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Wednesday, October 13, 2010


Advice from the Pros:

Cool Weather Painting

Fall is a great time to finish up outdoor projects, but a lot of homeowners wonder if it's safe to paint in cooler conditions. The short answer is yes...but you'll need to pay closer attention to weather conditions than during the longer days of summer. This is because most paints are formulated to cure best when temperatures are around 70 to 77 degrees F and relative humidity is around 50%. The more temperature and humidity deviate from those optimal conditions, the riskier it is to paint. Here are some quick guidelines to help you determine whether you should pick up a brush, or move on to other projects on your To-Do list.

exterior painting in cool weather

Temperature. In summer, a good rule of thumb is to plan your painting so that you're always working in the shade, so that surface temperatures don't get too hot. But in cooler months, painting in direct sun is actually a good idea, because this will help boost surface temperatures up into the safe range--around 70-degrees--even when air temperatures are chillier. In general, paints should be applied only when both surface and air temperatures are above 40 degrees; primers generally need temperatures above 50 degrees to dry properly.

Not only should temperatures be above 40 degrees when the paint is applied, but they should remain that way for at least 2 or 3 hours for paint to dry properly. Usually the best window for painting in cooler conditions is between 10 am to 3 pm, but it can be considerably shorter in marginal conditions. Dew is another reason to avoid an early morning start. Watch for signs of moisture on the lawn and make sure it's fully evaporated from the work area before starting.

It's also important that air temperatures don't drop below freezing the first night after paint has been applied, since curing paint can still contain moisture that will crystallize in sub-freezing temperatures, instead of evaporating out into the atmosphere as it's designed to do. (If temperatures do drop, you won't see a problem until the following spring: Moisture will remain hidden in the wood siding over the winter, then migrate out into the paint under a warm spring sun and form blisters.)

Humidity. Relative humidity is harder to measure than temperature, but it plays an equally important role in how well paint cures. The ideal is 50% relative humidity, but curing times are significantly affected when humidity levels exceed 70%. In high-humidity situations, you could see what is called surfactant leaching, brown or white discoloration on the surface of the paint. Minor surfactant leaching can be rinsed off with a hose or can be left to wash away with normal weathering.

Low relative humidity can also be a problem, because the paint surface may dry too quickly and lead to blistering later on. But this is less common in cooler temperatures; more often, the problem is too much wind, which can also dry paint too quickly and deposit dust and other particles on the surface.

Finally, it's probably a good idea to avoid pressure-washing in the fall, since it will take a long time for your siding to dry out. Pros use moisture meters to determine the moisture content of the substrate that they're painting, to avoid blistering later on; a safe level for wood shingles and clapboards is 12% moisture content.

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Comments

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HHH Yes, the design of national policy is important, how our economic development plans for the next five years, how the implementation, how to make our economy even faster. Are designed to advance our focus to invest money in what ways it should be carefully arranged.

For me, fall is also the best time to paint sidings, especially during September and October. Even though I paint my sidings at lunchtime or in the early afternoon, the heat is bearable enough to let me work comfortably.

Environmental factors that influence drying times of acrylic paint films are temperature, humidity and airflow. In general, a latex paint coating will be dry to the touch in a couple of hours, ready for recoating in 24 and cured for the most part in 7-10 days.

A full cure might take up to 3 to 4 weeks.

Blocking occurs if two painted surfaces stick when pressed together, such as a door sticking to the jamb or as in your situation, the jamb on a casement window. The higher the gloss level, the more resistant the finish will be to blocking. You may experience some blocking if you decide to use an acrylic paint finish such as our 514 Natura Acrylic Semi-Gloss Zero VOC Enamel. Give the paint at least 3-4 days before closing the window—if possible.

If the surfaces were well prepared and the paint was applied according to the directions found on the paint can label, blocking should not be an issue provided the two sticking surfaces are allowed the time to dry before being shut tight.

To alleviate the paint from sticking, try dusting the surface with some talc (baby powder) or another suggestion is to rub a small amount of paraffin wax directly on jamb as well as the edge of the window where it meets the jamb.

I hope these suggestions help!

Can BM paints that have been allowed to freeze in the garage be used, and if so, what measures do I take? Both latex and alkyd, gloss and otherwise. Thank you.

We recently had our casement windows painted on the inside of our home. We used a Natura semigloss paint. Ever since then, the trim around the windows have been sticking to the frame (also painted) when we open them. They make a loud cracking sound when opening and in some places, the wood from the frame has actually chipped off and stuck to the trim around the window. There was some paint on the rubber weatherproofing strip on both the trim and frame, but we removed that.
We would really appreciate any advice you could provide regarding this situation.
Thank you!

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