The Differences Between Interior and Exterior Paint

You may not think there’s much difference between interior and exterior paints. They look pretty similar, right? But there are significant differences owing to the how they are applied and how they need to perform.

In a previous blog post, I discussed the basic components in paint and why premium paints are more expensive than cheap paints. The main ingredients of any paint (interior or exterior) are pigments, solvents, resins, and additives. Pigment is the color which is bound to the surface by resin. The solvent is the liquid which allows the paint to be spread with a brush, roller, or sprayer. Additives are used to change the performance of the paint (e.g. make it easier to apply or make it mildew resistant).

In latex paints, the solvent used is water and in oil-based paints, mineral spirits. Water- or oil-based paints can be used outdoors, but oil-based paints are typically not used indoors because of the odor and the difficulty to clean up.

Organic pigments are typical in interior paints, but certain types of organic pigments are prone to fading with prolonged exposure to sunlight and excessive heat. As such, exterior paints will usually be formulated with synthetic pigments for longer color retention.

Acrylic or alkyd binders are most commonly used in residential paints. They can be formulated to behave differently over time. Most interior paints offer better abrasive resistance, making them easier to clean. The resins in exterior paint are formulated to resist cracking and chalking and bind the pigments for longer color retention.

Some other differences in interior and exterior paint resins include the amount of flexibility required for exterior paints to accommodate expansion and contraction of substrates. Exterior paints are formulated to cure with the help of sunlight, whereas interior paints are not.