Dew point is the temperature at which moisture in the air condenses into liquid water on a surface, and it is a critical measurement for timing coating applications to avoid trapped moisture.
Understanding Dew Point in Coating Applications
Dew point is the temperature at which the air holds all the moisture it can and starts condensing it onto a surface, similar to how a cold drink sweats on a warm day. For coating contractors, this matters because concrete can be cooler than the surrounding air, especially early in the morning or in a climate-controlled building, and condensation on that cooler surface can happen without any visible sign of it.
The 5-Degree Rule
A widely used rule of thumb in the industry is that the substrate temperature should stay at least 5 degrees Fahrenheit above the dew point throughout the application and cure. If the slab is too close to or below the dew point, invisible moisture can form on the surface right as the coating is applied, leading to poor adhesion, blushing, or a hazy finish that shows up after the fact.
How to Check Dew Point on a Job Site
Most contractors use a hygrometer or a combination temperature and humidity meter to pull the readings needed to calculate dew point, and many job site tools calculate it automatically once air temperature and relative humidity are entered. Checking this first thing in the morning, and again if weather conditions shift during the day, is standard practice on any exterior job and on interior jobs without full climate control.
When Dew Point Conditions Get Risky
Early morning starts, humid climates, and buildings without HVAC running during the job are the most common situations where dew point becomes a problem. Delaying the start of a coat by even an hour or two, until the substrate temperature has moved further away from the dew point, is often all it takes to avoid a failed application.
