Every year around the beginning of Spring, people ask me, “When is it safe to start painting outside?” I wish the answer were more cut-and-dry (pun totally intended, sorry), but there are too many variables to give a definitive answer. However, here are the main factors to consider when you’re trying to determine whether or not you could safely begin your exterior painting project:
NOTE: The following list is prioritized, starting with the most vital. It’s also based on our climate here in Oregon and Washington. Although actual dates and/or months may vary from year-to-year, this list is based on the assumption that the average temperature stays above 35 at night, 45 during the day, with a relative humidity no higher than 20-30%.
1. First and foremost, figure out how long your job will take, then add 25% more time to account for the unmentionables that can, and probably will, come up. Do not include power-washing in your time projections as this should be done at least a week in advance in warmer weather, or at least 2 weeks in advance if it’s still somewhat iffy outside. If your home requires very little prep and the weather is consistently warm and dry, you may be able to paint within 3 days of power washing (but I prefer not to risk it).
2. Check your local forecast. To be safe, make sure you have dry weather projected for at least 2 days before the job and 1-2 days after. The earlier in the year, the more dry days you’ll need before and after your paint job. Also, the more preparation your home requires, the more dry days you’ll need. Lots of prep means lots of caulk, putty and primer – all of which are sealants of one kind or another and all will slow your top-coat (final coat) from drying and curing. Of course, product choices will also affect dry-time (i.e. latex versus oil and low-temp versus standard).
3. Next, make sure your siding is dry. How do you do this? Well, unfortunately, it’s not as easy as touching it to see if you get water on your hand. If the weather hasn’t been warm and dry, use a Protimeter to check your moisture levels. Quality painters should either have one or have access to one. What if you’re taking on the job yourself and don’t have a Protimeter lying around? Of course you don’t have one silly. Luckily, you can rent them from people and places by the hour and/or day. Or you could get a fairly descent entry-level Protimeter at your local big box store for under $70. Protimeters very accurately measure the moisture level of a surface and they’ll have markings right on them which let you know what percent saturation the surface is and at what percent is too wet to paint (usually higher than 15%). Make sure and check the saturation level of your siding with the Protimeter in at least 2-3 places on each side of the house, paying close attention to areas which typically accumulate the most moisture, such as window sills, underneath edges of your siding, etc.
4. Pay close attention to the weather forecast throughout your project, since it weather can change quickly (as we know well in the Pacific Northwest). There are apps available on your smartphone which could help with this immensely.
5. Don’t forget to check humidity levels, since a humid day can slow the drying process of your paints substantially.
6. One last figure to look at is the relation of Wet Bulb Temp to Dry Bulb Temp. You don’t have to learn what they mean, just make sure that they are NEVER within 5 degrees Fahrenheit of one another throughout the application phase.
Hopefully, this list will help those of you who are trying to determine if it’s safe to paint outside. Your list for your home may vary at least slightly, but feel free to use this list as an outline. When in doubt, play it safe! The last thing you want to do is paint over wet siding, since it can cause bubbles or blisters to form, and inevitably lead to premature failure of your paint-job.