Question 1

What is dew point in coating application?

Accepted Answer

Dew point is the temperature at which moisture in the air condenses onto a surface. If a concrete slab sits at or near dew point, an invisible film of moisture forms on it, and any coating applied bonds to that moisture instead of the concrete, leading to blistering and delamination.

Question 2

How much above dew point must a slab be before coating?

Accepted Answer

Standard coating practice, following ISO 8502-4, requires the substrate to be at least 3 degrees Celsius above dew point during application and until the coating has cured sufficiently. A smaller margin risks condensation forming mid-application.

Question 3

Why does the slab temperature matter more than air temperature?

Accepted Answer

Concrete holds thermal mass and typically runs cooler than the surrounding air, often by 2 to 4 degrees Celsius indoors and more after cold nights. Because condensation forms on the coldest surface, the slab reading decides the outcome even when air conditions look acceptable.

Question 4

When can you not apply epoxy during the Indian monsoon?

Accepted Answer

During monsoon months, ambient humidity often stays above 80 percent, pushing dew point close to slab temperature. Early mornings and evenings commonly fail the 3 degree margin, particularly in coastal zones, leaving only the warmest part of the afternoon workable unless the area is enclosed and dehumidified.

Question 5

Can you coat a floor in winter?

Accepted Answer

Yes, but cold slabs are the constraint rather than humidity. Concrete retains overnight cold well past sunrise, so the substrate can remain at or below dew point until mid-morning even as the air warms. Measuring the slab directly, rather than assuming it matches air temperature, is essential.

Dew Point Calculator