 Underseal

Underseal (often called undercoating in the U.S.) is a thick resilient coating applied to the underbody or chassis of an automobile to protect against impact damage from small stones, which would rapidly chip ordinary paint, allowing rusting to begin.Historically a bitumen-based compound was used, but after approximately a decade this becomes brittle and water can become trapped between the underseal and body metal, counterproductively creating a more favourable environment for rust than if no underseal was applied at all.