Coating over rust, scale (oxide layer formed on steel during the hot roll mill processing) or any corrosion can create future issues of delamination, peeling and flaking. Other issues caused by coating over rust are you will loose the smoothness of the coating. We recommend media blasting your parts that have rust and scale with garnet media that will not impinge the metals. Media blasting will remove soils and contaminants and prepare the parts with a sa2 white finish. Giving the parts the best adhesion for paint possible.