Metal surfaces are quite reactive, and the resultant oxide layers that form on the surface affects its outer appearance as well as performance. Metals are far more vulnerable, to exterior exposure damage without some form of protection. Rusting is a widespread phenomenon observed in steel, and steel is widely used in buildings. Rust is an oxide layer that is formed upon exposure of the surface to air and moisture, i.e. to oxygen and water. Rusted Layer is more active to oxygen and water, thereby causing the metal underneath to corrode further.
The rate of degradation of metal rapidly increases with the severity of the exposure. Paint is the most common and widely used material to protect metals. Protective paint systems usually consist of primer, undercoats and finish coats.