Plenty of exterior coats go on in perfect-looking weather and still fail. The culprit usually isn’t the high temperature — it’s the dew point, and how close the surface gets to it as the day cools.
The gap is the dry time
Paint cures while the surface stays comfortably above the dew point. As evening approaches and the temperature falls toward the dew point, drying slows and condensation risk climbs. A wide spread between air temp and dew point means fast, clean curing; a narrow spread means trouble, even at 75°.
What we track for a coat
- Dew point and the temperature spread through the back half of the day
- Surface temperature versus the product’s minimum
- Time to evening — will the coat set before the spread closes?
- Overnight moisture — dew settling on a not-quite-cured surface
Counting backward from sundown
The real question is whether there’s enough dry time left before the spread tightens at dusk. DecideWeather watches the dew-point spread across the day and turns it into a Go / Caution / Stop recommendation for painting — so you start a coat only when it has room to cure.