Corrosion protection: how to keep rust away from the body
Zinc primer, undercarriage treatment and cavity wax — and the thinking behind corrosion classes
A paint job is not just cosmetics. Under the color lies a system whose primary job is to keep moisture and salt away from the raw metal. If it fails rust works on under the surface long before it becomes visible — and when it's finally seen the damage is typically worse than it looks.
§Where does rust first appear?
Rust rarely sets in the middle of a flat, well-painted sheet. It finds the weak points: places where the paint is broken, or where moisture can collect without being able to escape again.
- 01Stone marks and scratches where the paint/coating is broken right down to the metal
- 02Joints, seams and welds where there are cracks and sharp edges
- 03The undercarriage exposed to rocks salt and moisture from the road.
- 04Cavities in door bottoms, thresholds, and door frames where water can stand
§Corrosion protective products
| Product | Function | Typical placement |
|---|---|---|
| Zinc or epoxy primers | Binds to the exposed metal and inhibits corrosion before topcoat is applied | Exposed sheet after sanding |
| Undercarriage treatment. | Strong, wear-resistant protection against stones and salt water | Undercarriage and wheel wells. |
| Cavity wax | Creeping wax that penetrates narrow cavities and displaces moisture | Door frames, thresholds, backsplashes. |
§Standards and the thinking behind corrosion classes
Within standard
Passenger cars are not directly covered by this standard, but the same systematic thinking — how aggressive is the environment and how long should the protection last — recurs when assessing how strong an undercar treatment a car driving on salted roads every winter really needs. Precisely knowledge of this type of industrial surface treatment is included in the training's competence objectives, where the apprentice should be able to identify different types of industrial surface treatment with associated safety measures, materials and methods.
“Rust never works on breaks. The best corrosion protection is the one that is applied before you can see that it was needed.”