Here is the problem with painting plastic. During the manufacturing process there is a substance called a " mold release agent " that is applied to the inside of the mold. This substance allows the part to pop out of the mold easily. The problem is that this substance gets transfered to the part and paint does not like it. This stuff has to be washed off properly and then an adhesion promoter needs to be applied. I had been using PPG paint systems up until 2004 and we had the worst luck with getting paint to stick to new unprimed bumper covers. All asian auto manufacturers, with the exception of Honda / Acura , ship out the new bumper covers without any kind of primer on them. They are in a raw plastic state. They must be treated properly. We switched to a paint system owned by DuPont called Standox and have not had a failure in six years. Standox's prep system uses a plastic cleaning paste in which you simply use it as a soap and wash the bumper with it. Then you spray on a coat of plastic primer, wait 20 minutes, and start spraying your basecoat ( color coat ). If you dont do this the paint will not stick, I guarantee it. If I was to paint my black plastic trim pieces, I would use the very same process. I do not trust the rattle can systems. They tend to make things sound so easy and simple, usually with less than desireable results. Now with that said, some auto manufacturers have what they refer to as " unpaintable parts ", meaning paint will not stick no matter what you do. It has something to do with the plastic material used. Some parts you may recognize would be the lower cladding pieces on the Chevrolet Avalanche. GM claims that they cant be painted, I have never tried it though. If you've ever gone to your local round track races you've seen the cars with generic white front ends. These plastic parts are unpaintable. Believe me , I've tried. The best way to paint your trim is to remove it, clean it, prime it, then paint it.
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