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Humidity and temperature are crucial variables that can determine the success or failure of a project when blasting and coating a steel surface. When you are blasting, it is important to control the humidity to minimize the risk of flash rust before the coating is applied. The greatest chance for success starts with specifying the proper environment to prevent flash rusting or other conditions that may cause a coating failure. All coating manufacturers have specifications that require precise relative humidity and temperature levels during the application of the coating. If the coating is done outside of the specified parameters, a failure will likely occur.
The key figures you need when specifying the environmental conditions to prevent flash rusting are relative humidity, dew point, air changes and temperature. You need to determine the relative humidity required to slow the corrosion process to a point that will keep the steel free of rust until the coating is applied. Relative humidity should be specified using the dew point spread requirements from the ambient dew point inside the space and the steel temperature.
Temperature control is also a factor that needs to be addressed in a specification. The coating manufacturers will have a minimum temperature at the surface requirement for the coating to cure in their specification. These temperatures are extremely important to establish and maintain while the coating cures without compromising the coating’s adhesion to the surface.