Whether you wish to paint your plastic window frames, or you want to shut out light from a room by painting over plastic windowpanes, you must first condition the plastic to accept paint adhesion before you paint, or the finish will flake relatively soon after application. In addition, because plastic is so smooth, you should employ particular application techniques that will work to encourage a professional-looking finish that will not be marred with brushstrokes.
Wash the plastic window with plain washing up liquid using rags. Rinse the plastic with a water hose or wet rags. Dry the plastic window using clean cloth rags.
Enhance the plastic's adhesion capabilities by scouring the surface with a palm sander.
Wipe the plastic with a sticky tack cloth.
Cover areas running adjacent to the outside of the frame with tacky painter's tape.
Apply a thin coat of acrylic primer to the plastic window using a 5 to 7.5 cm (2 to 3 inch) paintbrush. Wait two hours for the window to dry. Open and close the window after one hour to prevent it from sticking.
Wash the brush with plain tap water.
Dilute the acrylic latex paint by mixing in 30 ml (1 fl oz) of tap water per every 4.5 litres (1 gallon) of paint. Apply two light coats of the diluted acrylic paint to the primed plastic window. Allow a minimum of two hours of dry time between each coat, and open and close the window every hour to prevent it from sticking.
Be sure to dilute the paint to encourage a professional-looking finish that will not be marred with brushstrokes. If you are only painting your plastic window frame, use a razor blade to scrape off dried paint overlap from the glass pane.
Don't use plain rags in place of a tack cloth, as this could leave behind dust that may inhibit adhesion.