Filler on bare metal or epoxy primer?
I'm getting ready to strip a car to bare metal and apply filler. The sheetmetal has a lot of door dings and ripples so I'm planning on a skim coat over the whole surface to level it. It seems there are two schools of thought here. One says to apply filler to the bare metal then shoot primer over it. The other says shoot an epoxy primer to the bare metal, then apply filler. Which is best or do both work well?
If I apply filler to bare metal, do I then apply a self etching primer or epoxy primer after?
If I apply epoxy primer first, does it need to be "scuffed" to help filler adhesion?
When I sand the filler, won't it remove the epoxy primer anyway when I sand? Then won't I have to reshoot the primer and do I use more epoxy primer?
See Serge's Test Report Here
I've been trying epoxy under filler (here and there) for years and the only time I think there could be a benefit is over a seam or break in the metal substrate. The only reason to apply primer on a seam is so that any moisture that could get into the repair from the back wouldn't attack the metal as fast as it would without the primer.
Originally Posted by timinator
If you have a panel with dents I would skip the primer and go straight to the filler using two precautions....
1. Be sure to grind the surface of the metal using a coarse grit like 24 or 36.
2. Press your first pass into the scratches then (in the same coat) come back and lay the filler on more heavily on top.
Pressing the first pass into the scratches is a good idea for each application even when it's on top of a previous coat of filler. This will help stop pinholes and help the filler adhere better to the substrate.