Water-based exterior paint requires certain conditions to cure properly. And if it doesn’t, you might be repainting your home’s exterior sooner than you planned.
“It should be at least 50° F when applying the paint and shouldn’t drop below 32° F at night for several days after,” says Rico de Paz, who oversees Consumer Reports’ paint tests.
Paint needs several days to cure, and as the temperature dips, dew can form on surfaces and cause the water in the paint to evaporate too slowly. Even if it’s warm during the day, the paint won’t form a good film if temperatures drop too low at night.
That affects how the paint holds up over time, including how well it resists cracking. Colder temperatures and moisture on the surface can also result in staining or mildew.
Some manufacturers now claim that certain paints will cure in temperatures as low as 35° F.
But what about an upper limit? For summer days—say, when temperatures hit 90° F—there’s no hard rule about how hot is too hot outside. But you’ll want to pay attention to the surface temperature of the exterior walls of your house.
“If you can’t keep the palm of your hand on the exterior wall of your house for more than a few seconds, it’s too hot to paint,” de Paz says.
Check the label on the paint can for any instructions on the ideal temperature range, and follow de Paz’s tips, below, for nailing the job.
Prep Before You Paint
- Protect other surfaces. Cover plantings, air conditioner(s), and exhaust vents with drop cloths. Tie back shrubs and tree limbs.
- Scrub, then patch. Dirt, mildew, and chalky old paint prevent fresh paint from adhering properly. If your house was built before 1978, there might be lead paint below the surface.
- Remove mildew. Mix a solution of chlorine bleach and water, or use a commercial cleaner. Wearing gloves, a mask, and eye protection, scrub the mildew away. Scrape out rotted areas and fill them with wood filler, then sand smooth. Allow to dry for several days before painting.
- Caulk and prime. Scrape away dried and cracked caulk around windows, doors, and trim. Apply fresh acrylic caulk where needed. Prime bare wood using the primer recommended by the paint manufacturer, or skip priming by using a high-performing self-priming paint.
- Replace cracked or rotted boards. Water could still seep in if you merely fill and repair cracked or split boards.
Lab-Tested for Your Home’s Exterior
To determine a paint’s durability, we apply two coats to pine boards. Then we mount the boards on angled racks on the roof of our headquarters in Yonkers, N.Y., to see how well the paint withstands the elements. Then we wait.
Because the boards are angled, and not placed vertically as they would be on your house, they’re more exposed to light and weather. Each year of testing is equivalent to about three years on vertical surfaces. Three years later, our results give you an idea of how the paint will look after nine years. We also test for mildew resistance by placing painted panels on vertical racks in a shady area of our HQ’s campus.