Adhesion promoters are a type of clear primer ideal for preparing surfaces like fiberglass, aluminum, vinyl, glass, galvanized metal, chrome and plastic for better paint adhesion. They generally come in a spray can and are fairly easy to apply as long as you avoid the potential pitfalls that many amateur painters fall into.
Clean the surface of the plastic using ordinary dish soap. Rinse the plastic thoroughly. Allow the surface to dry before applying the adhesion promoter.
Spray the adhesion promoter on the plastic. Spray in short intermittent bursts rather than in one steady stream.
Allow the surface to dry for three hours before applying any paint.