Wednesday, September 7, 2011

Is it too cold to paint?

All the painting tips in the world wont help you if you apply paint in paint in too hot or cold weather. 


We just experienced the first cold snap here in Colorado and exterior house painting season is nearing an end. So what are safe temperature ranges to apply paint as the weather starts to get colder? That's a great question and to properly tackle this question we need to refer to the "Dew Point" chart...




















What is Dew Point?
Dew Point: The atmoshperic temperature (varying according to
pressure and humidity) below which water droplets begin to condense and dew can form.

Hoe do you use the Chart?
An example application of the chart: If the ambient air temperature is 70 degrees and the relative humidity is 70% then the dew point is 60 degrees. This temperature could result in failure.


What is the Equation for Dew Point?
If the chart is not accurate enough for your next project just use the simple and easy to use equation below:
\gamma(T,RH) = \frac {a\ T} {b+T} + \ln (RH/100)
...yeah kinda complex but here is a link for an easy to use online Dew Point Calculator

Some quick rules of thumb for applying exterior paint: 

  • no coating should be applied if the substrate is below 62 degrees
  • exterior house paint needs to dry for a minimum of eight hours in a safe Dew Point
  • 76 degrees is ideal for normal drying time
  • do not paint in hot conditions above 95 degrees
  • do not paint if humidity is at or above 90%
  • if the surface is hot to the touch do not apply coatings
  • it is not recommended to paint if the humidity is less than 20% as the film will skin over too quickly

Want to know the dew point of your region? Here is a link to the Weather Channel's Current Dew Point Map.




***This article is written as a guide and as always you want to check the back of the paint can and when in doubt always contact the manufacturer for proper guidance.***

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