Things You'll Need
320- to 400-grit sandpaper
Block or belt sander
Air blower or hair dryer
Polypropylene spray paint
Polypropylene is a type of thermoplastic polymer used on boats, cars, models and other manufactured goods. If you want to change the color of the polypropylene, you'll have to do more than just slap a coat of paint on its surface. Because it is often quite smooth and nonporous, most paints have trouble sticking to it. For best results, use a spray paint labeled for use on polypropylene and other plastics. These are available from most major spray paint manufacturers as well as online or at many paint or home improvement centers.
Wash the surface of the polypropylene with soapy water (roughly 1 teaspoon liquid detergent per quart of water).
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Towel the surface dry, then allow it to air dry for roughly 30 minutes.
Put on a dust mask to protect your airway from plastic particles.
Sand the polypropylene surface with a block or belt sander using extra-fine-grit sandpaper. Sand just enough so that the surface of the polypropylene feels rough to the touch. Make sure not to miss any spots.
Blow the sanding dust off the polypropylene with an air blower, or a hair dryer set on high and cool. Wipe the remainder of the dust off with a tack cloth.
Vacuum the sanding dust off the floor with an industrial vacuum. Make sure to get it all. These small particles are easily airborne and will ruin your coat of paint if they settle onto its wet surface.
Put on a pair of rubber gloves and keep them on as you work to avoid transferring the oil from your hands onto the polypropylene.
Moisten, but don't soak, a rag with rubbing alcohol and wipe down the sanded surface. Wait five minutes for the surface to air dry.
Apply a thin coat of paint in smooth, even, back-and-forth strokes. Hold the spray paint can roughly 10 inches away from the polypropylene's surface.
Allow the paint to dry for the amount of time listed on the label.
Repeat Steps 9 and 10 to apply subsequent coats to the polypropylene. Most polypropylene manufacturers recommend four coats of paint for a lasting paint job.
Tape and cover any adjacent parts that you don't want covered in paint.
Make sure that the spray paint's label lists polypropylene as one of the surfaces it covers. Spray paints that are good for most plastics won't necessarily coat polypropylene.
For larger surfaces, skip the spray can and opt for a paint sprayer.