Strip to bare metal inside and out, then shoot two coats of epoxy primer. I like using black.
This is the absolute best way to approach it.


Wait 24 hours and then lightly block sand the epoxy. It will work like a guide coat in showing you were your trouble spots are. Low spots stay shiny while the rest looks sanded.

You can apply filler over the epoxy primer without sanding the lows spots first if you are within the re-coat window (7 days on the epoxy primer I use).

Filler should be applied well past your low area so it can be feather sanded into the surrounding epoxy primer.

Once done with your filler work you have two options. You can shoot another coat of epoxy over the filler areas to seal them, or you can apply your 2k build primer. Either way is acceptable.

Generally 2-3 coats of 2k build primer is applied with plenty of flash time between. You will want a spray gun with at least a 1.8 tip size for the build primer.

Once 2k primer has cured apply a guide coat (I like 3m Dry) and then block sand with a fairly coarse grit sandpaper to remove the guide coat. This step is that gets your panel nice and strait. You will repeat this step as necessary using a finer grit paper like 180 - 220.

When you can block sand the panel and remove all the guide coat without sanding through to metal you are close to done. At this point I would shoot a coat of epoxy primer to seal the panel and then set it aside as you work on the other parts.

See the sticky post on using Guide Coat at the top of this forum.

I've read through this thread and have a question.

Have there always been epoxy/2k primers? What did body shops use 10/20/30/40 years ago? You read that the only solution is to use epoxy primer on bare metal. What did they used to use?

here's what I think I know.
40 and back it was lacquer and enamel primers, enamel primers were good ONLY for enamel top coats. lacquer was the rage, you could fill with it sand it easy and a lacquer top coat work good. the primer was poor quality compared to todays products. lacquer by its self couldn't get wet or be left outside water would soak right through it.
later epoxys were being used but shops shied away as they were to slow I can remember using DP-90 back then.
30 years back, 2 part filler primers came on and were the thing to use. I probably sprayed over a 100 gallons of it. along with the filler primers was etch primers they kinda went hand and hand. the etch was a good bare metal binder if you can call it that it was used first and then the 2 part primer was shot over it. alot of the 2part primers weren't direct to metal and needed the etch prime.
now days shops use etch prime then the 2 part primer or a direct to metal 2 part primer, it's a fast way to go for them were time is money. you don't need to use epoxy, etch will work also. I use both and prefer the epoxy most of the time for restoration work. if i'm doing a repair or need to get it out quickly i'll use the etch prim. I hope this didn't confuse you more.
Jay D.

Most bodyshops today still use etch primer for bare metal,
Epoxy is to slow a process for them.