Ask the Expert Question-and-Answer Archive

by Ron Joseph

Effect of Humidity & Temperature on Painting

Q. We are using Polyurethane paint which is applied on FRP. What effect does humidity and temperature have?

A. Temperature will affect the curing time of a two-component polyurethane. As a rule of thumb, (in other words this is simply an estimate), for every 10°C rise in temperature, the curing rate will be cut in half. More simply put, as the temperature increases, the pot life of the coating will be shorter as will the time for the coating to cure.

Polyurethanes coatings are sensitive to moisture. In fact, it is the curing agent, usually Component B that is most sensitive. The technical datasheet of the product should tell you what humidity is reasonable; however, in general you should try to control the humidity in your facility to below approximately 70%. While this is not a hard and fast value and it is possible to apply polyurethanes above this level, high levels of humidity can affect the properties of the coating and can cause it to gel sooner.

Good luck,

Ron Joseph