Advice on Painting plastic cladding and bumper (1 Viewer)

[MSGGrunt]

I'm restoring/re-freshening a 1982 Mercedes 300SD turbo diesel and she is currently in the shop getting a complete paint job. The car has lower plastic body molding that was originally painted gray from the factory. This was easy to paint glossy black. Sand, clean and I sprayed with Rust-Oleum specialty Plastic paint, wet sand, then clear. I didn't use any etching primer, high build primer or adhesion promoter and I hope that wasn't a mistake. If so I have another complete set of moldings so I could do it again and learn from my mistakes.
I know I have read a lot about people having used Krylon Fusion with good results, but I know Rust-Oleum is a good product. Hope I am not disappointed.

I am now about to paint the front and rear plastic bumper pieces. The back is flat and easy to prep and paint, but the front has all sorts of nooks and crannies. My question is, do I have to sand every single inch, every single nook and cranny on the bumper before painting or can I just clean it very well, maybe use an adhesion promoter, then primer, then paint?

The area I'm talking about in the picture is the grill work below where the license plate mounts.

And I have sourced a bumper that is in much better shape than this one.

 

[MSGGrunt]

The more I research the more opinions I find, when painting plastics that is. My plan of attack is this. Sand everything with 420 grit as well as I can. Clean and tack rag. Spray an adhesion promoter. Paint with Rustoleum Plastic paint. Let dry thjoroughly. Wet sand with 800 grit and then three or four coats of Dupli-Color clear coat. Opinions welcome.

 

[toyyota]

I would always use one brand of product. Use Dupli-Color adhesion promoter, color coat, and clear coat. There will be less chance of a bad reaction and a better set of instructions from the manufacturer. Adhesion promoter is not needed on a lot of plastics, but wont harm the repair either way. Normally a light "tac" coat of promoter on raw plastic is all that is needed, painted plastic can be painted without it, if you don't have any bare plastic.

 

[se2000]

Does the clear coat have modifiers in it for flexibility? If not, it will crack and maybe fall off,especially on a bumper.

 

[JCruse]

I haven't tried it yet but SEM makes this for areas that can't be sanded.

Softens the substrate promoting adhesion on difficult to sand areas.
Ahesion promoter for ABS, PVC, and similar substrates

 

[MSGGrunt]

So, the SEM Sand Free is designed for areas where sanding isn't practical? This may be the same thing as adhesion promoter, but SEM is more than likely a higher quality product than say Rust Oleum or Dupli-Color adhesion promoters. Does anyone have first hand experience with this? The area that I am concerned with making sure there is a good bond for the paint is all the nooks and crannies in the front bumper. I assume just like the SEM can says, this is designed for just these places?