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Is Rustproofing Your Car a Good Idea?


Rustproofing and undercoating your vehicle can protect it from corrosion and rust. This is especially important for the undercarriage of your vehicle, which commonly comes into contact with substances such as water, chemicals such as salt, and other dirt and debris from the road. Without some sort of protection, the bottom of your vehicle can rust and corrode, leading to part failure. Before rustproofing or undercoating your undercarriage, you need to consider a few things.

The advantages and disadvantages of rustproofing/undercoating your vehicle

The best time to rustproof or apply undercoating protection is when you buy a brand new vehicle that hasn't been driven yet. In essence, ask the dealership to apply the protection before you even drive off the lot. For used vehicles, rustproofing could just be a waste of time, as all you are really doing is covering up dirt and grime that already exists on the vehicle.

Apply protection while at the dealership. Many dealerships offer rustproofing or undercoating as an add-on when buying a new car.

This represents the best time to have an undercoating applied, as the underbody of the vehicle is probably the cleanest it will ever be.

If you only plan on keeping the vehicle for a few years, you might consider sparing the expense and foregoing getting an undercoating applied.

Applying an undercoating on a used vehicle. Another option to having an undercoating applied at the dealership is to have one applied at a later time.

This applies most commonly to used vehicles. While the underside of the vehicle has already been exposed to water, dirt, and other debris from the road at this point, applying an undercoating now can protect it from further exposure.

Different types of rustproofing/undercoating

When having your vehicle rustproofed or an undercoating applied, you have a few options to choose from. Whether you prefer the latest technology or a more tried and true method, knowing what the different options are should allow you to choose the best one for your vehicle.

Electronic method. Using a weak electric current, this small device can stop the corroding effects of rust.

You can have these electronic devices installed at the dealership, or save some money and buy them from a source outside of the dealership.

The reviews on these devices are mixed, as this is a virtually new technology.

Undercoating. This method 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.

This undercoating works best when applied to the undercarriage of a new vehicle. It also requires expert application, or it can crack, letting in moisture.

Dripless oil spray. A wax-like substance applied to the entire body of the vehicle, it hardens once it has dried.

One of the downsides of dripless oil sprays is that you need to have holes drilled into the body of the car at specific points to make it effective.

The spray also has a high viscosity, meaning that it does not always get into all of the nooks and crannies of your vehicle.

Drip oil spray. This is the most commonly recommended rust protection.

Drip oil sprays tend to continue to drip once applied until they dry. This dripping can last anywhere up to 48 hours after application.

Unlike the dripless varieties, the more watery nature of drip oil sprays means it gets into more areas on your vehicle, though you still need to have holes drilled in your vehicle's fenders, doors, and other areas to make sure that it gets to all the areas it needs to.

How to apply and remove an undercoating

Materials Needed

While you could pay someone to apply an undercoating to your vehicle, you can also save money by doing it yourself. Before beginning, make sure you have the right equipment to successfully complete the task and enough space to complete the task safely.

Clean the underbody. Start by cleaning the underbody of the vehicle.

This requires you to put the vehicle up on a hoist.

Using a degreaser, clean the underside of the vehicle.

Next, remove all rust from the undercarriage using a grinder. Make sure to wear eye protection when doing so.

Sand any remaining rust using sandpaper designed for metal. You need a sandpaper with a grit of at least 220 or larger.

Wipe away all of the dust created from grinding and sanding.

Paint and prime the underbody. After removing any rust, it is time to prime and paint the underside of the vehicle.

Start by priming all of the areas you cleaned of rust. One of the best primer types to use is a high zinc primer. Allow the primer to dry.

Your next step is to paint over the primer with black automotive paint. Allow the paint to dry.

Undercoat the underbody. The last step in the process requires you to apply an undercoating to the underbody of your vehicle.

Apply the undercoating liberally to the underbody of your vehicle. Make sure to apply it to every part that you expect to be exposed to the road. Allow this coat to dry for at least an hour, or longer if the instructions call for it.

Apply a second coat of undercoating to the bottom of your vehicle. Allow this coat to dry overnight before driving on the road.

  • Tip: Use a rubberized undercoating for best results. A rubberized undercoating is more durable and seals better, protecting the metal from exposure to water.

Removing an undercoating. Removing an undercoating is a simple process.

Spray the undercoating with an undercoating removal spray.

Once the undercoating has been softened enough, use a scraper to remove the undercoating.

While rustproofing is best applied when you first purchase a new vehicle, you can get undercoating protection for your used vehicle to keep it safe from further exposure to water, dirt, and other substances from the road. And while it will not protect your vehicle from rust already on the underbody of your vehicle, you can take steps to halt further corrosion. If you have any questions about whether you should apply an undercoating, ask a mechanic for guidance.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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