Undercoating involves spraying a tar-based substance on the exposed parts of a vehicle’s underbody. The tar-like undercoating acts as a barrier once it hardens, keeping out moisture, salt, and other substances that could cause rust. Over time rust will cause corrosion and can lead to part failure and a whole host of other issues. Rust is not just ugly but can trigger a number of different system breakdowns, such as leaks that can lead to gradual fuel wasting and even sizable components like the engine and transmission failure. A good undercoating extends the life of your vehicle.