Questions for the painters...

I have never sanded an epoxy primer, IF I use epoxy as a sealer BEFORE topcoat, it is recommened to be reduced. If I am not happy with surface I would spray a sanding urethane primer and sand it. Then seal and topcoat. BUT I claim to be NO pro bodyman but a guy that has painted more than a few.
Anytime you change companies with the various primers, paints, you run the risk of a problem. Just like using a metal prep (acid) then going to a epoxy, IF not neutralized there can be a reaction, depending on the make up of the epoxy. Also some co.'s epoxy requires a "set time" others not.
I have used epoxy from PPG, SPI, TCP Global. I have b=never had a problem, but I am aware of the characters of them all. Also ya got to have the correct pressure and tip size!