Auto body repair & detailing: Refinishing bumpers on Jetta, vw jetta, wet coats

Question
Ken,

I need to refinish both the front and rear bumpers on my 96' VW Jetta. They are plastic, rubber, whatever and have numerous nicks and scratches from stones and such. The car is candy white in color. Will you give me a step by step for repair? I have done some body work before but have never dealt with plastics. Would I block sand with 600? Wet or dry? What primer to use? I have heard of a flex additive that must be used. Acrylic Urethane to finish or base/clear? There is also a channel in the front bumper that I would like to fill in and smooth over. What would I use for this? The car does not need to be perfect but I would like it to look better. Thanks so much!

Answer
I would use flex agent in the primer and clear coat. Sand the Flat areas with 320 grit DA paper with a DA sander and use 320 grit by hand on the contours till all the chips and such are gone to your preference. Then make sure the whole bumper is scuffed with either 320 grit or a scuff pad. Now your ready for primer.  I would use a urethane high build primer. Apply 3 to 4 wet coats let dry over night. At this point the bumper may need to be sanded and primed again as some times the plastic swells up or can look rough if so sand entire bumper with 320 Grit dry careful not to break through the primer to much then reprime with 1 to 2 coats of primer. After it is dry or if it don't need that step Sand the bumper with 400 grit wet Paper till smooth. Dry off water and scuff with fine scuff pad your now ready for paint. Wash the bumper with a pre cleaner to remove oils and such from your hands. I would use urethane clear-coat/base-coat. Also you can't fill a big groove such as the one you asked about with out it cracking.

                    THANK YOU FOR YOUR ?
                    KEN