It is recommended that the underside of the car, including the inside of the mudguards, be covered with an undercoat to protect against grit and prevent rust,
Applying an undercoat to rusted parts makes no sense; it is a protection against rust, but not a means of preventing rust from progressing.
Rust control can only be achieved by removing the rust from the rusted area and then applying a good coat of paint to which the undercoat is applied as protection.
In addition to its protective function, this underlay also absorbs noise.
Inspect the underbody regularly to ensure that it is not damaged and then update it.
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