4.1 Coatings that chemically change during the curing process, such as epoxies, vinyl esters, polyesters, alkyds and urethanes, become more resistant to solvents as they cure. These coatings should reach specific levels of solvent resistance prior to being topcoated and prior to placing in service; the levels of solvent resistance necessary vary with the type of coating and the intended service. Rubbing with a cloth saturated with the appropriate solvent is one way to determine when a specific level of solvent resistance is reached. However, the level of solvent resistance by itself does not indicate full cure and some coatings become solvent resistant before they become sufficiently cured for service.

4.2 The time required to reach a specific level of solvent resistance can be influenced by temperature, film thickness, air movement and, for water-borne or water-reactive coatings, humidity.

4.3 The test solvent's effect upon the coating varies with coating type and solvent used. The coating manufacturer may specify the solvent, the number of double rubs, and the specific test results needed.