Paint is a term that can describe various coatings that are applied as liquids and then dry to form durable, solid and decorative films. Paint is a versatile coating medium. It could be used on any surface and could be applied in various ways.
Most paints have three ingredients, a binder, pigment and liquid. The opacity and color of paint are because of the pigment. This could impart the best of protection for other ingredients by absorbing destructive ultra violet light. Whitewash is the easiest paint which is basically a coating of just pigment like case chalk. Whitewash doesn’t offer too much protection to any surface though since it doesn’t contain binders. Binders hold pigment together and help it stick to any surface. Binders are usually solid, so producing a paint that could be spread over uneven surfaces will involve breaking down the binders and suspending them in liquids.
Paints by use
An ideal paint needs to satisfy various criteria. It needs to stick to a surface strongly, cover it well, leave a desirable and decorative finish, and needs to last, particularly outside. There is no single paint which can perform all of these functions at the same time. Most paints are formulated for a specific use.
Sealers and primers
These need to be used for exposed or new woodwork, metalwork, brickwork, plaster, etc. They stick firmly to surfaces, seal and also provide a base for further coats. They need to be used when painting over old paintwork with different paint too. In such situations, they will prevent chemical attacks between the paints and reduce the chances of the new paint not sticking or the old paint bleeding through.
Primer isn’t sufficient protection for any surface on its own though. It needs to be painted over.
You normally use these right after a primer when significantly changing colors. They are designed to offer good opacity and hiding power so that dark colors can be covered with lighter ones without the need of applying multiple coats. They also offer high build capacity so you can put thick coats of paint on corners or sharp edges where the paints are usually spread thinly.
These are dual purpose paints that provide a protective and decorative final coat. They are usually available in a choice of eggshell, matte, satin or full gloss finishes. This choice will affect the end appearance of your paintwork as well as durability.
There are certain modern paints like microporous paint and preservative wood stains which are designed to act as a primer themselves. With such paints, you would only need one coat or two at the most.