Quote:

If you put bondo over primer, will it stay? Or does it have to be strictly stripped metal?




I have never been a filler over any type of primer guy. Just the thought of trapping any uncured solvents under filler stops me right there.
I pulled this from another site. It pretty well confirms my thoughts.

Quote:

"OK--Here's the gospel on body filler/bondo over primer. I used to work as a technical/sales rep for the company that makes rage filler. I know the guys (chemists) that developed the resin for rage filler. I've been a bodyman/painter,sales rep and technical rep for 30 years. The resin in rage and other body fillers is fiberglass (polyester) resin. Today's resin technology makes the adhesion of these new resins as good or better than most epoxy adhesives (glue). They are designed to really stick! Also they are somewhat flexible when used properly. Most or probably all filler manufacturers design and reccommend them to be used over clean and prepped (grinding with course-36 grit) and rust free (sandblasted)and dry (free from moisture) BARE metal. They will stick to epoxy primers with mechanical adhesion-they DO NOT chemically bond with epoxies. If you put filler over epoxy primer it has to be fully cured with no solvents (thinner-reducer) left in the primer and still should be sanded with a course grit and cleaned. In other words- It's a wasted step that may or may not cause adhesion problems later on."