Paints and Painting
The term paint is used to describe a wide variety of coatings which are applied as a liquid and subsequently dry to form a durable decorative and apparently solid film. Paint is a very versatile coating medium — it can be used on almost any surface no matter how intricate, and can be applied in a number of different ways. You can classify paints by use or by their binder:
Paints by binder
Traditionally, paints were based on oil such as linseed which dries to form a solid paint film. Nowadays, the linseed has largely been replaced by better synthetic resins called alkyds. These paints are available in matt, satin and full gloss finishes and, as a whole, are more durable than polyurethane paints on exterior woodwork.
Polyurethane (oil based)
Many gloss paints and clear finishes for wood — varnishes, for instance—contain polyurethane binders or urethane-modified alkyds. Most of these paints—in particular the glosses — are thixotropic: they are jelly-like in the can but become liquid when shaken or stirred and are less likely to drip than other types. As a general rule, polyurethane gloss paints are not as glossy as alkyd gloss paints but are quicker drying, particularly tough, and have a reputation for excellent abrasion resistance.
These are available in matt, eggshell, satin and full gloss finishes, though the most glossy emulsion finishes do not produce as much shine as polyurethane or alkyd gloss paints. The most popular emulsion paints are based either on a resin called polyvinyl acetate (for short) — giving rise to the term vinyl which is often found on paint tins — or on acrylic copolymers. Most emulsion paints can be washed once they are dry and can be used in areas affected by condensation, such as bathrooms or kitchens. Some inexpensive emulsion paints have very poor resistance to water — rubbing these with a damp cloth rapidly removes the paint and condensation can cause the paint film to become brittle and then flake off. Painting over these paints (even with a water-resistant paint) may prove troublesome — the ‘new’ paint may be difficult to brush out and the original paint may tend to lift off the surface beneath.