Most, or probably all, filler manufacturers design and recommend them to be used over clean and prepped (sanded with coarse 36-grit), rust-free (sandblasted), dry (free from moisture), bare metal. They will stick to epoxy primers with mechanical adhesion. Body fillers do not chemically bond with epoxies. If you put filler over epoxy primer, it has to be fully cured, with no solvents such as thinner or reducer left in the primer, and still should be sanded with a coarse grit and cleaned. In other words, using epoxy primer under filler is a wasted step that may or may not cause adhesion problems later on.
This is posted by a Bodyman, Manufacturers Rep, Sales Rep.
I agree ..
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