Enhance the appearance of an exterior door jamb by refinishing it with paint. If the trim is made of plastic, employ specific preparation techniques to condition it for its new finish. Plastic is a slick, nonporous surface that does not accept adhesion well. Abrade the door trim, using friction-based sanding techniques, or the new finish will rapidly flake. Choose a particular finish coat manufactured to stand up against harsh weather conditions and fluctuating temperatures.
Clean the plastic exterior door trim with a plain dish soap, using a coarse sponge. Rinse the trim with wet rags and thoroughly dry it with towels.
Abrade the door trim to promote adhesion. Sand the exterior plastic with 180-grit sandpaper until it feels slightly coarse.
Protect areas next to and beneath the exterior door trim by covering them with masking paper and blue professional painter's tape.
Coat the abraded exterior plastic with acrylic latex primer, using a two-to-three inch polyester brush. Brush vertically. Apply a light coating, using gentle pressure. Allow the door trim to dry for two hours.
Wash all of the primer from the brush, using fresh water.
Coat the primed exterior plastic with acrylic latex paint, using the polyester brush. Brush vertically. Apply a light coating, using gentle pressure. Allow the door trim to dry for two hours.
A polyester brush is appropriate for painting smooth plastic trim. Don't use a nylon brush, or the finish will dry with flaws. Do not paint unprimed plastic exterior door trim, or the finish will flake. Do not prime unsanded, plastic door trim, or it will reject the primer base coat.