How Cold is Too Cold?

Well, it’s been a busy, fun filled year of industrial maintenance painting. The leaves are gone, grass is turning brown, and most exterior painters called it a wrap a month or two ago. Ever wonder why some painters pull the plug September 30th and others go through October or even later? Maybe they’re reckless, and just planning on redoing it when it falls off in the spring? Or the builder/owner is being pushy and insisting it get done? Well, it could be a combination of many factors; a couple of which we’ll examine here.

exterior painting cold weatherCondensation is a Key Element

If you were to pick one individual element that makes painters start thinking about interior work, it would be condensation. The relative humidity and the ambient temperature work together, such that when you get to the job in the morning, there is dew on the grass. Oftentimes, that means there is also dew on whatever the structure might be that you are painting. Sometimes you can’t even see or feel it, but it’s there. That is why most paint manufacturers specify that the substrate (surface that you’re painting) temperature must be at least 5 degrees warmer than the dew point, and rising. Generally, that means the substrate is dry, and/or drying. We use handheld laser thermometers to monitor surface temps throughout the day.

Radiant Heat Plays a Part

A common scenario… Say you pull up to the job, to keep it simple let’s just say you’re painting a metal light pole. Hop out of the truck at 7 am. Using your miscellaneous gadgetry (truck thermometer, laser thermometer, cell phone) you come to the conclusion that the air temp is 48 degrees, the dew point is 46 degrees, and the light pole itself is 44 degrees. The pole is the coldest because it is steel, and its temperature will lag behind actual ambient conditions by an hour or so. In this situation, the pole probably has heavy condensation on it, much like your windshield did when you left home. In the same way you used your defroster to clear your windshield, you’re going to let the sun clear (dry) the light pole. It might take anywhere from an hour (of sunlight) to a few hours, but eventually the radiant heat from the sun will warm the metal pole to above the dew point.

Once that happens, the condensation will start to evaporate from the pole, and in roughly an hour, the pole will appear to be bone dry, and often is dry. Now you re-check your gadgetry (9 am), and determine that the air temp has rose to 58, the dew point has rose to 50, and the steel pole itself is registering 62 degrees. Well lucky you! You’re ready to start painting! But wait, how could it be that the light pole is actually warmer than the air that surrounds it?! Something must be wrong with your thermometer right? Nope, wrong. The gadgets work just fine. The answer is, radiation. When the rays from the sun hit dense objects, they can raise the temperature higher than the air that surrounds them. This is why your body feels cooler when you’re sitting in the shade, than lounging in the sun. The actual air temperature is the same in the sun or in the shade, but the lack of radiation (radiant heat) is what makes it feel cooler in the shade. Ever felt yourself getting a good sunburn in the sun? That is the radiant heat doing its job, and it works just as well for warming up objects for painting.

If you’re painting a dark object, it works even better and can help you later into the colder season, than if you were painting over something that is a light color, such as white. During the summer, I have often seen surface temps almost double of the air temps. A good example of that is when doing corrugated metal roofs. On a nice 80 degree day, we have observed surface temps on dark roofs in excess of 140 degrees Fahrenheit. Ever seen a cat on a hot tin roof? Kinda makes sense now…

A Favorite Novolac Epoxy

Ok, back to where we were. The light pole scenario is an actual situation, that we have been through countless times. As long as your cognizant of the conditions, and follow the paint manufacturer’s instructions, it is amazing what you can accomplish with modern paint technology. One of our favorite go-to Novolac Epoxies is actually approved to go on down to ZERO degrees F. The rules regarding dew point still apply though, so careful consideration and expert knowledge is mandatory if you decide to work in those extremes. I personally did a project with that epoxy several years ago, and it was 28 F in late November when we did it. I have stopped by every fall since then, and been nothing short of impressed with how it has held up. So far, there is no appreciable difference between that project and countless others we have done during prime exterior season.

So in conclusion, when is it time to to pull the proverbial pin on exterior season? The cause is usually condensation, which effects efficiency. In the scenario I described above, there is a good chance that the crew is sitting in the truck or otherwise milling around (assuming everything else is prepped/cleaned), unproductively, while waiting “for things to warm up”. Sometimes you can get working by 9 or 10 am; some days you may have to wait until noon. Generally, you also end up having to quit earlier in the afternoon, because the evening dew will be settling in earlier as well, which doesn’t give your coating much time to dry. Therefore, it affects profitability if you can only get in 4 or 6 hours a day working productively; not to mention the fact that most tradesmen like to work a full day. That is why most contractors will switch to interior work as soon as the dew starts disrupting their work schedule.

Well, I hope you had a fun, eventful year as we did. We look forward to putting our knowledge to work for you, in the near future. Happy Trails, Bryce


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