Car and Underbody Rust Protection

These two products serve different purposes. Cavity wax is designed for internal use, such as inside door panels, sills, and chassis rails. It is thin enough to creep into seams and joints to displace moisture and prevent rust from the inside out. Underbody coating, by contrast, is much thicker and more durable. It is designed for external use on the underside of the vehicle to resist stone chips, road debris, and salt, providing a tough, abrasion resistant barrier that stays in place even in harsh conditions.

Yes, loose or flaky rust must be removed before you apply any protective coating. Applying a barrier over loose rust will simply trap moisture against the metal, which can accelerate the corrosion process. We recommend using a wire brush or abrasive disc to remove all loose material. If there is stubborn surface rust remaining, consider treating the area with a chemical rust converter first to neutralise the oxidation before applying your wax or underbody sealer.

In many cases, yes. If your existing underbody protection is still sound and firmly attached, you can often apply a fresh coat over the top to refresh the barrier. However, if the old coating is brittle, cracking, or lifting, it must be removed first. Always ensure the surface is clean, dry, and free from new dirt or road grime before applying a fresh layer, as the new product needs a clean surface to bond correctly.