What’s The Difference Between Interior and Exterior Paint?

Difference Between Interior and Exterior Paint

If you are thinking about starting a painting project, you know there are so many types of paint to choose from. Before you can even consider color and finish, you first need to decide to use interior or exterior paint. But what’s the difference?

The difference between exterior and interior paint is the type of resin used to bind the pigments. Exterior paint is made of weather, mold, and mildew resistant resin, while interior paint is made of softer resin resistant to cleaning products and staining. The harsh resin of exterior paint can become toxic over time if used indoors.

What Exactly Is Paint?

To understand the difference between interior and exterior paint, you first need to know the components of all paints. All paints contain pigments, solvents, resins, and some additives. Pigments are the colors, which are bound to the resins. Common resins are acrylic, epoxy, and silicone.

The solvents are the ingredients that make the paint wet and then evaporate as it dries. There are water-based paints, like acrylic and latex, where the solvent is water. There are also oil-based paints with mineral solvents. However, oil-based paints are not typically used anymore as they are harsher smelling and cannot be cleaned with water.

Finally, all paints contain certain chemical additives. As you will see below, many exterior paints are supplemented to help them last longer. For example, they might contain mildewcides and fungicides that help resist mildew and fungus. They can also contain UV-blocking chemicals to help prevent fading.

Comparing Interior and Exterior Paint

Now that you understand the composition of paints, we can delve into the specific qualities of interior and exterior paints. Below is a chart comparing interior and exterior paint to help you choose which is best for your project.

Interior Exterior
Main Function Interior paint is designed to resist staining and stand up to regular cleanings. Exterior paint’s main function is to stand up to the weather. It should resist fading from the sun and be waterproof to prevent mildew.
Water or Oil-based Solvent Oil-based paints are not typically used indoors because they are more odorous and harder to clean. Either is fine. Typically exterior paints contain more additives to help with waterproofing.
Resin Choices Interior paints contain harder resins, which allow them to be more durable to scuff marks. Exterior paints have softer, more flexible resins, which allow them to withstand wider temperature changes, as well as exposure to moisture and the sun.
Health Concerns Interior paints are safer to use in enclosed spaces. However, when painting, always ventilate the area until it is fully dry. Exterior paints typically release more gasses that you would not want in your home. Also, some of the additives can trigger allergies and smell bad.

Choosing the Right Paint for Your Project

As you can see in the above chart, interior and exterior paints are each designed to serve unique purposes. These functions will help you choose which makes the most sense for your space. You may also want to consider the different finish options available, and that is coming up next.

If you are painting an indoor space, keep in mind that certain resins and oil-based solvents can be unsafe. These paints contain harmful gasses, called Volatile Organic Compounds or VOCs, which continue to be released in small amounts for years. Even if you can no longer smell them, they will still be present and dangerous to your health.

For outdoor projects, acrylics (and latex paints with acrylic resins) are the most popular options for exterior paints. Acrylic is a very flexible material that can respond to changes in temperature without cracking. You can expect exterior acrylic paint to last five to ten years. Latex is also very waterproof, making this a great weatherproofing option.

What about the Paint’s Finish?

One final and very important consideration we have not yet touched on is the finish. The paint’s finish, also called sheen, is the amount of light that it will reflect. As you can imagine, this greatly affects the aesthetic and feel of how the paint looks in your home. There are a few different paint finishes to consider, and each has its own advantages and disadvantages.

Paint finishes typically range from flat, or matte, to high gloss. A satin finish is right in the middle. The glossier the paint, the easier it is to clean. This is because it is more waterproof. Flat paint, in contrast, can smudge easily if you are too rough when cleaning it.

Though glossier paints are more durable, there is a downside. Since they reflect so much light, you can see scratches very easily. Flat or even eggshell finishes are much better at camouflaging imperfections. When choosing a finish, consider how high traffic the area is and weigh which features are most important to you.

Exterior paints do not typically have as nice of a finish, since their primary function is to stand up to weather. Interior paints, on the other hand, can have very high-quality finishes. Cheaper paints tend to chip easily and will not last as long. Therefore, superior paint is a good investment and well worth its cost.

What about Interior/Exterior Hybrid Paints?

There are paints specifically made for both interior and exterior uses. This hybrid paint is a mixture of both water and oil, which helps it stick to any surface. It is also a low odor and low VOC in order to be safe for inside usage.

This paint is a great option, for example, if you have an indoor/outdoor area. It will have the durability of interior paint, while still being able to resist the sun and weather. However, you do not want to use this paint for all projects.

There are some tradeoffs to this interior/exterior paint. For one thing, it is more highly flammable than other paints. It also can be harder to apply, since it can splatter easily. Finally, it is worse for the environment and excess needs to be disposed of as hazardous waste. Therefore, if you do not need this versatility, you should pick a paint specifically designed for your usage.

Related Questions

What is a primer and do I need to use it?

Primer is used to ensure that the paint will stick to the surface of what you are painting. If painting rough wood, it is a good idea to prime it before painting in order to seal it.

Many companies today have primer and paint combinations that eliminate the need for separate products. You can find these all-in-one solutions in both interior and exterior options at your local hardware store. The number of coats needed may vary, so be sure to check the can for instructions.

How many coats of paint are recommended?

If you are painting a well-primed surface, indoor or outdoors, two coats should be enough. A third coat, however, can help even out the paint if you can still see brush strokes or other imperfections.

Additionally, if you are covering up a darker color of paint, you may need more coats. In this case, it may be best to prime first, since white primer can help cover the paint underneath.

Benjamin Panico

Benjamin is a freelance writer and graphic designer. He is passionate about DIY projects and finding creative ways to upcycle things headed for the landfill. Based in Oakland, CA, Benjamin enjoys playing guitar and gardening.

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