How To Fix Cracking Paint

This small crack appeared... 

   

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This small crack appeared on the corner of the extreme rear edge of the quarter-panel. While you might be tempted to simply grind out and redo the filler, resist that temptation and go all the way back to bare metal to find out why the crack occurred in the first place. If you don't do it the first time, it's very likely you'll get a second chance at it.

Whoops, there is a big crack in your paint. You didn't see it before, but there it is. Was it the Bondo that cracked or was it the application of the paint? How do you find out? We're going to show you. There are many reasons you might need to spot-repair your otherwise perfect paint job, such as a door ding, a paint bubble, or a large scratch, but we are going to show you a worst-case scenario-ours was a sheetmetal failure under the bodywork.

To get some expert advice on how to deal with this issue, we spent a day at Muscle Car Restorations in Chippewa Falls, Wisconsin. These guys are well known for their world-class full restorations, but they are also glad to take in partial work. This is doable in one day, so you shouldn't have to miss your next event.

We started by thoroughly cleaning...        read full caption We started by thoroughly cleaning the area with PPG DX320 Wax and Grease Remover and then carefully ground out the area with a 3M 3-inch 36-grit Roloc disc. Watch out that you don't allow the disc to touch another finished part of the car or a piece of chrome trim. A 3M Roloc bristle disc will help you to clean out the hard-to-reach places without removing any sheetmetal.

A small screwdriver or pick...        read full caption A small screwdriver or pick was required to clean out the crevices. What was uncovered was a seam that was brazed together at the factory. Perhaps the body filler didn't stick to the brass properly or maybe the brass just wasn't holding the seam together anymore. Whatever the reason, the seam must now be welded to prevent any future issues.

After removing the old factory...        read full caption After removing the old factory brass, we started to weld up the seam. This kind of welding can be a little delicate in that you must get good penetration while avoiding overheating the surrounding metal. The trick is to slowly build up the area with small beads while quickly quenching each one with compressed air.