Q. Are you aware of any uncomplicated, user-friendly pretreatments that are compatible with powder coating, will inhibit rust on surfaces with deep inset corrosion and will accelerate beneath the coating after the process is complete? J.R.
A. Iron phosphate works well with powder but has modest corrosion resistance if the coating is broken. Zirconium oxide products can be modestly better, and some contain other metals such as copper or titanium and are somewhat more resistant to oxidation. Zinc phosphate has very good corrosion resistance, but it also requires waste treatment and would not be considered simple or user-friendly. One of the best options is a primer. Thoroughly clean the surface by chemical or mechanical cleaning, then you can have the parts electrocoated or you can apply a powder primer. The primer provides exceptional resistance to moisture penetration and a thicker film with better edge coverage. The primer does a great job of stopping the undercoat creep you refer to.