Easy Steps on How to Undercoat a Car

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Dealing with rust is a losing battle, and we’re talking about the underbody in your car. Quite frankly, metal components have zero to little chance of battling rust and corrosion. Exposing bare metal to salt, air, and water only leads to dire consequences. Luckily for you, new cars are pre-treated with rustproofing or undercoating from the factory.

Like all businesses, auto manufacturers don’t like getting sued, and companies, in particular, are now extremely conscious of product quality. But have you ever wondered how long factory-applied rustproofing or undercoating lasts? And the bigger question is, should you do something about it as your car gets older or is out of warranty?

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Professional undercoating is not cheap, but we’re here to help. Here are the easy steps on how to undercoat a car.

DIY Vehicle Undercoating: Materials Needed

First, you’ll need a way to hoist your vehicle in the air or raise the body for a couple of feet at the very least. It’s possible to do this with jacks and jack stands alone, although safety should be your primary concern. Never get under a vehicle unless it’s supported by jack stands or a lift.

Materials required:

  • Pressure washer (or a garden hose with strong water pressure will suffice)
  • Undercoating spray (or a separate spray gun with undercoating solution)
  • Microfiber towels
  • Gloves, masks, and eye protection
  • Tire wrench
  • Old newspapers and masking tape (optional)

How to Undercoat a Car: 7 Easy Steps

Step 1:

Raise the vehicle using jack stands or a lift. After the vehicle is secure, the first real step is to blast the underside of the vehicle with clean water. In this step, you can use a garden hose with strong water pressure, although having a pressure washer is the best way to go.

The idea is to rid the underbody of excess grime, dirt, mud, salt, and other debris. If you find grease or any other hard-to-remove contaminant, you may need to wash the underbody with degreaser and plenty of water.

If you don’t have a lift, jack up the vehicle, remove the wheel nuts, and remove each wheel before supporting each side of the car with jack stands. Removing the wheels will make the job easier and prevent overspray on wheels and tires. If you have access to a lift, you can choose not to remove the wheels and tires.

Step 2:

Allow the underbody to dry thoroughly. In this step, you can grab a couple of shop towels or microfiber rags and wipe each section of the undercarriage to dry. You can also use pressurized air to accelerate the drying process.

Again, the idea is NOT to apply undercoat on a wet surface.

Step 3:

While waiting for the underbody to dry, now is a good time to inspect the surface for rust damage. Remember, if the damage is extensive (or if you see more rust than actual metal), no amount of rustproofing or undercoating will solve the problem.

But if the problem is minor, you can go ahead and treat each corroded section with rust-stopping spray paint ( like Rust-Oleum Stops Rust Protective Enamel) or a water-based rust converter (like Corroseal Water-Based Rust Converter Metal Primer). Out of the two products, we particularly like Corroseal. It paints, primes, and converts rust in one step. You can also apply the product using a brush, roll, or spray.

We’re not saying you can’t proceed with the undercoating unless you pre-treat the surface with a metal primer or any sort of rust converting spray. But it’s best to eliminate rust from the source instead of covering the damage with undercoating. While it’s true the undercoating solution is strong enough to combat and prevent rust, it’s always best to start with a clean and prepped surface that is free of rust.

Step 4:

After treating severely damaged parts with rust converter, it’s a good idea to cover specific areas of the undercarriage with an old newspaper and some masking tape. This helps prevent overspray. Remember, it’s best to avoid spraying the following components with undercoating:

  • Muffler/exhaust
  • Exhaust heat shield
  • Driveshaft
  • Transmission
  • Engine
  • Brake rotors
  • Differential
  • Spare tire

In some cases, removing the spare tire from the underbody is necessary. You can spray undercoating on some rubberized and metal lines under the chassis but avoid spraying on the above-mentioned components to prevent fires and accidents as you drive the vehicle.

Step 5:

After all the prep work, it’s now time to apply the undercoating. One of our favorites is the 3M Professional Grade Rubberized Undercoating. It comes in a handy spray can and has both rust prevention and sound deadening properties to reduce road noise.

But if you have a spray gun, we like using Rusfre Spray-On Rubberized Undercoating. Both products are easy to apply and are soft and rubbery when fully dry.

First, put on your protective gear including gloves and a face mask. It’s also a good idea to wear a painter’s suit with a hood if you need to literally crawl or lie down to spray the undercoating.

Next, spray the undercoating and move slowly from side to side to ensure even coverage. You can apply the undercoating to all parts of the undercarriage except for the components listed above. This means it’s safe to apply undercoat to the wheel wells and under the fenders. If you’re using petroleum or tar-based undercoating, you can apply the product using a basic paintbrush.

Step 6:

After applying the first coat, allow the product to dry before applying a second coat. You can apply up to three coats if you prefer, but it’s more important to follow instructions printed in the can or bottle. Generally, you should apply multiple coats to ensure long-term rust and corrosion protection.

Step 7:

Allow the undercoat to fully dry in an hour or so and you’re done!

Conclusion

You’ll save a ton of money on DIY vehicle undercoating. All you need are the right materials and the right technique.

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Jose A. Brown
 

Jose A. Brown is a mechanic engineer and an enthusiastic blogger whose mission is to provide the readers with the best tips, guides in the Home Improvement, DIY Project, and Industry.

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