Underseal
Underseal is a thick, resilient coating applied to concrete, and 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.
On vehicles
Historically, a bitumen-based compound was used, but after approximately a decade, such coatings become brittle, and water can become trapped between the underseal and body metal, counterproductively creating a more favourable environment for rust than if no underseal were applied at all. Wax-based underseals do not have this disadvantage, but can be eroded and eventually washed if a pressure washer is used to clean the vehicle's underbody. Rubber-based underseals are also sometimes used.Vehicles for sale in some territories are not undersealed, because the climate is not sufficiently aggressive to warrant it. If such a vehicle is subsequently imported into a country with some combination of high rainfall, cold winters, and salting of roads to prevent ice, application of underseal is often used.