Two of the most important factors affecting how paint dries are temperature and humidity. Avoiding adverse environmental extremes can help you avoid painting problems.
Several factors affect how quickly paint and other coatings dry. These factors include paint formulation and coating thickness along with temperature and humidity.
The rule of thumb is that if you are painting with an oil-based paint, the ambient temperature should be above 45°F or 7°C. Latex and acrylic paints typically require higher temperatures above 50°F or 10°C. Some paints, however, are formulated to dry at lower temperatures, even as low as 35°F or 2°C.
Because application temperatures will vary from one manufacturer to another, and from one product series to another, you should read and follow the directions of manufacturer. In selecting paint for a project, do your homework and study the specs carefully, so you can pick the right paint for the job and avoid painting problems.
How Temperature Affects Drying
Here’s why temperature is so important. As ambient temperature lowers, the paint thickens. The thicker the coating is, the longer it takes for the greater volume of paint to oxidize in the case of oil-based paints. In addition, when a coating is thicker, it extends the time it takes for the solvent to evaporate.
The slower drying times and heavier coating can result in paint problems. The longer it takes for the paint to dry, the more time the paint has to sag or run. Thicker paint coatings are also more prone to wrinkling.
Lower temperatures can also inhibit the paint from properly adhering to the substrate. Of course, you should never paint with a water-based paint in freezing temperatures because water freezes. When that happens the paint is ruined.
The optimum temperature for painting is between 60° F and 80° F or 16° C and 26° C. The warmer the ambient temperature is the faster paint dries. Excessively hot weather, however, can cause the paint to dry too fast. When the temperature is hot, the surface of the paint can skin over before the lower layers have a chance to dry. The result can be surface imperfections, such as bumps or wrinkling. What’s more, when air temperature is over 100° F or 38° C, the paint can blister or bubble.
How Humidity Affects Drying.
Relative humidity is also a key factor affecting how paint dries. It affects drying not only of acrylic and latex paints, but also drying of oil-based paint. When humidity is high, the paint is exposed to a greater amount of water vapor.
With more moisture in the air, it takes longer for the water in an acrylic or latex paint to evaporate. Whereas oil-based paints cure through oxidation, water based paints dry through evaporation.
High humidity can also cause a problem, when you paint a wood surface. The wood can absorb the moisture in the air. The water absorbed can compromise the adhesion of the paint to the surface, resulting in peeling or bubbling paint.
When you combine low temperatures and high humidity in painting outdoor projects, condensation on the surface of the paint often occurs. This condensation can result in marring of the paint finish.