Having separate types of paint for indoor versus outdoor use may sound like a marketing ploy to get us to buy more paint—reminiscent of when advertisers a century ago tried to convince women to switch from a single all-purpose skin cream to using separate products for day and night. However, in this case, there are key differences between the paints. And though it’s technically possible to use exterior paint indoors, here’s why that’s a bad idea.
Why you shouldn’t use exterior paint indoors
We love reusing stuff that we already have on hand to avoid buying something new, but for multiple health- and performance-related reasons, that doesn’t apply to using exterior paint on indoor projects. Here’s why:
It’s a health risk
Most paints designed for indoor use are water-based, and are formulated to have minimal fumes, wash off your skin easily, and be generally safe to use. Exterior paints tend to be oil- or solvent-based, and formulated to withstand serious temperature fluctuations, along with moisture, precipitation, and direct sunlight.
The ingredients that make that kind of durability possible may irritate a person’s skin or eyes, but the fumes from the paint pose the biggest threat to health. That’s because these exterior paints often contain volatile organic compounds or VOCs, which are released into the air as they dry and cure—or even longer if you’re using exterior acrylic latex paint, which continues to off-gas after it dries.
According to Poison Control and the U.S. Environmental Protection Agency (EPA), when someone inhales fumes containing common VOCs—like benzene, formaldehyde, toluene, xylene, ethanol, and acetone—it can cause:
- Headaches
- Dizziness
- Nausea
- Eye, nose, and throat irritation
- Loss of coordination
- Damage to liver, kidneys, and central nervous system
The VOCs are less of a problem when exterior paint is used outdoors by someone wearing a face mask and other PPE. But even with all the windows and doors of a house open, there still wouldn’t be sufficient ventilation for using exterior paint indoors.
Exterior paint doesn’t perform as well indoors
Health risks aside, exterior paint isn’t a good choice for indoor projects for other reasons, including:
It needs sunlight to cure properly
While exterior paint will eventually cure indoors, it will take much longer than interior paint, leaving your walls vulnerable to scratches, scrapes, scuffs, and other indentations for an extended period.
It doesn’t stand up to indoor messes
Exterior paint may be weather resistant, but interior paint was formulated to withstand everyday wear and tear from kids, pets, the vacuum, indoor humidity from cooking and showering, scuffs, and scratches. It’s also more resistant to grease and oil, and easier to clean.
It’s not great on drywall
While exterior paints are perfect for vinyl, stucco, wood, and other home construction materials, they don’t bind to drywall very well.