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THE PARTS AND FUNCTIONS OF PAINT SYSTEMS
Painting of building is an accepted method of protecting many building materials against
Corrosion. Wear decay and other factors that effect durability. Painting can also provide finishes which are hygienic in the sense that they are resistance and readily cleanable. Beyond this function, paint is of course widely used to produce decorative effects.
In order that the paint may perform these functions satisfactorily, remain free from defects, and have a maximum useful life, it is essential that:
1. the surface is brought into a suitable condition to receive the paint;
2. appropriate paints are selected for the particular purpose, i.e., having regard to the nature of the surface are to be painted, the functions the paint is required to perform and the conditions of exposure;
3. each coat of paint used be suited to its own particular function in the paint system; and
4. the paint is to be properly applied in an adequate number and thickness of coats with the necessary degree of skill and excellence.
In most painting systems two or more different coatings are involved each having a special function such as primers, undercoats, and finishes.
a) PRIMER :
The general requirements of the first coat of paint on any unpainted surface are that it should adhere firmly to that surface and provide a suitable ground to receive and hold the next coat. The surfaces of building materials, however, differ widely in their physical and chemical characteristics and on some of them the priming coat is required to fulfill important additional functions. It is essential;
Therefore, select the right type of primer for each material.
b) UNDERCOAT
The chief function of paints used for undercoating are to obscure the primed surfaces to provide a fresh surface of uniform absorption and of color approaching that of the finish coat, and to help to build up a layer of paint sufficient in thickness to protect the material painted, according to the conditions of exposure, when used in conjunction with a suitable finish coat.
c) FINISHES :
The final coat in a paint system is intended to provide the particular color, and degree of gloss or texture required, but it can only do so if the previous work has been carried out properly. If for example, the porosity of the absorbent surface is not completely satisfied by the priming and undercoats the finish is likely to have a patchy appearance due to local absorption of the medium again. Gloss paint is somewhat translucent and will not itself hide in equalities in the color of the underlying materials, where the contrast is too great.
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