I just sprayed my first epoxy primer (black) over a fender that had bare metal and body filler. I applied two coats about 20 minutes apart. The coverage over the bare metal looks great, but I can see the filler areas through the primer. These areas are fully black but show the filler location beneath the primer. I am a novice with these materials and techniques but have some painting experience from a long time ago. Is this normal? If not, any suggestions? Thanks