How to Know if the Atmospheric Conditions are Right for Painting

Surface should be completely free of moisture throughout the painting process

It is critical to the success of most coating systems that the surface is completely free of moisture prior to and during paint application and curing. Condensation of water (dew) from the atmosphere on to the surface will occur, given the right conditions.

For any given set of conditions, the temperature at which condensation will occur is called the Dewpoint. As long as the surface temperature is 3°C (5°F), or more, above the Dewpoint temperature, it is generally considered safe to paint as far as risk of condensation is concerned.

How to use the chart to calculate dewpoint

  1. Measure:
    • Air temperature
    • Surface temperature
    • Relative humidity

    Use the same instrument for reading the air and surface temperature, and with an accuracy of ±0.5°C.

  2. Calculate: The temperature difference i.e. air temperature minus surface temperature.

  3. Plot and intersect: On the chart mark the temperature difference and the relative humidity.

    • If within the grey area conditions are safe to paint.
    • If above the grey area conditions are UNSAFE for painting.

If you would like to calculate this automatically use a Whirling Hygrometer or a Dew Point Meter.

Atmospheric conditions for paint application chart
Atmospheric Conditions for Painting

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