Body filler is designed to bond to bare, clean metal. I always feel more comfortable if the metal is scratched a bit; at least as aggressive as 80 grit. Spreading filler is not an exact science so I’ve put masking tape along the body moulding and the body panel seem so filler does not get into the creases and crevices. The masking tape was peeled before the filler hardened.
To get a flat straight finish typically will require the use of a sanding block however, we live in the real world where machines are wonderful for saving time. I use a 6 inch dual-action (DA) finish [palm] sander just to knock the rough areas and for initial shaping.
Once the filler is sanded and even, there are likely to be ‘pin holes’ and deeper sand scratches that need to be filled. Glazing putty as a final coat with a new spreader and a final sanding with 150 then 220 grit should make the filler ready to be primed.
While priming is a good time to use the shine from the initial wetness to check the straightness of your bodywork. It’s even better if you have a portable lamp to set at one end of the panel. The primer I’m using is the the etch primer that needed to be applied right after manufacturing. I use a brand that is both a metal epoxy and a two part filling primer/sealer. It has some ‘body’ to it. Many of the etch primers are the consistency of water. If you are using one of those, it is necessary to follow up with a 2K urethane primer to make sure the 220 grit scratches get filled. As a final step a ‘guide coat’ of a contrasting color is misted over the primer. In the next article, I’ll show how the guide coat is used – thanks for reading.