I painted my 86 several years ago using black DuPont Chroma base coat/clear coat and several cracks have appeared in the paint, they are each about three inches long, one on each door and one on the hood. What could have caused this and how do I fix it? The rest of the car turned out almost perfect.

 

Sorry to hear about your paint woes. Is that on the top side? What yr vette? And what's the location?

I'm guessing if it wasn't from an obvious physical stress like someone sitting on it, or running into something, or something heavy against the car (something that would flex the panel) ....it's probably from expansion/contraction. At first sight, it does look like the kind of crack that would result from being physically stressed. But from an expansion/contraction standpoint, Black paint get's hot. Expands more than most other colors. Then cools down in the shade and at night. That repeated many times for years can cause cracking. Even moreso if there's a thick coat of primer or thicker substrates beneath ...featherfill or bondo. If thick primer was put on, it's important to allow it to fully cure. Not well cured substrate might cause something like that??

Either way, what can you do about it now? Ultimately to fix it 'right' the crack needs to be ground out/down as far as the crack goes (which might just be the paint and primer) ...do the necessary bodywork, and repaint and re-clear (probably the whole panel). There might be some blending of the new clear to melt into an area ...because older Corvette panels blend into each other.

For the short term...this year, if you wanted to, a guy could daub some black single-stage paint into the crack. Fill it up over a few applications and let it harden. Then, once it's built up above the surface of the current paint, wetsand the new repair paint down smooth to the paint surface. If you built it up enough, it'll be perfectly smooth once wetsanded. Start with like 600# (wet) on the new paint, then switch to 1200 and eventually 1500#. Then buff the whole area to a nice luster. That'll produce an almost invisible repair (black on black) which will get you through the car show season with hardly anyone and even yourself noticing ....if you want to make it mostly invisible for now. Then come back for a more comprehensive repair, say, over the winter. Just a thought. And if it was me, I'd probably get a cheap bottle of 'testors' enamel model paint (black) ..for a couple bucks, then pour some into a small paper cup, and add a small amount of hardener. That will accelerate the curing process.

I'm not suggesting a quickie, well, I guess I am for now, unless you want to do a re-finish in that section now. But black on black usually makes a good-looking repair. And then you can come back to it when you don't mind having the car out of commission for a while. And maybe it'll turn out good enough you can leave it a yr or two to make sure no other areas crack in the future (and if they do, make all the repairs at once). So you have some options. Sorry, but best of luck

 

The locations are on the doors and hood, not any place that would be stressed or damaged. Car is in the garage and rarely driven. No bondo, original paint was sanded to primer and then sprayed with epoxy primer several weeks before paint was applied. I still have some paint left over so one of these days.....

 

Ok. That's interesting to know and makes it even more of a mystery. I guess the key question is ...Is the primer cracked too or just the paint? How far down does the crack go? Does the cracking happen at the same height (appx) on both the fender and the door? Like rear of fender/front of door? '86 is SMC and that stuff is incredibly tough and durable.

About the only thing I can think off is either too thick of primer, or if the panels were flexed in hard enough at some point in it's past ....and cracked the surface of the SMC (and hairline crack not noticed during the repaint process), something like that would re-telegraph through. Because it appears like a stress crack. Might not have happened, but that's about all I can think of. It sounds like you guys did everything right during the paint process. Maybe someone else here has other ideas. You might run it by a couple 3x bodyshops and get their individual takes ...they can put their keen eye on the cracks and maybe spot a couple additional clues that lead to a good answer. If you get some, come back and tell us what they discovered.

You don't have a high-school kid living in the house?? ha ha

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