Powder coating is no different from any other "compliant" coating. What that means is that when the Clean Air Act went into effect, many of the older paints that had a lot of solvent (high VOC) in them were no longer able to be used. These older, high solvent paints, had the ability to "cut through" thin layers of oil or soil and bond to the metal. As newer coatings were introduced such as water based, high solids/low solvent, powder and E-coat it quickly became apparent that these coatings required very clean substrates for good adhesion and performance. Powders are not unique, but they do require a clean surface as does any modern coating.