Applying Body Filler

What is the best way to apply body filler; on bare metal or over epoxy primer? I've heard both ways, but don't know which way is better...Any suggestions?

I don't think there is an absolute answer to this question. I have always applied body filler over properly ground bare metal. I use 24 grit and cross grind to assure proper adhesion. However, some manufacture recommend that you apply epoxy primer before applying body filler. This seals the metal and prevent corrosion. Epoxy primer has a tendency to gum up when sanding though. I guess to best answer the question is to find what the manufacture suggests and follow recommendations. If anyone has used epoxy primer before adding the filler let us know how you like it.

Ive done both, i perfer to go over bare metal. Honda recommends filling over a primer.