The Stovebolt Site Forums The Shop Area Paint and Body Shop paint lifting off

I painted my 53 truck myself. I'm not very good at it, but for the most part, I'm satisfied with it, except for the right front fender. I had all of the sheet metal sand blasted to bare metal, and epoxy primer applied. When I applied primer/filler to it, a big blister rose up about the size of a half dollar. I sanded it out over a big sized area, and cleaned it well, and applied primer again. The blister reappeared. So, I sanded it down to bare metal and started from scratch. I applied Kirker epoxy, then urethane sanding primer, then paint, which was PPG shopline urethane enamel. Everything seemed OK, but a few days later the paint started lifting up, about where the original blister was. Then it started cracking and peeling off, in the same general area. I was so discusted that I walked away for several months. Now I'm ready to get back at it, but I don't know where to start. Just to elaborate, I did use a name brand wax & grease remover prior to applying every coat of everything. I was careful to follow directions regarding timing of recoating, etc. I feel that I need to apply a really good sealer this time, after stripping it all down, but I don't know what to use. I always thought that epoxy was a good sealer.

To me the weirdest thing about this is that the problem only showed up on the right front fender. I used the same process on the remainder of the truck, and had no problems. I hate body work, but I especially hate doing it over. Your help will be much appreciated.

Mike - I’m no expert in the painting realm, but it sounds like there is a contaminant present that isn’t being removed by sanding and degreaser/wax removers.

Could be something containing silicone was spilled on the fender, or maybe on cloths used in the cleaning process have made contact and left residue on the fender.

Not sure what might be used to decontaminate the fender, when stripping it down again, but reading other Bolters comments, it’s clear that it’s a very difficult process.

Others should be along to offer more insight.

I won’t offer advice but between which layers is the unbonding happening? Looks like it’s first layer over the metal? That rust. Did sandblasting peen in rust?


Good news is At least it’s on a fender…..

Chuck

Looks like it could also use some better mechanical adhesion. Maybe some 80 grit. Clean the steel before sanding so you don't sand the contaminants into the metal.

Yes, it peeled off clear down to the bare metal. I hired a sandblast guy to do the blasting. He also sprayed the epoxy on it. So, I can't really say whether he blasted rust into the metal. But the fender in question was no more rusty than the rest of the truck. So, why just the one fender?

I agree that it needs batter adhesion. I assume that you're talking about 80 grit on the bare metal, right?

The bare steel should be treated with a metal cleaning liquid, Metal-Prep, Aluma-Prep, Galva-Prep as examples. These solutions clean the metal chemically and also etch the surface to increase adhesion. Apply the solution with a CLEAN/NEW brush, scratch pad, cotton rag. Watch the surface of the steel as you clean the area, you will be able to see the liquid bead up if the steel is still dirty, the solution will "sheet" when the surface is clean, then rinse with clean water.

If your blaster didn’t clean the metal after blasting and before shooting the epoxy, dust would do that. Normally you can shoot primer after blasting (and after cleaning) as blasting gives the metal excellent “tooth”.
You should take it back down to bare metal and CLEAN.

Just looked closer at the photos.

FIRE YOUR BLASTER.

Looks like you were set up to fail on that one fender.
I was always under the impression that epoxy primer was non reactive to the primer/paint you put over it, so you had nothing to do with it lifting off the steel.
Each brand of epoxy primer has a specific topcoat window to get the next coat on, or you need to follow a specific TDS process before overcoating. Do you have the TDS (tech data sheet)for the epoxy primer?

Chuck

PPG has DX579 and DX520, these are used for steel prep.

Right.

The rough texture left by the blast media is creating thousands of places for rust to get started. Your blaster guy should have used glass beads, not sand, as his media choice. Now you need to use metal prep (phosphoric acid) to deep clean the metal and neutralize any imbedded rust, before giving the metal a thorough HOT water scrub and an immediate primer coat before the flash rust can form again. Metal that's been pitted by overly aggressive blast media is VERY hard to work with.
Jerry

I would strip the whole fender and start over. If my blaster was also priming I would want to be there or at least inspect it before primer. JMHO

It's easy for me to look back now and see that I should have applied the epoxy myself, after proper metal treatment. I guess I'm lucky that it's just one fender that has a problem. Yesterday I removed the fender and took it to a friend who has a body shop. He is going to strip it to bare metal, and start from scratch. Prior to that, he is going to let his PPG rep have a look at it and see what his opinions are. I just didn't want to get back into it myself. I don't mind painting, but one time is enough for me, and I didn't want this to turn into a never ending project.