provides a much deeper, more vibrant color. Black automotive primer can also be used on other dark colors, particularly on paints that require several coats of paint, metallic or candy coating (a custom paint that has a shimmery effect similar to that of hard candy). It can also be used on a clear coat to achieve the desired paint effect. Because too many layers of paint can easily crack rather then bend or flex (as is desirable), using a single thin coat of black primer lets a thinner coat of paint offset the thickness of the metallic or candy and clear coats.
White or gray automotive primer is used in the same way as black primer. On cars with lighter-color paint jobs, particularly white, it is sometimes necessary to reduce the amount of primer and paint used. This reduces the number of clear top coats needed to replicate factory finishes. Because thick paint or clear top coat is very hard when dry, using fewer coats of paint and clear top coat prevents chipping or cracking of the clear top coat.
Red automotive primers are primarily used to differentiate what are called filler primers from ordinary primer types. Filler primer is used in auto body repair to smooth out dents that have been repaired. Unlike other primers, filler primer is sanded smooth before applying the top primer coat or paint coat.
Tinted primers, while similar to black or white primer in use, are created differently. While black and white primer are available from paint stores, tinted primers must be tinted to the color of the car before being applied. This is particularly important on multiple-stage custom paint jobs where there are far more coats of paint than on a typical car, increasing the risk of the paint job cracking or chipping. To create tinted primer, the painter begins with white or gray primer and then mixes the actual paint to be applied to the car without adding the metallic or candy effects. The painter then adds small amounts of the paint to the primer until the shade of primer is roughly the same color as the paint.
Green primers that have a more transparent quality than other primers are called "self-etching" primers. These primers are used exclusively on bare metal to help prevent rust when the panel is painted. Automotive companies first bathe new cars in this type of primer before painting and assembly to help prevent rust.
