The dew point is the temperature at which moisture in the air condenses into water. If a surface is colder than the dew point, a thin film of water forms on it. Coatings applied over that moisture can bond poorly or blush. Installers commonly keep the surface at least 5°F above the dew point.
Why Dew Point Matters for an Epoxy Floor
Weather forecasters define dew point as the temperature air has to cool to before it’s fully saturated. Below that, water comes out of the air as liquid. You’ve seen it on a cold glass of iced tea on a muggy day.
A concrete slab can act like that glass. Garage and basement floors sit on cool ground, so they often run colder than the air above them. On a humid day, the slab can drop below the dew point and pick up a film of moisture too thin to see. A coating rolled over that film may not grip well, and it can turn cloudy or develop a waxy surface known as amine blush.
How Installers Check the Dew Point
A careful installer checks air temperature, humidity, and the slab’s surface temperature, then works out the dew point. Coating makers set a gap; one floor system, for example, calls for concrete at least 50°F and more than 5°F above the dew point.
If the numbers are too close, the crew may add heat or a dehumidifier, or wait. See also cure temperature.
Dew Point FAQ
Can you epoxy a garage floor in high humidity?
Sometimes, as long as the slab surface stays warmer than the dew point by the margin the product requires. Humid days with a cold slab are the risky ones.
What happens if moisture gets under an epoxy floor?
Moisture trapped under epoxy can weaken the bond, leading to bubbles, cloudy spots, or peeling. That’s why installers test both the slab’s moisture and the air conditions before coating.