I am fixing to paint some urethane aftermarket fender flares.I have some primer for plastic.Is this all I need to prep with or do I need some other kind of primer over the plastic primer?I will be spraying them with a urethane basecoat clearcoat system.Any and all help is appreciated.Thanks.

 

Okay, first we need to know what you are dealing with. Are these bare urethane pieces? What I do on bare urethane pieces is to clean them with soap and water and wipe down with a wax and grease remover. They do make a prep cleaner for plastics, but I never had any problem with using wax and grease remover. I don't know whats really different about it. May be something like plastic pieces build up static electricity and maybe the plastic stuff the solvents aren't very flammable or something, don't know. Anyways, once the piece is cleaned, then sand. What you sand with really depends on the shape of the piece and if you will be priming it or not. If they are new and in good shape, you could probably just shoot on some adhesion promotor (probably what your plastic primer is) like bulldog after sanding and paint. I personally like to epoxy prime the piece and shoot on a little urethane 2k primer then guide coat and check it over for any imperfections before paint. Epoxy primer sticks well and seals, which is why I like to use it on bare urethane. Most of them don't sand real well though. If it is in good shape and you really don't want a lot of sanding and to use all that material, then I would just clean, sand with around 320 grit dry with a da, or with around 400 wet, wipe down again with wax and grease remover, apply a coat of adhesion promotor then spray an epoxy primer reduced as a sealer. Choose a color of epoxy that will help with coverage of your paint. Let the epoxy flash off for awhile and spray your paint. If you allow it to flash off long enough, you can lightly tack it before shooting your color. You won't need to sand the epoxy primer at all as long as you paint within its window, Most are at least a few days or more. I don't believe you would absolutely have to use any primer other then then your plastic primer, but I do.

 

Some paint systems call for the addition of an elastisizer additive..don't
know how necessary it really is.

 

Don't waste your time with flex additive. Big waste of money. Urethane paints are fairly flexable as it is and the flex additives leave the paint over time anyways. Flex additives are mainly to help with installation of the part, but if you trial fit and unless your are really flexing that bumper installing it, you should not have a problem without the flex. I never had a problem installing a part and not using a flex additive. Most important is to have a clean part and sand well with the proper grit, and you shouldn't have problems with your paint adhering well if you do this. I painted a cavalier a little over a year ago. The guy totaled the car not too long after he got it back. Hit someone and punched the front end in. The urethane bumper was twisted up pretty good. There were some spider cracks in the paint where the major hit was, but as far as I remember no paint was flaked off of it at all. I didnt' use a flex additive.

 

Thanks guys.Barring rain today,I hope to get these painted.