If I am spraying a car in PPG paint then I use the DP LF series of epoxy primers over blasted and sanded metal. The data sheet does not call for using a etch first on steel so I don't use one. It does call for one on aluminum or galvanized metal.
If I am Spraying BASF(Glasurit, RM) then I use RM's EP series of epoxy primers. The data sheet also does not call for a etch so I don't use one.
The blasting company I use uses a sand/plastic mix so I can have all exterior body panels done with no warping. The downside is the finish doesn't have much tooth and the plastic leaves a residue. I have to go over the entire car with 80 grit when I get it back.
I have the cars blasted on rotisserie, inside , outside and underside so it is not possible to clean and blow the car out (which takes a day) sand the whole thing and epoxy in a day. The process takes about a week. Once it is covered with epoxy then I start grinding and welding. If done before spark slag/welding spatter sticks to the bare metal and has to be sanded off.
I have never used POR 15 and cant comment on that but I will say that as long as I have known Gary, he is not one to shortcut things so I would trust his evaluation on that product.
I also agree with Gary, it drives me crazy to watch bare metal groped on tv shows, same with bare hands running over sanded primer.
Where you live does have a lot to do with it. My dad blasted his mustang a year ago with out coating it and there is no visible rust on the car yet.
Good luck with your project!
