There may be several objectives for coatings; however, the most important objective in engineering applications is to protect a structure against corrosion. This is achieved by the following means:

• Resistance to environment: The paints offer a substantial resistance against penetration of aggressive environmental species which may cause corrosion. This would largely depend upon the type of coating selected and its compatibility with environment. For instance, a bitumen coating would be compatible for water immersion and a coating containing an inhibitor such as chromate for industrial atmosphere. The thickness must be designed taking into consideration the corrosive environment.

• Electrical resistance: Because of the high coating resistance, the corrosion current is reduced and the rate of corrosion assumes a very low value. This is however a function of coating components.

• Inhibitive pigments: By selection of inhibitive pigments, corrosion is inhibited. For instance, the addition of red lead, zinc chromate and calcium plumbate inhibits both the anodic and cathodic reactions.

• Cathodic protection: Coatings containing zinc as pigments, cathodically protect the surface by releasing electrons.