Q. Can we use water-based paint for touch up on powder-coated parts? We powder coat various CNG gas cylinders, and we also want to do color-band painting on these cylinders for identification. Is any surface preparation necessary? What should the curing time and temperature be? K.K.
A. It is possible to apply a waterborne paint over powder, but adhesion may not work. A solvent paint is most likely going to be better, because it will wet the surface better and adhere better over powder.
Sand the surface, remove all loose dust or paint, and do a test part to see if the material sticks. The best possible paint to use is a two-component epoxy for indoor use or urethane for outdoor use. The two-component paint is catalyzed so it can be dried at a low temperature (180°F/80°C or lower). Keep in mind that spot touch- up will likely not match the color precisely and may not hold up as well over time as the original powder