Primer is applied directly onto the bare metal to prevent corrosion and promote adhesion of the next paint coat. It is generally applied as a very thin coat and does not require sanding. There are several kinds of primer. However, a pure primer is less often used today in repairs and repainting, because a new product, primer-surfacer, has been developed to replace it.

Also sometimes called wash primer. Etching primer mainly consists of vinyl butyral resins and zinc chromate (rust preventive pigments) and an additive with phosphoric acid as a main base resin. Etching primer is available in two types, a single-component type and a dual-component type. The dual-component type wash primer provides better rust preventive. Etching primer must be applied very carefully because its adhesion power reduced if applied too thick or left to dry more than necessary.

A dual-component type primer mainly consisting of alkyd resins. It hardens when mixed with isocyanate (hardener). Urethane primer provides outstanding corrosion protection and adhesion power, but requires hot air around 140 °F (60 °C) for drying. Drying under normal temperature 68 °F (20 °C) or below is a very slow process.

This is a dual-component type primer mainly consisting of epoxy resins. It hardens when mixed with an amine family hardener. Similar to urethane primer, it also provides outstanding corrosion protection and adhesion power and requires hot air around 140 °F (60 °C) for drying. Drying under normal or low temperatures is a very slow process.