Phospheric acid

If you have the parts in raw metal I would sand them to level the pitting of the sand blasting first. Then you can use a self-etching primer or an epoxy. The activator in the self-etching primer is phospheric acid. If you use epoxy primer on some you do not put etching primer down first.

If you have the parts in raw metal I would sand them to level the pitting of the sand blasting first. Then you can use a self-etching primer or an epoxy. The activator in the self-etching primer is phospheric acid. If you use epoxy primer on some you do not put etching primer down first.

I have never used the product that you mention. I can, however, explain my own experience with phosphoric acid-based metal treatments for steel from both DuPont and PPG. Both of these treatments are two step systems. DuPont’s first step is with 5717S, "Metal Conditioner" and second step is with 5718S, "Conversion Coating". PPG’s first step is with DX579, "Metal Cleaner" and second step is with DX520, "Metal Conditioner". I believe it is basically the same stuff from either company. Both companies state that the second step is necessary. I have experienced the light flash rusting (in spotty areas) immediately after the water wash following the first step...as you mention. The second step though, even after the final rinsing, turns that light rusting into a whitish cast that is said to be zinc phosphate. Priming of the surface should take place immediately after drying.

I doubt you did anything wrong. Just make sure that there is not a second step somewhere in the fine print on the label that you may have overlooked. I can link you to the technical data sheets from DuPont or PPG that cover this process if you wish.

Rod