What can lead to paint "skin over" and trapping solvents underneath?

The phenomenon of paint "skin over" occurs when the surface of the paint dries while the solvents underneath remain wet. This situation can be particularly problematic as it can lead to poor adhesion and other defects. The use of heat guns or non-approved heat sources is a significant factor in this process. Such tools can generate excessive and uneven heat, which may cause the top layer of paint to form a skin too quickly without allowing the solvents underneath to evaporate properly. This rapid drying on the surface can create a barrier that traps the solvents below, leading to defects in the finish and potentially requiring corrective measures.

In contrast, using air compressors is typically associated with properly atomizing paint and can aid in even application, while using approved heat sources is designed to encourage proper drying without the adverse effects associated with excessive heat. Applying multiple coats of paint should be done within the manufacturer's recommended timeframes and can typically be managed to avoid trapping solvents if the application is controlled and allowed adequate time between layers. Thus, the use of heat guns or non-approved heat sources is the primary concern that directly leads to the issue of skin formation and solvent entrapment.