There are three basic ingredients that make paint work - pigment, binder, and thinner. Pigments give paints their color and allow them to cover the substrate. The binder is the "glue" which holds the pigment to the substrate. And thinner is what makes the paint liquid. As the thinner evaporates, only the binder and pigment are left as a solid layer over the substrate.
Like primers, there are two types of paint - latex and alkyd. The main difference between the two is the thinner. In latex paints, water is used as the thinner - while in alkyd paints the solvent is paint thinner or mineral spirits.
Latex paints can be used for both interior and exterior applications and are the most popular and widely used paints on the market. Latex paints dry more quickly - usually within a half an hour of application and have less odor than alkyd paints. And because tools can be cleaned with soap and water, clean-up is not a problem. Interior latex paints have a smooth, blended consistency that usually eliminates any need for thinning - it can be used straight from the can. Exterior latex paints resist blistering and peeling and offer excellent color and gloss retention.
Alkyd paints, like latex paints, are used in both interior and exterior applications. Alkyd paints are durable, adhere and flow well, and leave few brush marks. Alkyds dry more slowly than latex paints and create a smooth, non-sticky film. Alkyds also have a more noticeable odor and require a solvent to clean-up any brushes or tools. Exterior alkyd paints differ in composition from ones designed for interior use. The binder used in exterior alkyds does not dry as hard as the binder in interior alkyds. Because of this, exterior alkyds are more flexible than interior alkyds and enable the paint to withstand extreme temperature and humidity changes, as well as increase the life of the paint.
For maximum exterior durability, an alkyd primer and two finish coats of a high quality latex paint is your best solution.
The appearance of the dry paint film is referred to as the paint finish. There is a wide range of finishes for both latex and alkyd paints. And the type of finish directly affects the cost of the paint and its durability. The most common types of finishes are: flat, satin or eggshell, semi-gloss, and gloss.
Flat finishes create a soft, uniform, light-diffusing appearance. On exterior surfaces, a flat finish is popular on shingles and rough siding because it hides many surface defects. On interiors, a flat finish diffuses the light, hiding minor imperfections. Flat finishes are also the least expensive type of paint finish.
Satin or eggshell finishes have a low lustre and are excellent for high use areas where a scrubbable finish is desired such as family rooms, hallways, and children's rooms.
Semi-gloss finishes are ideal in areas where durability and scrubbability are important. Because of its resistance to soil and wear - recommend semi-glosses in areas where extra protection is needed.
Glossy finishes dry to a bright and shiny finish that's easy to maintain. Glossy's can be used on wood, plaster, metal, or any other smooth surface inside the house. Exterior applications, however, are more limited - just usually for shutters and trim.