"Liquid Sandpaper"

1MeanA said
I would just sand it...180 grit for primer and 400-600 grit for paint. The SEM TDS says its an adhesion promoter for plastics.

Whoops, I linked the wrong product. I meant to link to one for metal.

Bodyperson said
Most of the body shops around here us a product called Bulldog. Expensive and super stinky. Use it for things like chrome or glass or like under a cab or something.

340six said
I use Bulldog. Works well if ya have plastics or need to blend. Dying plastics or vinyl tops too.
Not cheap but Works. My wife had some plastic garden pots she wanted another color. I cleaned and shot with Bulldog then paint. Look like new 3-4 years later.
Wear real paint protection. A real respirator many skip it for small jobs , primers and prep.

Bulldog, okay. I probably will sand, though. But I keep getting ahead of myself. I'm not a painter, and I haven't found one yet for this job. I'll do what he prefers; or maybe wants to do it himself. I'll mention Bulldog.