If you were to catalogue how long you spent thinking about any one topic during your life, pondering how paint dries probably ranks near the bottom. After all, the process seems pretty straightforward, and boring, that it doesn’t require much thought. Paint starts of wet, you give it some time, and it becomes dry. Done and done. Right?
Well, not so fast.
Painting engineers and house painters understand the particular nuances of what paint needs in order to dry. Understanding these concepts can help overcome the challenges inherent when trying to paint during the winter.
The Process of Paint
To start with, paint does more than just simply dry. It develops a film that changes from a viscous liquid into a strong, extremely thin solid. Even if this doesn’t necessarily sound all that remarkable, when you consider the process of how paint goes from being a thick liquid in the can to adhering seamlessly to our walls, it becomes a lot more interesting.
Each type of paint, whether alkyd, epoxy, latex, oil, or whatever, creates this film barrier in a different way. Since latex paint is most commonly used in homes, we will focus on why you may experience trouble using this type of paint during the winter.
Even though you can’t see it, latex paint is made up of a mixture of tiny plastic beads suspended in water. The beads of plastic are not water soluble, so they never mix with the water, nor do they ever bond together when in the can due to a third component of the paint called the surfactant. A soapy oil that coats each bead of plastic in the paint, the surfactant makes each bead bounce off each other without sticking.
When working with latex paint, the drying process occurs in three steps. The first step involves the water evaporating out of the paint. This in turn causes the second step. Without the presence of water to keep it hydrated, the surfactant in the paint begins to run off and evaporate from the plastic beads. Finally, without the surfactant to keep the beads from mixing, the plastic begins to blend together in the third step of the process known as coalescence. This final step is what creates such a strong bond between paint and the surface it covers.
When you apply latex paint to a cold surface, or a wet one if attempting an exterior paint job during the winter, this process gets interrupted. Because of the cold temperature, the first step of the drying process never takes place. When the water doesn’t evaporate, neither does the surfactant. Since the surfactants are heavy and applied vertically to the painting surface, gravity begins to take hold, causing the sealants to bleed together and leach out of the paint. Since the surfactants have begun to leave the paint, the plastic beads start bonding together, but since so much moisture still remains, they begin to clump together and don’t stick to the painting surface.
When trying to paint in the winter, you need to select days that offer the best possible conditions. If painting a room, especially one with exterior walls, wait until the temperature outside is over 35 degrees Fahrenheit. When the temperature outside is above freezing, you’ll have less trouble getting the paint to dry. Ideally, you’ll also wait until you get a day that has both a higher temperature and lower humidity levels.
Before you start painting, turn up the heat in room until it reaches the warmest temperature possible. The best way to do this would be to place space heaters in the room, pointed at the walls. Once the temperature of the walls has risen, begin painting. You’ll need to keep the windows closed during this process, so be sure to either wear a painters mask or take frequent breaks if the fumes begin to effect you. After you have applied paint to a wall, turn a ceiling or box fan on in the room to create air circulation. This will quicken the drying process, helping to ensure the first stage of drying occurs.
You need to keep the paint thin as you apply it to the wall, so don’t reapply paint to the brush or roller until it has run completely dry. While a thin coat will help the drying process, it will make your paint job appear a light, which may necessitate applying several coats before you finish painting the wall surface. Make sure you wait until the previous coat has completely dried before adding the next one. This will require a greater commitment, but this unfortunately is the cost of painting during the winter.
If you live in a wet, cold climate, painting the exterior of a home is almost impossible during the winter. However, if you find a day with warm weather, no moisture or humidity, you can attempt to paint the exterior of your home. Just be sure that the advanced forecast doesn’t call for any moisture for the next three days prior to beginning to paint.
A freelance writer, Timothy Lemke learned a number of tricks from the painters in Hillsboro, OR at Brian Hoge Painting.