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Mon Jul 03, 2006 8:33 am

When working an existing painted panel to bare metal in a small area to remove rust, what is the best way/product to prime over the bare spot? Is it bad to spray epoxy primer over existing paint? Hope this makes sense.

Mon Jul 03, 2006 9:44 am

I don't think it's bad, just make sure the paint is scuffed up sufficiently for a "mechanical" bond to help the epoxy stick. I would guess 400 or 600 grit, but then again I'm no professional. Hopefully one of the other regulars can chime in.

I think the only situation that may be suspect would be if there were several previous layers of paint. On my squareback, for example, there were at least 5 different resprays, so I took it down to bare metal.

Mon Jul 03, 2006 10:17 am

PPG has Primer called DP40 or DP90 (color choice) It can be used over bare metal or over paint as a sealer.. great stuff but pricey.

Mon Jul 03, 2006 12:00 pm

Epoxy prime over paint - no problem - sand down the paint to remove any glossy sheen and give it a good scuff -

This is what I'm doing -> Electric orbital sander at 60 grit, electric orbital sander at 100 grit, hand block sanding dry with 220 followed by 320 - that is good enough for a high build epoxy primer...this takes off a fair ammount of the paint and leaves spots of primer showing thru

one thing to keep in mind is that you do not want the total thickness of the paints and primers to be too thick - so it doesn't hurt to sand off a little too much of the existing paint...

a second thing to keep in mind, is that after you repair the rusty spot, any metal that is showing needs to be etch primered before epoxy primered (at least with Dupont and "Five Star" products)....try not to get the etch primer on existing paint (it won't adhere well)...

Mon Jul 03, 2006 6:14 pm

marklaken wrote: Epoxy prime over paint - no problem - sand down the paint to remove any glossy sheen and give it a good scuff -

This is what I'm doing -> Electric orbital sander at 60 grit, electric orbital sander at 100 grit, hand block sanding dry with 220 followed by 320 - that is good enough for a high build epoxy primer...this takes off a fair ammount of the paint and leaves spots of primer showing thru

one thing to keep in mind is that you do not want the total thickness of the paints and primers to be too thick - so it doesn't hurt to sand off a little too much of the existing paint...

a second thing to keep in mind, is that after you repair the rusty spot, any metal that is showing needs to be etch primered before epoxy primered (at least with Dupont and "Five Star" products)....try not to get the etch primer on existing paint (it won't adhere well)...

How would you suggest masking off around an erratic line to prevent etching primer from getting on paint??? I've been wondering about that.

Mon Jul 03, 2006 7:25 pm

no ,
go larger with your paint,( sanding as well)
and feather it

Wed Jul 05, 2006 3:47 pm

spook wrote: no ,
go larger with your paint,( sanding as well)
and feather it

I'm not sure I completely understand what you are saying. How do I keep etch primer off the paint?

Wed Jul 05, 2006 7:36 pm

Rumdum wrote: spook wrote: no ,
go larger with your paint,( sanding as well)
and feather it

I'm not sure I completely understand what you are saying. How do I keep etch primer off the paint?
You really do not need an etch primer on the bare metal in small spots, a good quality brand of a high fill primer will adhere to both the sanded metal and paint. I only use the etch primer if the whole panel is completely stripped of paint and i will not be bodyworking that panel anytime soon..........then again i usually use a sealer for that as well.

Thu Jul 06, 2006 6:45 am

Sorry Spook, I'm with Matt on this one. As long as the metal is clean (rust free). I make sure the metal is ruffed up with at least 80 grit.
I also ruff up exsisting paint with 180 before putting a high build primer on. You can't go too ruff in the first stages- I LIKE adhesion.

Thu Jul 06, 2006 7:41 am

Just a tip--Never tape off part of a panel when doing work. Always let a large area over spray. A tape line, say when priming and area, will become a big headache.