Technical Sanding DP40

My car appears to have been coated a long time ago in an epoxy primer. I've had the car for at least 14 years in storage and no idea of when it was coated prior to that but the only epoxy coating I know of going back that far would probably be DP40 or at least something similar. I used the stuff myself on another project maybe 25 years ago.
So, I need to do some body work and replace the rockers and some metal in front of the rear wheels. I started off with an 80 grit disc and it barely touched the stuff, so switched up to a 36 grit and while that was better, it wasn't exactly fast either. I don't know if I want to go any lower on grit as I don't want to overheat the metal. Obviously I have to get the metal clean for welding so what other options might be available? I'm not too keen on any type of sandblasting as the metal is fairly straight and don't want to warp it.

 

Don’t be reluctant to use your resources. Go to your local PPG vendor. Ask to talk to the Manager , not the expert behind the counter that worked on a garbage truck last week. The Manager !
Politely ask for the Local PPG reps number. Have him look at what you have . If you are going ahead with nice expensive finished paint in the long run , now is the time to get a plan.
Stretch

 

You can do your filler work over the top of DP primers.
I'd sand it with 120 grit, the thing about DP primers is they don't feather well.
You don't say if you're removing it or you are sanding for bodywork and build primer.

 

Plan out your patch panel area, wire wheel an inch or two out from your cut line, it will take DP40 off.
Weld your patch panel in, wire wheel any loose / burnt primer back another 2-3 inches. Feather the edge with DA. Shoot more epoxy on the repair.

 

"I need to do some body work and replace the rockers and some metal in front of the rear wheels."

 

If it is old DP it should come off without too much trouble. You can weld through it though. When you are ready to start the paint process you MUST sand the old DP or you will have adhesion problems. Scotch brite will work to give the new DP a tooth. You will have to shoot DP or similar over the old as nothing else will stick to it.

 

Weedburner 40 is spot on--thats what i would do

 

I used K36 sandable primer over DP90 that was rubbed down with Scotch brite. 25 years ago & have had no problems with it .

 

You don't need to only use DP over DP, once sanded thuroly all types of modern primer can be used.. Depending on the build of DP I sand with 180 or 120 grit then do filler work and prime with a high build urathane. I've gotten away from DP on painted surfaces on the body or finished frames etc. and use a epoxy that can be block sanded.
For removing the primer for welding I use a angle die grinder with a 3" disk usually 36 grit..

 

I would be wet sanding epoxy. I find it to be rubbery no matter what brand and what age unless it has sat outside and deteriorated a lot.

 

Agree any old primer that has cured, needs to be "cut / sanded" before adding another layer. The only time you can coat directly on top without sanding is within the recoat window the paint is spec'd for.

I doubt Ill ever work fast enough to hit a recoat window on primer. Im a 1 man show working on my own stuff, not running a shop. I always let it cure and scuff it. In my mind it provides a more stable surface and chance of compatibility issues goes down greatly when you let primers completely gas out.
Production shops, or good bodymen , work fast enough to have these concerns about recoat windows.