Why Dew Point Matters

Dew point is the temperature at which moisture can condense from the air. If a substrate is too close to dew point, an invisible moisture film may interfere with adhesion or contaminate freshly prepared steel.

Measure the Surface

Steel in sun, shade, wind or enclosed spaces can differ substantially from ambient air. Readings should include air temperature, relative humidity, calculated dew point and substrate temperature at representative work locations.

Follow the Approved Limits

Many specifications require the surface to remain a stated margin above dew point, but the exact limit must come from the approved specification and current product data sheet. Product-specific temperature and humidity limits also apply.

Conditions Change During the Shift

Morning warm-up, afternoon storms, ventilation changes and night cooling can move conditions outside the application window. Monitoring should continue through surface preparation, application and initial cure at the frequency required by the inspection plan.

Enclosures and Ventilation

Containment can improve control but may trap moisture, solvent vapor or heat. Ventilation, dehumidification and heating must be planned for the coating system and work environment.

Document the Decision

A useful environmental log records time, location, instrument, readings, work activity and any stop/restart decision. Instruments should be maintained and verified under the project quality plan.