Original clear coat paint failure Options

[Cal]

My metallic silver '74 2.0 was repainted back in the mid 80's because of supposed clear coat failure. Was this common back in the day.....if so, why.....what caused the paint to fail?

[Amphicar770]

Saw this on another forum .....
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Tom, I worked for PPG (Resins and Coatings Division, Automotive OEM and Refinish) for 16 years, starting out as a chemist and ending up in sales. That said, I'll tell you a few of the causes for the problems you showed us.

Number one: Extreme temperature variations cause delamination between the clearcoat and the basecoat color. This will also rarely happen between the basecoat color and the substrate primer. Basically the clearcoat will expand and contract at a different rate than the basecoat color in extreme heat or cold. It actually happens more often on areas of the car where snow, ice, or frost accumulate. It can also be accelerated in areas that are subsequently heated quickly, such as a hood over the engine.

Number two: Acid Rain, as previously mentioned penetrates the clearcoat surface and breaks down the chemical bond between the clearcoat and the basecoat color. Again, this will cause a delamination between the layers since once the chemical bond is destroyed, only the weaker mechanical bond remains. Like the above reason, usually occurs predominately on top surfaces for obvious reasons.

Number three: More likely on repaints...recoat sensitivity, or not enough dry time either between the basecoat color coats and the clearcoat or not enough flash time between coats of clear. Again, unlikely on OEM and will usually show up much sooner in the form of "solvent popping".

Number four: Poor compatibility between the clearcoat and the basecoat color. I would think Dodge would know better than to do this but I've seen it on OEM before. You can't just put any clear over any substrate. In the old days when I first started, guys used to try to put acrylics over laquer (
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). The acrylics were usually much "hotter" and would dissolve the laquer under them. It can be done but usually with an intermediary barrier coat.

Number five: Insufficient clearcoat applied (or even some has been removed by color sanding or buffing) causing the clearcoat to provide a poor UV and chemical barrier. In the late 80s and early 90s the Big 3 were big offenders of this one. They were only allowed to spray a certain quantity of VOCs so rather than paint less cars, they just used less clearcoat on the same number of cars. We all remember the cars and especially trucks running around with paint peeling off back then. Well, there wasn't enough clearcoat or even colorcoat UV and chemical barrier protection to keep the primers from degrading so both the chemical and mechanical bonds were destroyed under the topcoats. It's like leaving something primered and never painting it. After a while the primer looks like chalk. This is another unlikely scenario based on the pictures you posted.

Number six: Poor waterbourne technology. Again, based on the VOC regulations of the time, auto manufacturers used a significant amount of waterbourne materials. Unfortunately, the technology was not very advanced at the time and the protection provided by these materials was substandard at best. Just about anything would penetrate these clearcoats, including water if left to absorb long enough (e.g. snow pack on the roof or hood). This scenario is also likely, based on the period your car was built.

There are a few other possible causes as well, but I could go on forever and a couple of these are most likely.

The bottom line is, the only fix is to sand it down (no chemical stripping) or media blast it off and repaint.

Good luck, hope this helps.
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