Should You Paint Inside if It’s Humid Out? Here's What the Experts Say

When it comes to home renovations, the time of year and associated weather will dictate whether you can accomplish your goals. Digging fence posts in the winter or replacing a roof in the rain are immediate passes; painting in the summer is more of a gray area.

Learn how the outside temperature affects your interior paint job, and how you can avoid these impacts.

How Temperature Affects Paint

You might not think interior paint projects would be on the list of upgrades to avoid in warmer weather, but think again. Humid temperatures affect the quality of your project—here's how.

Drying Time

“High humidity can slow down the drying time by a lot, and in some conditions, this can affect the actual quality of the paint cure,” says Brandon Walker, a construction manager with ASAP Restoration LLC. “High humidity can also play a role in causing an uneven finish. If sections of the paint are done at different times within a day, this slight variation in humidity levels between hour one and hour four can make a difference in the quality of the finish from the start of the project to the end.” 

And while it’s possible to paint when it’s humid out, it’s far from ideal. 

“High humidity will slow the drying process of the paint. This can cause a longer re-coat time, and potentially cause the paint to ‘run’ down in areas that were applied too heavily,” says Dennis Fiorilli, director of product excellence at Sherwin-Williams. “This can be fixed, but it does create more prep before starting a second coat.

Adhering to Walls

“Adhesion is critical for paint, and if the humidity is high enough, this can reduce or eliminate the adhesion capacity of the paint you are using,” Walker says. “Additional coats of paint may also be harder to apply if the humidity level is too high, again because of the adhesion factor that prevents drying.”

Humid conditions are not ideal if you're on a time constraint and need your walls painted quickly. Avoid painting with this type of weather if possible; there are also ways to mitigate the humidity, which we outline below.

Mold and Mildew

Aside from application, you could run into other major problems should you paint when it’s too humid outside. 

“Mildew and mold can also take root more easily in high humidity environments in general, but if you add paint into the equation, this can mean the spores will be embedded inside the paint layer, and this can ruin a paint job completely,” Walker cautions. 

Paint Quality

You might think your paint job went off without a hitch, but problems with high humidity can develop over time as well. 

“High humidity can cause cracking, blistering, flaking, stripping and peeling of paint in some areas or over the entire paint job depending on the specifics of the conditions and the kind of paint used,” Walker says. “Additionally, paint that is applied in high humidity conditions can also cause leaching of colors or chemicals applied below the paint and primer layer. This can lead to discoloration in splotchy sections.”

This is not just true with a fresh paint job, either. High humidity can impact even an older coat of paint with repeated exposure. 

“Long-term high humidity can lead to peeling and mildew issues,” Fiorilli says. “Think about a bathroom that does not have an exhaust fan. Proper airflow and temperature control will help mitigate the issues.”

Choosing the Right Paint

Just because it’s humid outside doesn’t mean you can’t paint; choosing the right paint to use can help. 

“It’s really the finish of the paint that can help in high humidity conditions the most,” Walker says. “A flat paint will be the worst option in these scenarios because it absorbs water droplets and vapor. This is why high gloss, semi-gloss, and satin paints are the best options when it comes to old prevention and adhesion factors for high humidity environments.” 

You can also look for paints designed to limit mold and mildew growth. Walker notes that these tend to be more costly, but in humid-prone environments, it may be the best option. Whichever you choose, make sure to follow the manufacturer's instructions regarding ideal temperature and humidity conditions. And before you paint, consider using a moisture meter to measure indoor humidity and water vapor conditions. 

“These are very affordable and can save you a lot of frustration by providing accurate information about the conditions you are considering painting in,” Walker says. “Many models are under $30 and can tell you everything you need to know before committing to the paint job.”

A simple thermometer is also smart to have on hand—Fiorilli says the ideal temperature is 77°F at 50% relative humidity.

Eliminating Humidity

Before you begin painting, try to eliminate the humidity in the room. Fiorilli suggests starting this process the day before to ensure the room is at a stable temperature before painting. After the final coat, keep the room in the same controlled environment for at least 24 hours so that proper drying can occur.

If your home is equipped with central air conditioning, you can use it to maintain temperatures as well. Just be careful that the room you’re working in doesn’t blow cold air in a way that kicks up dust and other particles that can stick to wet paint. 

“It’s also best to keep this area free of water vapor during the duration of the curing process for the paint and not just while it is drying the first day,” Walker says. “This will ensure that it cures properly and you get a good finish with quality adhesion.”

Using a Dehumidifier

In many cases, you might be better off using a dehumidifier in the room where you’re focusing on taking moisture out of the air. 

“It may cost a bit more to scrub the air for moisture by keeping some machines running until the paint cures, but it will vastly improve the quality of the finish and paint job as a whole,” Walker says.

Fiorilli also suggests checking the walls themselves for moisture. “If there is a lot of humidity, the walls tend to have moisture build up and will feel wet—this needs to be avoided,” he says. 

Ultimately, if conditions seem less than ideal, resist the urge to forge ahead with your paint project. 

“Simply wait,” Walker says. “If the humidity is too high, then it will cause more problems than simply waiting to paint ever could. In the same way that you wouldn’t build a roof in the rain, you shouldn’t paint when it’s that wet outside either. It’s just a recipe for disaster.”

Source: Kristine Gil, BHG.com