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How to Undercoat A Car

The clean, rust-free undercarriage of a small car.

The road is a filthy place. It’s not only exposed to the elements 24/7, it’s also covered in what we use to clear away those elements (like salt and cinders for snow removal) as well as all the debris from vehicles, like leaking fluids and microscopic bits of worn tire.

Your vehicle needs protection from all of this. Here we will discuss how to undercoat a car to protect it from wear and tear while you’re on the road.

Do I Really Need Undercoating?Undercarriage of a vehicle

Yes. Corrosion is bad enough for the parts of your car that you can see easily, but it can also affect internal components. All that gunk that kicks up from your tires can trap moisture on your undercarriage and lead to rust, and if you live in a state that uses salt for snow removal, the corrosive mixture of water and salt can wreak havoc on bare metal components.

Types of Coating

There are three common types of undercoating products, distinguished by their primary ingredients:

  • Polyurethane: The biggest upside to polyurethane undercoating is that it fills in cracks you might not even be able to see, pushing out salt and moisture in the process. This type of undercoating even inhibits corrosion on a pretty aggressive level. The downside is the extensive prep time required to do the job right.
  • Rubberized: The benefit to this undercoating is right there in the name, rubber. This undercoating is a bit softer, which allows some debris to bounce off instead of causing dents or nicks where rust can get a foothold. As a result, it’s one of the most popular ways to undercoat a car.
  • Paraffin or wax-based: This is an inexpensive and easy way to get the job done. Like polyurethane, this option fills cracks and crevices to provide protection for those hard-to-see places. If there’s a downside, it’s durability. These aren’t do-it-once-and-forget-it undercoatings, and you’ll probably have to reapply paraffin or wax-based undercoatings every year.

Tips for Prep and Application

Is this a DIY job, or should you hire a pro to undercoat a car? In most cases, this is something you can do yourself if you have a modicum of experience with working on cars or if you’re handy around the house.

Plan on this job taking a weekend. Remember that the most important and most time-consuming step is careful preparation. You don’t want to trap corrosion-causing material up against the bare metal of your undercarriage, as it will continue to do damage that you won’t be able to see.

Begin by brushing or grinding off any rust that’s already there — yes, all of it — and then apply paint or primer to those freshly de-rusted areas. Once the primer has dried, follow the manufacturer recommendations for the undercoating you’ve chosen. Just like painting and bodywork, this is not a job to rush. Doing research and taking your time will pay dividends here.

While it can be a laborious and time-intensive job, learning how to undercoat a car can add years to the life of your vehicle, increasing its utility to you and raising its resale value.

Check out all the undercoating products available on NAPA Online, or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on undercoating your vehicle, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Mike Hagerty.

Mike Hagerty View All

Mike Hagerty is an automotive journalist whose work has been featured on radio, TV, in print and online since 1997. He's the Publisher and Editor of, and contributes car reviews to the Los Altos Town Crier and Previous outlets have included KFBK and in Sacramento, California, the ABC television affiliates and Hearst-Argyle and Emmis radio stations in Phoenix, Arizona; AAA magazines for Arizona, Oklahoma, Northwest Ohio, South Dakota and the Mountain West and

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