Plastic is a tricky surface to paint. Unlike wood, plastic is not porous, so the paint has little to stick to. With the right amount of preparation, however, you can paint plastic with success. Keep in mind, however, that depending on the type of paint and plastic you are working with, the paint may eventually chip off, especially after heavy or frequent use.
Clean the item with mild dish soap and warm water. This will remove any surface dirt and reduce the amount of work you have to do in later steps. Use a soft cloth or sponge for smooth surfaces, and a scrubbing brush for textured surfaces (such as patio furniture). Rinse the item with fresh water afterwards, then dry it off.
Lightly buff the surface with 220 to 300-grit sandpaper. Use a light touch and a circular motion to avoid scratches. When you are done, wipe the surface down with a tack cloth.
Wipe down the surface down with rubbing alcohol. This step is very important, as it will remove any oils that might prevent the paint from sticking. If you don't do this, the paint is more likely to chip off later.
Mask off any parts that you do not want to be painted with painter's tape. This would be a good idea even if you will be painting the item with a brush. The masking tape will help give you a clean, defined line between the painted and unpainted areas.
Apply a coat of primer. You’ll need to apply a coat of primer, preferably one that bonds well. This will help even out the surface of the plastic and give the paint something to stick to. The spray-on kind would be the easiest to use, but you can get the brush-on kind as well.
NOW TO PAINT
Set up your workspace. Choose an area with good lighting. Cover your work surface with newspaper or a cheap, plastic, tablecloth. If you will be working with spray paint, it would be best if you work in a well-ventilated area; outside would be best.
Choose a paint that is suitable for plastic. Spray paint works especially well for plastic, but you can use acrylic or enamel/model paint as well. It would be even better if the paint is meant for plastic. Check the label, and look for words such as: "Plastic" or "Multi-Surface."
Prepare the paint, if needed. Some types of paint come ready to use, while others require a little bit of preparation. Before you begin painting, check the label on your can or bottle of paint for any specific instructions.
Apply a light, even coat of paint. Don't worry if the first coat of paint doesn't cover the entire surface; you will be applying several coats of paint. This is important, whether you are spraying or brushing the paint on.
Apply more light coats of paint. Allow each coat of paint to dry before applying the next one. Alternate the directions you paint in for each layer: side-to-side for the first layer, top-to-bottom for the second layer, etc. How many layers you apply depends on the coverage you need. In most cases, you'll only need 2 to 3 coats.
Let the paint to dry completely after your final coat. At this point, your project is complete and ready to use. If you'd like to add some details or a top coat, read on to the next part.
TOUCHING UP AND SEALING THE SURFACE
Fill in any chips or bare patches with a brush. Carefully inspect your piece. If there are any bare patches or chips, fill them in with more paint and a thin brush. If you used spray paint earlier, you might want to use acrylic paint in a matching color and finish for this step.
Add some details, stencils, or weather, if desired. This step is completely optional, but it can bring more life and character to your piece, especially if it is a prop or figurine. Here are some ideas to get you started:
Apply a light coat of polyurethane sealer for extra-durability, if desired. You can use the spray-on or the brush-on kind, but the spray-on kind will give you a smoother finish, however. Apply a single, light coat, then let it dry for at least 30 minutes. Apply one to two more coats, if needed, allowing 30 minutes between each one.
Allow the paint and sealer to dry completely. Just because something feels dry to the touch does not mean that it is dry throughout. Check the label of your paint and sealer bottle, and see if there are any drying or curing times.