Undercarriage coatings: Rustproofing your vehicle

Rust: an inevitable inconvenience. Although you can’t prevent rust from forming on your car ultimately, you can slow down how fast it spreads with rustproofing measures, including undercarriage coatings.

Let’s review how to protect your car’s undercarriage from rust build-up and some other tips for keeping rust at bay.

What is an undercarriage coating?

An undercarriage coating, or undercoating, is a protective, rustproof layer that keeps salt, dirt, and grime from lingering on the exposed metal underneath your vehicle.

The term “rustproofing” refers to the application of a protective wax to areas like the fenders, tailgate, and body panels. Undercoating can fall under the category of rustproofing, but it specifically targets the undercarriage and provides a more in-depth layer of protection.

Types of undercoating

Originally, undercoating was done by spraying used motor oil on the undercarriage. Now, we have a wide range of undercoating products to choose from that follow the intentions of the motor oil method (to slow down rust).

The most common types of undercoating products are:

• Rubberized: Most popular type. Dries to a soft, rubber finish. Works best on new, rust-free surfaces.
• Polyurethane sealant: Comes in a spray canister. Offers a paint-like finish and is great at fighting corrosion.
• Wax or paraffin-based: This is the most affordable option. It doesn’t fully dry but provides a moist barrier to fight corrosion.
• Oil-based: This method works well on an already rusted surface and can be applied anywhere, but it doesn’t last as long as other methods.
• Asphalt-based: A heavy-duty option best for trucks and machinery. Longer curing time and not paintable.

Keep in mind that undercoating doesn’t treat existing rust. Whatever method you use, start by eliminating as much rust as possible.

When and how to apply undercoating

The way you apply undercoating will depend on which method you use. For example, asphalt-based and rubberized coatings are best left to professionals, whereas oil-based and wax/paraffin-based products can be DIYed. Each method has specific requirements to ensure proper application.

Depending on the type, undercoating needs to be reapplied every one to three years. The best time to apply is in the spring or summer, when the weather is warm and dry. Rust is most common in the winter, so it’s important that your undercoating is set well before then.

Undercoating cost

DIY undercoating may cost about $100 to $150 (depending on the size of your car/how much product you need). For a professional undercoating, you can expect to pay anywhere from $300 to $1,000 (the higher end will be at a dealership). Although you can save money DIYing your undercoating, a professional service will guarantee it’s done right to offer you the best layer of rust protection. Many professional services also offer a limited warranty on their rustproofing and undercoating.

Contact your local NAPA AUTOPRO service centre to determine if they offer undercoating.

Although undercoating can be costly and time-consuming to apply, the benefits of protecting your car from rust build-up and other damage are often worth it.

More rust-prevention tips

Other ways to prevent rust from building up (on any part of your vehicle) include:

• Wash your car every two to four weeks, especially in the winter. Don’t forget the undercarriage!
• Rustproof other parts of your car with rust inhibitor and wax.
• Touch up stone chips and repair dents as soon as you notice them.
• Park under shelter whenever possible.

Photo: iStock-2035732783