How Dew Point Affects Surface Coating Preparation for Tanks

A successful, lasting surface coating application requires the monitoring and control of specific ambient conditions, including relative humidity, air temperature, surface temperature and dew point. A lack of environmental control may result in oxidation on a surface’s substrate, as well as project delays, productivity losses and budgetary problems. When you have a better understanding regarding dew point and its role, you’ll gain better control over a project’s environmental conditions.

What is Dew Point?

Dew point refers to the temperature at which water vapor saturates the air. When air reaches a particular dew point temperature and pressure, the water vapor in the air coincides with liquid water, so it condenses at the same rate that liquid water evaporates.

Meteorologists use dew points to describe how much moisture is in the air—the temperature that air must cool to in order to reach saturation if moisture content and air pressure are constant. For example, if a meteorologist states that the dew point temperature is 48°F, water will condense on a solid surface when its temperature falls to 48° or below. This is why condensation forms on a cool glass of water on a hot summer day. The glass’ surface temperature is below the dew point temperature. When water condenses on solid particles in the atmosphere, such as salts or dust, fog and clouds form.

Dew point is related to relative humidity but is not the same. Relative humidity refers to the ratio of water vapor’s pressure and saturation in the air at a specific temperature. Scientists measure relative humidity by examining how close the air temperature is to the dew point temperature. The closer the temperature values are, the higher the humidity levels. Conversely, humidity levels are lower when the temperature values are far apart.

How Dew Point Relates to Surface Coating Environmental Control

There are several environmental factors to consider during the surface coating process. Among the most important are relative humidity, dew point, air temperature, and a surface’s temperature. When you work in an unprotected environment, you might rely on weather reports to determine if the surface in question is at risk of developing condensation. Problems tend to occur when an object’s surface temperature achieves the dew point temperature. This is more likely to happen at night when surfaces radiate the heat that they absorbed during the day. When a substrate’s surface reaches the dew point temperature, the resulting condensation puts it at risk of oxidation or flash rust. If the surface already has a fresh coating, the coating might not dry or cure properly.

In general, it is best to avoid applying coating materials to a surface whose temperature is within 5°F of the dew point temperature. During the surface preparation and coating process, the surface temperature should be 5°F or more above the dew point temperature. Refer to the manufacturer’s specifications to learn which relative humidity levels, temperatures, and dew points ensure the success of a surface coating application.

Proactive contractors use temporary humidity control equipment from Polygon that allows them to set relative humidity levels and temperatures to avoid the risk of dew forming on a substrate or fresh coats of a protective material’s application. Professionals who use these solutions experience cost reductions and time savings of up to 35 percent, improved inter-coat adhesion, and coating life increases of up to a factor of 2. Temporary humidity control also allows contractors to work throughout the year and provide optimal conditions for workers. Contact Polygon today to start experiencing the benefits yourself. 

[Photo from Andrew Malone via CC License 2.0]