From my personal experience, epoxy primers such as PPG DP90 are better suited as a sealer which you recoat after the recommended flash time with your top coat. The epoxy can be mixed as a primer or as a sealer.
I have always had better success spraying bare metal with an (acid)etching primer. These primers generally mix 1 to 1 and are very thin. You will spray 1 to 2 light coats that are nearly transparent. Once it flashes you can scuff the surface with a red scotch brite. At this point you can use body filler where necessary and then move on to your 2K urethane high build primers. Once you have sanded the 2K primers and your are ready to top coat you will need to seal the vehicle. You can now use the epoxy as a sealer or use the sealer recommended by your paint store. You can top coat epoxy with acrylic enamel, single stage or basecoat/ clearcoat. It is best to use one system from start to finish such as PPG, Sikkens, or Dupont.
