You have some leftover paint in the perfect color for one of your outdoor projects. But, you’re wondering, can you use interior paint outside?
While you technically can use interior paint outside, you probably shouldn’t.
If you use interior paint outdoors, it will peel and crack over time – it’s not weather resistant and doesn’t have the necessary additives to stand up to mildew.
Here’s what else you should know.
The Difference Between Interior and Exterior Paint
All paint contains four main parts: a base, pigment, additives, and a binder. The composition of paint is what determines its uses.
Interior Paint Overview
Most interior paints are water-based, with latex paint being the most common. (Although, you still can find some oil-based interior paints.)
Manufacturers formulate interior paint to stand up to everyday wear like furniture rubbing against it, pets, and kids. It also dries fast and has a lower VOC (volatile organic compounds) formulation than exterior paint.
The lower VOCs mean it doesn’t put off dangerous chemicals hazardous to your health.
Interior paint has rigid resins, making it easy to clean up. However, it doesn’t have additives that make it weather resistant.
As a result, it cannot withstand UV exposure, rain, snow, or extreme temperature changes.
Exterior Paint Overview
Like interior paint, you can find exterior paint in oil or water-based formulas.
The most significant difference between the two is that exterior paint has special additives that enable it to hold up to sun, snow, rain, and more. In addition, the resins in exterior paint are much more flexible, allowing it to withstand temperature fluctuations.
Exterior paint is also much thicker for better adhesion to outdoor surfaces. But, because of its thickness, it has a longer dry time.
Exterior paint is treated with mildewcide and fungicides so that it doesn’t develop mildew and mold from moisture exposure.
What Will Happen If You Use Interior Paint Outside?
In most instances, you should not use interior paint for outdoor DIY projects. Interior paint doesn’t stand up to the elements.
It might not even properly adhere.
Interior paint is much thinner than exterior paint, taking many more coats of paint to achieve even coverage.
And since interior paint doesn’t have the formulation to dry in outdoor conditions, it might dry gunky or unevenly, depending on the humidity levels.
If you use interior paint outside, the weather will adversely affect your paint job over time, causing the paint to fade, flake, or peel. It may also develop mildew since it doesn’t have the necessary additives to withstand moisture.
What to Do If You Accidentally Used Interior Paint Outside?
Not all is lost if you mistakenly painted an exterior surface with interior paint. You have a couple of options:
Let nature take its course – Interior paint doesn’t last long outdoors, especially if you live in an area with a harsh climate. If you don’t want to mess with it, you can always leave it be for now and repaint it when it starts chipping away.
Repaint with exterior paint– You can go over the painted surface with exterior paint to protect it. Just make sure the product you choose will go over the interior paint without a problem. If not, you’ll likely need to prime first.
Don’t use your interior paint outdoors. It doesn’t have the mildewcide or other additives that make it weather resistant.
If you use interior paint for outdoor use, you’ll be disappointed when it develops mildew or starts peeling within a couple of years.
Instead, make sure you get outdoor paint for your exterior projects. While you might think all paints are the same, they are not.
Formulations matter, and you need to use the correct type of paint for your project.