Type of Primer for Engine Compartment

[rscottm]

After sanding to bare metal, what type of primer should be used, self-etching, epoxy, others? I plan to go ahead and coat the bare metal so it won't flash rust. At a later time, I would then do a little filler and seam sealing work and then paint.

Can body filler be added on top of self-etching primer or would I have to sand it off and prime first with another type of primer?

[kenz240z]

I would recommend an epoxy primer. For best results, you will have to sand it again before you do the final prime/paint.

I have only used PPG Omni line of paint and the fellow at the paint supply store told me not to spray etch primer over body filler. What I have done is this: sand to bare metal. Apply filler where needed. Sand to desired contour. Mask over the areas with filler. Spray the etch primer (it goes on very thin). Spray on high build primer. Sand smooth. Spray epoxy primer (goes on flat, no sanding needed). Spray top coat.

It may also work to spray the bare metal with etch primer first, then sand down the areas where the filler needs to go.

[EScanlon]

Bare metal should ALWAYS be etched before anything else gets sprayed on top.

Whether that etching is done by using a metal prep solution (phosphoric acid bath) or it's contained in the primer (self-etching primer, whether that's an epoxy primer or not) it is the primary way of getting primer to adhere to the metal.

After it's been etched, or primed with self-etching primer (again, epoxy or not), then you can build up with Filler Primer, Bondo, or go to a Sealer or even to a Base coat of paint.

Take note that the acid bath, or self-etching primer, while it does help reduce the incidence of rust, it is not by itself rustproofing the surface. Given enough time the metal WILL rust through the primer if it hasn't been top-coated.

FWIW

E

[gorillaFart]

To add to EScanlon's post, make sure if you use a metal prep solution such as the phophoric acid (which smells strongly like rotten eggs) make sure you surface clean the metal thoroughly with the proper surface cleaner, or else your primers will react to the acid and fail.

Self Etching is particularly for bare metal only. and i would really only use it on spot repairs where bare metal is showing. And although Epoxy primer can be sprayed over areas of filler, it should be used over bare metal only because the idea is to protect bare metal. Epoxy primers are formulated to be the closest thing we can get to mimic-ing a factory E-coated car.

so if i were you, to make life easier on myself, i would work on each panel from begining to end, one at a time. Meaning i would take the fender for instance down to bare metal then epoxy it, add the filler, sand/shape it, then add the high fill primer, sand it and shape it, then add your seam sealer...and not till im completely done with doing that will i move onto the next panel. if you are trying to sand the whole car down to bare metal at once, you'll be fighting surface rust everywhere. Doing it this way will prevent that. after the whole car is in primer, you can base and clear it all at once.

hope this was of any help