Summer and early Fall is the time to work outdoors–it’s warm and there are plenty of daylight hours to finish a big job like painting an exterior. But painting outside in warm weather has its own challenges and this summer it’s just been too hot in many parts of the country. We’ve put together a few tips to ensure you can take full advantage of the weather and still get good results that will stand the test of time. Any quality paint job will require proper preparation prior to painting. This step is the same no matter what the weather but on hot and humid day it just makes the task seem a lot harder.
In the heat of summer, add to those basic rules a big “weather permitting” caveat. That’s because the temperature and humidity can play a major part in the project’s outcome, so plan what time of day you work and keep a close eye on the weather forecast:
1. Take the time to caulk open joints properly. Around windows, joints less than ¼-inch wide should be caulked. In summer that’s especially important because heat and humidity will expand wood, shrinking joints as tight as they’ll be all year. Use a siliconized acrylic or a urethane acrylic paintable caulk on those gaps. Both these caulks expand and contract, so that in winter, when the joints open up a bit, they’ll still be fairly tight.
2. Start early to beat the heat, but not too early. Even in summer, morning dew can be an enemy and interfere with the paint’s adhesion and drying times. The surface should be dry to the touch.
For the same reason, don’t rush to apply a lot of paint at the end of the day. It may be tempting to finish that section before it gets dark, but stop well in advance of dusk so dew doesn’t form on freshly painted areas. Moisture on wet paint can leave the finish uneven or possibly streaked.
3. Avoid working in direct sunlight. The maximum recommended surface temperature at application is 90 degrees. In direct sun, the surface temperature of a substrate could be 120 degrees or more. That kind of temperature can result in visible lap marks—because the heat will hinder your ability to maintain a wet edge.
Rule of thumb is that if the surface too hot to keep your hand on comfortably, it’s too hot to paint. If you want to be absolutely sure the surface temperature is good, get a basic infrared thermometer at a hardware store, and fire it at the wall to take a heat reading. Using Extender 518 will slow the drying rate of latex paint, enabling you to keep a wet edge and reducing the risk of creating lap marks in warmer weather.
4. Find the shade. Always try to work on a dry, shady side of the house so the paint doesn’t dry too fast and has time to cure properly. In the mornings, when the sun is rising in the eastern sky, work on the west-facing side of the house; paint the eastern face in the afternoon. Watch the way the sun moves across the northern and southern faces of your house, and plan to hit those walls when they will be in the shade the longest. Start with the siding, then do the trim.
5. Wind down in the afternoon. Don’t put on a complete new coat late in the day. (Dew, remember?) In ideal conditions, Water based paints are dry to the touch in 1 hour and ready to recoat in 4 hours–in summer, a morning coat applied from 8 to 10 am will be ready to recoat in early afternoon. The end of the afternoon should be spent touching up and preparing the site and equipment for overnight storage.
6. Watch the humidity. In high humidity, the air is saturated with water. So, with water-based paints it takes longer to dry because the water cannot evaporate out of the paint film. Sure, in ideal conditions the paint can be ready to recoat in only 4 hours, but that’s at a relative humidity of 50 percent–an average early summer day in most parts of the country. Be patient on a muggy day–if an edge begins to dry and you see that you missed a spot, wait until the paint is completely dry before touching up that area.
7. Watch the forecast. Always look ahead and check the overnight weather. Stop if there’s a possibility of rain so the paint has a chance to dry fully.
8. The most ideal time to paint is in the shade when the air and surface temperature is about 77° F and the relative humidity is under 50%. Unfortunately, those days are few and far between. But use that as a guideline for all you exterior painting and staining projects. As you move away from those numbers, the project will be tougher to complete and you will not get the maximum life expectancy from the paint job.
Source: Ask the Paint Gurus