The main body of the car's rear bumper - the role of the primer coating
The core functions of the base coat on the rear bumper of a car are as follows:
Corrosion and rust prevention: Even though the bumper is mostly made of plastic, its frame or some high-end models' bumpers may contain metal components. The base coat can effectively prevent moisture, salt, acids, bases, and other corrosive substances from penetrating, protecting the metal structure from oxidation.
Enhanced adhesion: The base coat firmly adheres to the surface of the bumper (whether it is plastic or metal), providing a solid foundation for the subsequent color coat and clear coat, preventing the paint from peeling off or chipping.
Filling minor defects: It can fill in minor scratches, pores, or unevenness on the bumper surface, making the subsequent sprayed paint surface smoother and more uniform.
Improving the overall performance of the paint film: Increasing the coating thickness, improving the fullness and gloss of the paint surface; some base coats also have properties such as resistance to stone impact, chemical resistance, and flexibility, enhancing the durability of the bumper.
Adaptation to the original factory process: Many original factory bumpers are shipped in a "bare base coat" state, facilitating subsequent matching color coating based on the vehicle color, while balancing production flexibility and paint surface consistency.
Note: If the base coat of the bumper is damaged (such as scratches revealing a gray or white layer), it should be repaired promptly; otherwise, the metal components are prone to rust, and the subsequent painting adhesion will be affected.
It is recommended to undergo a complete repair process of grinding, reapplying the base coat, and then painting the color coat and clear coat at a professional repair shop.
When a rear bumper of a car has a "base coat failure", it usually refers to the exposure of the paint surface due to damage, such as scratches, scraping, or aging. Since modern car bumpers are mostly made of plastic (such as PP or ABS), unlike metal bodies, they do not rust like metal, but long-term exposure may accelerate aging or affect appearance due to ultraviolet rays, rain, dust, etc.
Is repair necessary?
Minor scratches (not affecting the base coat): They can be left untreated or lightly polished with toothpaste or polishing wax to restore the shine.
Base coat exposed but with a small area (diameter < 2 cm, length < 5 cm): It is recommended to use a "repair pen" or "repair wax" to cover it, preventing further deterioration.
Large areas of base coat exposure, obvious depressions, or deep scratches: It is recommended to go to a professional repair institution for local painting or full-piece repair.
Recommended treatment method
Small area damage (self-treatment)
Clean the damaged area to ensure there is no oil stains or water marks.
Use a "repair pen" or "repair wax" that matches the vehicle paint color, apply it evenly along the scratch direction.
Allow it to dry for 24 hours, then use 2000-mesh fine sandpaper to gently sand, and then polish and wax.
Moderate to severe damage (professional treatment)
Go to a 4S store or professional auto repair shop, use spot repair or full-piece painting.
The professional process includes: cleaning → grinding → optional atomic filler → base coat → color coat → clear coat → baking for curing.
Using a baking oven can significantly enhance adhesion and durability.
Temporary emergency solution
If repair is temporarily impossible, apply "transparent nail polish" or "special plastic protectant" to slow down environmental erosion.
Important notes
Plastic bumpers do not need to worry about rust; however, if not treated for a long time, it may cause the paint surface to peel off, the base coat to powder, and increase the difficulty of subsequent repair.
After repair, avoid rain or washing the car for at least 3 days to ensure the paint film is fully cured.
If the vehicle is still within the warranty period and it is confirmed to be non-human paint surface peeling (such as blistering, peeling), contact the 4S store to assess whether it is a quality issue.
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