Epoxy really should be applied to bare metal from what I've read.  You should use an etch wash containing phosphoric acid prior to shooting the epoxy.  You could use an etching primer, but the active etching ingredient in etching primer is phosphoric acid, so to my mind its easier to wipe on a liquid and tack cloth the car down rather than mix and shoot ANOTHER coat of paint.  You may be able to shoot it over a sealer though.You can absolutely use filler over epoxy primer, in fact that's how most shops would do it.  The issue you get with filler over bare metal is that filler can absorb moisture.  If there's any way for moisture to get in (including absorbing it from the air) the filler will corrode the underlying metal, swell, and eventually fail.  The other consideration is that epoxy is going to create a better bond to bare metal than the filler, then the filler creates a better bond to the epoxy than to bare metal.   My advice would be to go to the local store selling automotive paints and ask them these questions for the particular products you are going to use.  The biggest mistake people make is using products from different manufacturers which are incompatible.  I've seen fresh, beautiful paint that cost thousands of dollars come off my buddy's Impala in sheets because of this. 

I'd check out the SPI epoxy

Definitely use SPI Epoxy! I stripped my 66 coupe down to bare metal using aircraft stripper then a DA with 80 grit. Cleaned it well then shot one panel at a time with SPI Epoxy. That stuff is tough! I've sat tools on it, who knows how many kinds of chemicals have been dripped or dropped on it, but it's still tough and protecting the car. Like mentioned the Epoxy primer isn't good when left out in the sun as the UV rays will make it chalky. Anyway after it has sat you'll need to scuff it using red scotchbrite before re-coating, applying filler, or paint.

On edit: SPI says you can use the filler over or under the primer, most of the pro painters on the SPI forum put filler *over* the epoxy. Just FYI.

Last edited by Raymond_B (12/11/2018 2:11 PM)