Over the past few years, a number of paint companies have developed latex paints that will cure at temperatures below 50º F, thereby allowing painters to extend their exterior painting season. The purpose of this post is to provide a better understanding of how application conditions can impact the overall appearance and performance of an exterior paint job and what you can do to mitigate negative effects.
Latex paint consists of dispersed pigment and resin, along with some additives and liquid, which is mainly water. When the paint is still in its liquid state, the particles of pigment and resin are evenly distributed and spaced out. After application, the water begins to evaporate, and the particles of pigment and resin come closer together. As the remaining liquid evaporates, the resin particles gradually become more densely packed, causing them to fuse and bind the pigment into a continuous film. This process is, called coalescence.
The mechanism of latex paint film formation has some limitations. Because the resin particles are thermoplastic (tending to get softer at higher temperature, and vice-versa), lower temperatures harden the latex particles preventing proper coalescence. In severe cases, this may result in the film actually cracking. In milder cases, the film may exhibit poor touch-up, holdout, paint color uniformity or uneven sheen.
Cold Weather Exterior Painting Precautionary Measures
You can reduce the chances of experiencing these effects by incorporating the following tips into your painting project.
- Check the weather forecast. Determine the weather pattern for the days you are going to paint. Cold-weather paints may take up to two days to dry, and the minimum temperature must be maintained during this time period. If the temperature is going to dip below the minimum mark during the drying phase, painting must be suspended until stable temperatures can be guaranteed.
- Pay special attention to the substrate. Both air and substrate temperatures should be above the specified minimums.
- Work midday. Focus on prep work in the early morning and late afternoon, and apply paint between 10 a.m. and 2 p.m. to allow surfaces to warm up and to allow time for curing before dew falls.
- Follow the sun. With hot weather exterior painting, the rule is don’t paint in the sun and follow the shade around the house. But in cold weather, it’s the opposite. Follow the sun around the house as you work. Stop work around mid-afternoon, or when the temperature starts dropping.
By knowing more about how paint binds to surfaces and using these tips, you can still successfully pull off a perfect paint job in cold weather conditions.