Difference Between Interior & Exterior Paint

Interior and exterior paint have different properties. Exterior paints are not necessarily stronger or tougher than interior paints. Interior paints are formulated to resist scrubbing, staining and cleaning, while exterior paints are formulated to prevent fading and mildew. It is important to use the correct type of paint for your application.

Common Attributes of Paint

All paints have four parts: Solvents, resins, additives and pigments. Solvent, which is usually in the form of water (for latex paints) or mineral spirits (for oil paints), is what makes paint wet. Lower-quality paints use more solvents than resins, additives or pigments. The solvent evaporates as the paint dries, leaving only the resins, additives and pigments on the wall. Resins bind the pigment (color) to the wall and are made of acrylic, silicone or epoxy. Additives are additional chemicals added to paint to change a property of the paint. Some additives prevent mildew or fading. Others make the painted surface easier to clean. And some make the paint chip-resistant or make it easier to apply. There is a variety of additives to suit a variety of applications. Pigment is the actual color added to the paint. It is usually added in powder form and does not dissolve but is suspended in the solvent and bound to the wall by the resin.

What Interior and Exterior Paint Have in Common

Interior and exterior paints have similar solvents and pigments, but some pigments are not suitable for exterior paints because they fade quickly. Water and mineral spirit soluble paints can be used indoor and outdoors depending on their formulation, but "oil" paints are less popular choices for interior painting because of their high odor and cumbersome cleanup. They are also regulated by some municipalities because of their impact on the environment.

Where Interior and Exterior Paints Differ

Interior and exterior paints often use different resins to bind the pigment to the painted surface. Exterior paints must be flexible to accommodate temperature changes and exposure to moisture, so the binding resins used in exterior paint often make exterior paint softer and more prone to scuffing. Exterior paints have to be highly durable with an exceptional resistance to peeling and chipping. Interior paints are not exposed to huge temperature changes or excessive moisture so the resins used to bind the paint to the wall can be more rigid. This can help the paint be less prone to scuffing and easier to wash.

Unique Additives

Interior paints are formulated with additives that make it easier to clean, scuff-resistant, stain-resistant and with good hiding ability. Exterior paints are formulated with additives that make it durable, and resistant to mildew and fading.

Use the Right Paint

Many people think exterior paints offer better long-term results when used indoors, but this is not true. Exterior paints are often softer and more prone to scuffing. They are high-odor and release more VOCs (volatile organic compounds) than interior paints while they cure. They are not as washable or stain-resistant. Conversely, interior paints are not a good choice for outdoor projects because they are prone to peeling when exposed to temperature flux and moisture, and can mildew.

References

• Choosing the Right Paint