Scratches can damage car rust proofing on the exterior of your car. Rust proofing is an encapsulating product that is relatively easy to scratch. If this happens, the scratch can actually expand and damage a larger area of the rust proofing. If something scratches the car where the rust proof is, you should most likely apply another coating of it. This is a relatively easy process that can make a big difference in the long-term performance of your car. You need to make sure that the undercarriage of the car is protected at all times.