When choosing a primer there are a few choices. First check your local VOC regulations. KP21 is a 2.1 VOC epoxy primer for low VOC areas. KP2-CF is the national rule epoxy primer-both are designed for extreme durability and corrosion resistance over bare metals. Both sand very easily when dry with no shrinkage. You could also apply KS-10/KS-210 or KS-11/KS-211 over one of the KP primers or a sanded OEM finish as a sanding primer. Don’t take a chance and use some one else’s primer under your House of Kolor products. If our tests showed that an etch or wash primer and a fast drying 2K urethane primer would hold up as well as our epoxies we would make one.