raw plastic prep.
#1 Scuff part with grey scotchbrite, wet with soapy water solution. get the backside too. the purpose here it to scuff for mechanical adhesion and remove silicone mold release agents left from the molding process.
#2 scuff again, using a water/alcohol solution. 50/50. be thourough(sp) with the scuff getting every last cemtimeter. rinse agian.
#3 dry well, and inspect the part. fix any gouges with 500 grit and/or filler putty. part should be perfect to the touch. if you can feel a scratch with your finger, it WILL show up in the paint. now is the time to address this stuff. part should be uniformly scuffed and dulled all over. edges, corners, everything. do not half-a$$ this step.
Painting process starts with a wax/grease remover solvent wash, wipe away all traces of cleaner. This is best left to a good body shop.
#1 wipe with tack cloth all over, get all the dust off.
#2 first coat of paint is plastic adhesion promoter called Bulldog or equivelant. readily available in spraybombs. this is good stuff. mist on the coats, 3 light coats. wait between coats, do not run this stuff.
#3 base color, spray till covered, 3- 5 coats. again, do not run this stuff. be patient. add hardner to the base to increase flexibility and chip resistance. Many painters will not add the hardner cause it takes longer to flash. However, it is critical with urethane parts.
#4 Clear. this is where you add the flex agents. to the clear. If your paint system allows, see if you can use the same hardner in the clear that you used in the base. this will add a small bit of insurance, helping keep shrinkage rates uniform between layers and provide adhesion on a molecular level.
The fact is this. all modern urethanes are quite flexable, but paint does NOT stretch. if you hit something, the paints gonna crack from the stretch, i.e. lack of tensile strength. But as you heard before, it's 90% in the prep, parts need to be really, really clean, and scuffed well.
Hope this helps explain the process. there are many ways to do this. this is my method.
94 V8 on 17" custom paint, R.I.P
97 Mark VIII LSC yeah
08 Ford Edge, white for now