Dtm primer question.

Another thing to know:
Self etching primers are intended for smooth bare metal, not for sandblasted metal.
Self etching primers should never be sprayed over sandblasted metal. Once sandblasted, the steel is slightly porous, and will retain some of the acid in the self etching primer. This can cause problems with adhesion and rust too. Epoxy primer over sandblasted metal only.
Self etching primers are a lazy mans way of avoiding the metal prep stage. A one size fits all product that when used right, does work, but really isn't the best choice.
When you sand steel, especially with finer grits, it gets smooth and shiny. Epoxy primer sticks and seals better than anything else, but shiny, smooth metal should really be etched with Metal Prep acid, rinsed to neutralize it, and then have epoxy primer sprayed on. The Metal Prep dulls the surface, cleans and preps it by adding tooth to the metal. Epoxy primers will bond better to the Metal Prepped surface plus it helps avoid corrosion. The factory did it this way.
Do not Metal Prep sandblasted steel either, for the same reason self etching primers should not be used in sandblasted steel.