Plastic plays a prominent role in the manufacturing of modern vehicles. Over the years, the need to refine aesthetics and reduce vehicle weight to decrease fuel consumption has brought significant changes to car design. Bumpers are now covered with plastic bumper covers that match the shape and colour of the vehicle. Additionally, numerous plastic parts have been added to the body, such as mirrors, spoilers, and various aerodynamic elements. Preparing these parts for painting is very important.

Types of plastics

The first step in preparation is to identify the type of plastic used. This can sometimes seem complicated given the high number of plastic types on a car. There are essentially two families of plastics: thermoplastics and thermosets. Identifying which type is used is relatively simple. Use a coarse abrasive paper such as P80 and sand an inconspicuous section of the part. If dust is generated, it indicates that mechanical adhesion can be created on the part, and primers that are part of the paint film can be applied directly. Conversely, if sanding produces small “balls” of plastic, it indicates that chemical adhesion will be required and that an adhesion promoter must be applied before the primers.

Cleaning the parts

Cleaning the parts is the MOST IMPORTANT step in the preparation process. 65% of issues with paint peeling on repainted plastic parts are caused by improper surface cleaning. The best adhesion promoter cannot adhere to a contaminated surface. The main contaminant is the mould release agent used during its manufacture. Most manufacturers now use a soap-based agent, eliminating the need to heat the part to bring these agents to the surface as was previously required. Check the manufacturer’s recommendations to confirm that heating is not required. Use specially designed cleaners and follow the manufacturer’s procedure. Thoroughly clean the part, ensuring all hard-to-reach areas are covered. Rinse and clean again. Be sure to clean the inner edge of the part to avoid transferring contaminants to the freshly cleaned surface. Using an anti-static gun before applying paint products will greatly help eliminate static on the surface. Using a water- or alcohol-based cleaner will also help dissipate static. The application of primers should be done quickly to prevent airborne contaminants from settling on the surface.

Once preparation is complete

Applying the layers that make up the paint film is the final step in the refinishing process. Respect the film thicknesses recommended by the car manufacturers, especially with driver assistance sensors often present behind bumper covers.