Professional Tips on Cold Weather Painting
What to Do and What to Avoid
Painting during winter or any time cold weather has set in is sometimes unavoidable. Many homebuilders and remodelers try to get everything done before temperatures drop, but sometimes the timing is just not right. Cold weather generally is defined as temperatures ranging between 35 and 50 degrees Fahrenheit. If you don’t have any option other than painting in those temperatures, you still can do so if you follow some important tips.
Temperature's Impact on Paint
Understanding how low temperatures can affect paint application and how they change the drying pattern, characteristics, and performance of the paint can help you prepare for painting in the cold. Alkyd and oil paints are based on natural oils and resins that become more viscous at lower temperatures. So, when painting in cold weather, or even at freezing temperatures, some paints will become very thick or semisolid, requiring excessive thinning. However, slower evaporation rates contribute to latex paints freezing at low temperatures, requiring special additives to improve freeze/thaw resistance.
These same additives can be used for hot weather painting to make the brushing and rolling processes easier. Many of these factors also add to the mixing time necessary before applying the paint.
If using latex paint that has gone through several freeze/thaw cycles, check to see if it has become lumpy. When such consistency is observed, the paint is no longer usable and must be discarded. Latex paints are manufactured to undergo a limited number of freeze/thaw cycles, but it doesn't take long for them to reach the point of needing to be discarded. Latex-based paint freezes at the same temperature as water, while oil-based paint is more resistant and won't freeze until it reaches lower temperatures.
Cold weather slows drying time and extends recoat times. Recoat time using latex paints at 75 degrees Fahrenheit requires a period of four hours. If the temperature drops to 50 degrees, the recoat time will be extended to six hours. Painting in cold weather using alkyd paints requires even more time—in some instances more than 48 hours before recoating.
Note that direct sunlight or a lack of direct sunlight can cause surface temperatures to vary between different areas on the same structure. This obviously impacts dry times and recoat times as well.
Other issues to look out for when painting in cold weather include film cracking, poor touch-up, inadequate stain resistance, poor color uniformity, and water spotting—especially with latex paints.
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 mil to 6 mil plastic (anything between .004 inches thick and .006 inches thick) and either two-by-fours, 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 Fahrenheit. If doing this, 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.
Best Paints and Tools for Cold Weather
Many top paint manufacturers sell paints specially developed for cold weather. Most of these are rated for temperatures no colder than 35 degrees Fahrenheit. It's best to use one of these paints if your project must be completed in cold weather. Paint isn't the only concern, though. Make sure you have appropriate tools for handling such temperatures. Paints will be thicker in the colder temperatures, so also use rollers and brushes designed to handle thicker paint. Nylon and polyester brushes tend to be best for this since they are stiffer and hold thicker paints better.
Another good item to have is an infrared measurement tool. The temperature of the surface where you'll be applying the paint is just as important as the air temperature, and this tool can let you know precisely how cold that surface is.
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 warmest 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.
As well, schedule your painting for the time of day when the sun will be shining on the area where you are painting. This will help to raise the temperature in that area as well as the temperature of the surface being painted.