Painting Over Powder Coating

Painting over Powder Coating

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?

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.

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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
coating. 

Powder Coating over Polyester Powder Coating

Q. Can I paint over powder coating? Will the paint adhere? One of our customers supplies coated aluminum castings to a small appliance manufacturer. He has a number of aluminum housings painted with a white polyester powder coating. Now the manufacturer wants castings in other colors. 

A. Paints will adhere to powder coatings, providing there is no slip agent present on the surface. Slip agents are often formulated into powder coatings to increase their mar resistance. Your customer’s powder supplier will tell you whether a slip agent is used in his powder. If the slip agent is present on the powder coating’s surface, it must be removed before painting by solvent wiping or sanding. If this procedure does not remove the slip agent, the castings must be stripped to bare metal.

After the appliance castings are prepared for recoating, I suggest using a polyester, thermosetting acrylic or polyurethane enamel to achieve the same high quality.