Many home builders and remodelers try to get all of their painting done before the temperature drops, but sometimes the timing is just not right. For the purposes of painting, cold weather generally is defined as temperatures below 50 degrees Fahrenheit. If you don’t have any alternative to painting in those temperatures, you still can do so if you follow some expert tips.
What Cold Does to Paint
Temperatures below 50 F (typically) can have a variety of negative effects on paint and paint application. Alkyd and oil-based paints are made with oils and resins that become more viscous (thicker) at lower temperatures. This can make it very difficult to apply the paint evenly or smoothly. Water-based, or "latex," paints are made with water and thus are susceptible to freezing in cold weather. You can add freeze-resistance by mixing in a paint additive containing an antifreeze chemical.
Both alkyd/oil and water-based paints are formulated to cure within a specific temperature range and may not cure properly at temperatures below that range. The chemicals in the paint need the proper temperature to coalesce or bond together. Improper curing can lead to a number of problems, including poor coverage, blushing, peeling, bubbling, cracking, low sheen, and color inconsistency.
Is Previously Frozen Paint Usable?
Water-based paint that has gone through several freeze-thaw cycles may still be usable, but not always. If a previously frozen paint is lumpy and will not mix to a smooth consistency, it is no longer usable. This indicates that the paint has lost its ability to emulsify and is incapable of curing properly. Due to its water content, water-based paint freezes at 32 degrees F, while oil-based paint is much more resistant to freezing.
Recoating in Cold Weather
Cold weather slows the drying time of both alkyd/oil- and water-based paints. This means that recoat times are also extended. For example, at an ideal temperature of 75 degrees F, you can usually recoat after four hours. But when the temperature is about 50 degrees F, the recoat time may be extended to six hours. Painting in cold weather using alkyd or oil paints requires even more time—in some instances, more than 48 hours before recoating. To prevent problems, always follow the manufacturer's recommendations for recoat times.
Note that direct sunlight or shade can cause surface temperatures to vary between different areas on the same structure. This is another factor that impacts drying times and recoat times.
The Best Paints for Cold Weather
Many major paint manufacturers offer special paints that are formulated for cold weather. Most of these are rated for temperatures no lower than 35 degrees F. It's best to use one of these paints if your project must be completed in cold weather. A paint that's designed for lower curing temperatures is more reliable than standard paints mixed with additives for freeze-resistance or thinned for easier application.
Note that the temperature must be at or above the minimum recommended curing temperature for the entire curing process, not just during application. If you add a fresh coat of paint in 45-degree weather, but then the weather turns colder an hour later, the paint may not cure properly even though it will eventually dry.
Because paints are thicker in lower temperatures, it's best to use relatively stiff brushes with nylon, polyester, or Chinex bristles, all of which tend to work well with thicker paint.
Surface Temperature Matters Most
The minimum application temperature specified on your paint can relate not only to the air temperature but also the temperature of the surface to be painted. Often, the wall or ceiling surface is colder than the air, especially if there is wind. If the air is 55 degrees F, but the wall surface you're painting is only 40 degrees F, it's as though you're painting in 40-degree weather.
Painting professionals use infrared thermometers to take the guesswork out of painting in questionable temperatures. These emit an infrared beam to measure the surface temperature of anything you point it at. Inexpensive versions can cost well under $50 and are a worthwhile investment for sizable painting jobs.
Tracking the Weather and the Sun
Before beginning work on your project, check local forecasts and find a stretch of a few days when temperatures will be their highest and the sun will be out. You'll need to have a few days in a row when temperatures don't drop below the minimum for the paint you are using because you also need to factor in drying time for multiple coats.
Plan each coat for times when the sun will be shining on the area you are painting. Direct sunlight quickly raises the surface temperature of most building materials. In hot weather, sunlight should be avoided, but in cold seasons it's preferable to paint in direct sun.
Building a Bubble
One way around cold temperatures is to build a bubble over the area where you wish to paint. You can do this using 4- to 6-mil plastic sheeting supported by a framework of 2x4s, zip poles, or scaffolding. Completely enclose the area where you want to paint, and use a space heater to raise the temperature to between 70 and 80 degrees F.
Keep in mind that you need to maintain the temperature in the bubble throughout the drying time. It's also important to be safe and make sure the area is properly ventilated and not left unattended when a space heater is running.
Alkyd- or oil-based paint fumes are flammable. Do not use an open-flame space heater if working with oil based paint in a constructed bubble.