When using conformal coatings in general, what causes a "milky" cure or white "foam" on the substrate?

In almost all cases, the cloudy or milky cure comes from coating in higher humidity conditions. The white foam (from an aerosol) is caused the same way. We have the following suggestions:

1. If possible, allow the substrate and coating material to come to approximately the same temperature when applying.
2. Avoid applications in RH > 60%. High humidity ranges will discolor some coating resins and will start curing others. Besides the aesthetic value, it certainly may affect adhesion to the material.
3. Specifically on the silicone coating, if the resulting application is foamy, increase the focal point of the can, ie back off to about 10 -12” from the substrate & make 2 -3 light passes rather than one heavy pass to coat the board.