Whether touching up your shutters or making a decorative change in the spare bedroom, it is important to choose the correct type of paint. Indoor (or interior) and outdoor (or exterior) paints are made of different components and are not interchangeable. Using the wrong type of paint on a surface can dramatically affect how well the surface takes the paint and how long it lasts, and it can be dangerous to use the wrong kind of paint.
Exterior paint is either latex or alkyd and is very flexible, which keeps it from cracking, mildewing and fading, since materials used outdoors will expand and contract due to weather conditions. Interior paints are water-based or oil-based. Water-based interior paints have less odor, are not flammable and dry quicker, while oil-based interior paints are better for penetrating porous surfaces, have superior wearability and can create a smoother finish.
Generally, interior paints are available in the following sheens or lusters: flat, low luster, satin, semi-gloss and gloss. Sheens and lusters describe how shiny or glossy a paint is, with flat being the least shiny and gloss the most. Gloss indoor paint is easier to clean, but it can call attention to any material flaws. Satin is rather stain-resistant and is also easy to clean, making it ideal for indoor walls. Exterior paints are usually available in flat, semi-gloss or gloss lusters. The exterior paint you choose depends highly on the surface you need it for, like aluminum siding, wood, brick or stucco. Latex is easier to work with and dries quickly, but alkyd paints are more durable and better for less-than-optimal surfaces.
Interior paint tends to fade more quickly in the sunlight or under water duress, like rain, snow or being sprayed by a hose, because it is intended to be used in a climate-controlled environment. Exterior paint is less washable, as it is made to withstand the weather. Interior walls that are exposed to a large amount of sunlight may need an extra coat of paint.
Exterior paints are made with more VOCs, or volatile organic compounds. VOCs create odors and fumes that last months longer than interior paints'. Using exterior paints outdoors is fine, as there is plenty of ventilation and the fumes won't bother you, but since VOCs cause headaches, nausea and light-headedness, it is important not to use an exterior paint indoors.