A.   BASE OF APPLICATION

The paint must be of the correct consistency to be applied easily by whatever method is adopted. Brushing requires one viscosity, spraying another and dipping yet another. Each paint ha to be adjusted to the particular method of application and conditions under which they are to be used.

B.   DRYING SPEED

The paint must dry in a convenient time. When a large area is being painted, the painter must be to overlap the blend areas of paint as he progresses down the surface. On the other hand, it must not dry so slowly that it slows down processing.

C.   ADHESION

The paint must have good adhesion, i.e. it must stick to the surface. The surface must be clean, so that the paint wets up properly. If it is a dusty surface, paint may come away later, a rusty surface, if painted without proper perparation would soon fail due to the detachment of the rust.

Some paints stick better than others because they wet the surface better, other because of chemical action between the paint and surface.

D.   STRENGTH OF FILM

The film must be hard and yet flexible enough to cope with expansion. Hard films are often brittle film do not lastlong. Temperature changes cause expansion, cracking, flaking and, finally, may result in complete removal of paint film.

E.    DURABILITY

The paint must retain its properties over a long period. If it does not, the gloss may disappear, the surface powder and wash off, the colour fade or darken.

The action of light, water, air and chemicals in the air may break down the film by attacking the pigment (colour change), of binder (cracks or chalking). If too much pigment is present, samll amounts of binder breaking down and a chalky appearance is produced.

Colour fastness usually depends on the quality of the pigment selected. Film integrity usually depends upon the binder, some binders have good resistance to cracking (alkyds) or good gloss retention (acrylics) or prone to chalk (epoxies).