I really like the DP primers. I start with a bare metal surface that has either been sandblasted( chassis parts ) or well sanded with 60 or 80 grit( sheet metal ). Then cleaned well with wax and grease remover. I've applied filler over it and have had no problems so far with adhesion. I use a Devilbis Finish Line gun with the 1.6 tip and cheat a little by upping the inlet pressure on the gun a couple pounds. Seems to help with the orange peel. You can also reduce the DP with a DT reducer to use as a sealer for final top coats and this also sprays nicely.