Four basic elements make up a paint system (a system approach recognizes the interdependence of these individual elements):

1. Surface Preparation
   
   Mainly performed for cleaning the surface (removal of contaminants), improved wettability and roughening the surface to anchor paint (profile, anchor pattern, tooth). Further information related to steel is available on the SSPC web site at: www.sspc.org 

2. Pretreatment
   
   Mainly performed for enhanced paint adhesion and improved corrosion resistance (for example phosphate conversion coatings, wash primers). Follow the technical info link to a comprehensive article on metal pretreatment on the web site of the British Surface Treatment Suppliers Association at:
   http://www.bstsa.org.uk/

3. Primer(s)
   
   Important functions include wetting the substrate surface, linking the topcoat to the substrate (adhesion) and providing corrosion protection for the substrate. The significance of the primer in corrosion protection is often underestimated.

4. Top Coat(s)
   
   Often with a mainly decorative function but functionality may also include UV resistance, chemical resistance, abrasion resistance, reflectivity, moisture resistance, etc.

References/Literature:

Links:

Main components of a paint coating

Paint adhesion mechanisms

Effect of Surface Treatment on Paint Durability

Reliability factors - paint coatings on steel

Some paint coatings are smarter than others ...