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Old 08-06-2006, 01:08 PM
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Painting Plastic/Polyurethane Panels

I ordered some ground effects and new fenders for my wife's 96 Camaro convertible (my son took it into a ditch and it tore it up pretty good). I have the base coat, clear coat, and flex additive. What I am wondering is if I have to primer the plastic? Panels say to sand with 800 grit or finer, and then to follow paint application instructions.

I am thinking that if the plastic is clean, it may bond properly. I am concerned that the primer will crack and flake on the panels that flex, so I should I go without primer?...........

Thanks for the help.


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Old 08-06-2006, 09:14 PM
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You do not want to just "prime" it. If you go to the store you got your paint at they will have a "refinishing guide" for plastic parts which will include the manufacturer of your paints adhesion promotor for plastic parts. You could follow that guide or you could get an aftermarket adhesion promotor like SEM or Bulldog and follow their instructions. PPG has a great adhesion promotor by the way.

And you do NOT need any kind of flex additive with most paints and clears these days. That is a product from the dark ages.

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Old 08-07-2006, 07:17 AM
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I like to cut a bit of the plastic from an inconspicuous area and put it into a cup of water. Then use the saying:

"If it's a floater, it needs promoter"

IF the parts are polyurethane, they actually do not need adhesion promoter. If they are polypropylene or thermoplasic olefin, they do! So ID'ing the plastic is important, as is following the paint mfr's recommendations to the letter.

Also, if you are given the option to put some hardener in the base, DO IT! That will improve the strength, flexibility, and adhesion of the base, which is usually the weakest link in the system, especially with flexy parts.

P.S. Make sure the sliver of plastic does not have any air bubbles stuck to it, they may give a false positive on your test!

P.P.S. Lots of plastic parts come primed these days. If so, as long as you don't sand through the primer you are good to go. In these cases I use a gray scotch pad and some prep paste with water to thoroughly scuff the primer without breaking through...
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Old 08-08-2006, 08:31 AM
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We paint plastic bumpers everyday at our shop. One thing that you DONT want to do is use wax and grease remover. We don't use primer on the plastic either. We've had to many problems in the past with it. I wet sand with 1000 grit, wash with straight water unless there are greasy spots, then I add a little bit of soap. Apply the basecoat and then clear. 90% of the time we don't use flex additive.

Good luck
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