Painting Over Powder Coating

Question

I’m a custom coater who supplies powder coated parts to industrial customers.  We apply mostly epoxy and polyester powder coating by electrostatic spray guns. Many customers would like to paint over these parts for various reasons. How safely can they apply their wet paint over our powder coated parts? 

Answer

Powder coatings are an excellent paint base. All paints will adhere to polyester and epoxy powder coated surfaces provided there are no slip agents on their surfaces (added to paint and powder formulation to increase mar resistance). They can act as release agents and painting over them would be like painting over mold release. So use a material that has no slip agent in the formulation.  Otherwise, your customer will have to solvent clean or abrade the surface to remove the slip agent and obtain adhesion before repainting.

If your customer repaints, recommend using thermosetting acrylic, epoxy, polyester or polyurethane enamels.  Although they may not provide the same quality, air drying enamels including aerosol spray can paints will adhere as well. 

Question 

Can I safely paint over powder coating on my engine? I have a Harley with aluminum powder coated cases that I would like to paint black using high heat engine paint, is it possible? How do I prep it? 

Answer

Why would you want to replace a durable powder coating with an aerosol liquid paint from a can? It won’t wear as well and may chip easier. If you really, really, really want to do this, then the only sure bet is to completely remove the powder coating first. Grit blasting the engine parts using plastic media will do the least harm to the aluminum and yet remove the powder coating completely. If you don’t remove the powder first, you could have some inter-coat adhesion problems with the liquid paint and powder
coating.