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Undercoating: The Good, The Bad, and The Rusty

Undercoating: The Good, The Bad, and The Rusty

We usually write blogs to our entire audience – but this one is truly a northern-focused article. So, if you live south of cold-weather winters, you’re likely going to be like – WTF is Timmah talking about? Today we’re going to discuss undercoating products. And for those who deal with arctic climates or live in areas that frequently use road salt or mag chloride, it can be a lifesaver to protect the undercarriage of your daily driver.

The question we need to address though is whether these products are still needed. It’s no mystery that cars made in the past were made from hard steel and durable metals, that were prone to oxidation and eventually – the development of rust. But road warriors of today are constructed from aluminum, polycarbonate materials, and other exotic materials that are less susceptible to contaminants.

So, let’s discuss automotive undercoatings. In today’s AvalonKing article, we’ll break down the good, the bad, and the ugly about today’s undercoating solutions. We’ll explain what they are, how they work, the pros and cons of using them, and whether it is needed at all. We will also introduce a few of the best products on the market today.

What is an Undercoating?

If you live in the Northern USA or in coastal regions like Houston, Louisiana, and other cities, it’s quite possible you’ve been introduced to the term undercoating. These ‘aftermarket’ dealership add-on options are typically applied at the factory or the dealership and are intended to provide a protective layer for the undercarriage.

The undercoating is sprayed on the chassis and is marketed and advertised to customers as a rust protectant that also helps reduce road noise. It’s always best to apply an undercoating when you first purchase a new car, as it coats to the surface and not road grime or other ‘stuff’.

What is the Difference Between Undercoating and Rust Proofing?

You’ll typically hear these two terms used to basically describe the same concept – but they are different. They are both intended to protect the vehicle from corrosion and developing rust. An undercoating is a sprayed-on accessory, that protects the materials underneath the vehicle.

Rustproofing is a process that involves the application of protective waxes or other coatings on other areas that are made of corrosion-prone materials on the outside of the vehicle. Some of the common areas that are ‘rust proofed’ include fenders, upper body panels, weld points, tailgates, and rocker panels.

There is another ‘term’ that can be confusing to consumers – and that’s rust protection. Rust protection is a manufacturing process that adds ingredients that acts as a rust-inhibitor. A rust inhibitor helps to block the circulation of electrical current – which is a critical component in the development of rust.

To be honest, most cars, trucks, and SUV’s made today have some rust protection ingredients mixed into the materials. Plus, more and more daily drivers are using materials like Aluminum that naturally resist the development of rust.

What are the Different Types of Undercoating?

If you’re considering the investment in an undercoating, you’ll have a few options to consider. Now, to be clear, if you’re opting for the dealer-installed – you’ll likely not have a choice, as dealers have their own preferred methods. Here are the different methods for applying undercoating products.

Spray

The most common method of dealer-applied undercoating is via the spray. The coating itself is a tar-like substance that ‘sticks’ to the undercarriage components and acts as a barrier to resist salt, moisture, oxygen, and other items that lead to corrosion. Undercoating spray can be purchased as a DIY product, but it’s tricky to apply – so it’s best to use this method at the dealership on a new vehicle.

Electronic

This method involves removing the electrical current capacity of items underneath the vehicle. It circulates a weak electrical current through the materials, which reduces the potential of corrosion. The electronic method of undercoating is completed by a professional, not a DIY solution.

Drip Oil Spray

When DIY’ers consider applying an undercoating, this is the method of choice. Drip oil spray is an incredibly messy, but very effective method of protecting the undercarriage. When it’s sprayed, it fills all the nooks and crannies of the chassis, providing an exceptional layer of protection. The problem is it takes a long time to cure. In fact, it’ll continue to drip for a minimum of 48 hours in most cases, and not fully cure for up to a week.

Dripless Oil Spray

The final option is dripless oil spray. This is a wax-like substance that will be applied to the entire vehicle (body and undercarriage) to provide a rather strong layer of protection but can wear thin sooner than other traditional methods.

How Does Undercoating Protect from Rust?

A few weeks ago, we wrote an article about rust protection and how ceramic coatings help reduce the potential of rust build-up. In that article, we outlined the science behind what causes rust. For purposes of answering this question, it’s important to revisit that article.

“When iron or steel rusts, it’s an example of corrosion – which is an electrochemical process that involves the combination of an anode (which is a piece of metal that gives up electrons like a dude making it rain at a strip club), an electrolyte (a liquid that helps move those electrons – not the same stuff found in sports drinks), and a cathode (which is the piece of metal that accepts electrons – like that aforementioned stripper on the pole).”

Tim Charlet – Rust Corrosion and Ceramic Coatings on AvalonKing.com

When metal corrodes, electrolytes supply the fuel (or oxygen in this case) to the anode. As oxygen is introduced to the metal, electrons are freed. As they move to the cathode, metal on the anode vanishes and is converted into rust.

An undercoating is intended to block a few of the contributing factors that lead to corrosion.

Coatings

The coating solutions will block the electrolyte from penetrating the metallic surfaces. In most cases, this is either road salt, saltwater, or standard wastewater on the roads. Most undercoating products last for multiple years, with some of the offering a ‘lifetime’ warranty against corrosion.

Electrical Method

The electrical method explained above helps to block the anode from circulating electrons. The material is exposed to salt, water, and other electrolytes, but if the metal is negatively charged, it can’t move the electrons to the cathode, and thus – corrosion can’t occur. This is typically a permanent solution that does not need to be repeated. It’s also the most expensive one.

What are the Pros and Cons of Having Undercoating Applied?

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Although most new cars, trucks, and SUV’s are quite well protected underneath, for those living in cold-weather regions or areas where saltwater is common, having an undercoating applied at the dealership is a smart investment. In most cases, it’ll only run you a few hundred dollars and is well worth the investment – especially if you’re going to keep your ride for more than five years.

Here are some pros to applying an undercoating:

Extends Vehicle Lifespan

The biggest advantage of undercoating products is the protection against corrosion for longer periods of time. Most of them can last for up to 10 years or more, which helps reduce rust and thus extends the lifespan of your vehicle.

Reduces Road Noise

An extra layer of insulation is always a good way to reduce noise from penetrating materials. Whether it’s a home or your car, the more ‘padding’ between you and the source of the noise, the quieter things will be naturally. An undercoating serves as this purpose for cars, trucks, and SUV. So, if road noise is something that bothers you, consider this option.

The only “con” of an undercoating or rustproofing sprays is the cost. However, when you weigh the cost of replacing a vehicle due to rust damage vs the few hundred dollars for a professional to coat your vehicle, it really is a no brainer.

How to Apply a DIY Undercoating or Rust Proofing Spray

So – you’re thinking, “well – shit, I can do it myself”, you’re correct. There are several DIY products for applying a rustproofing or prevention spray on the undercarriage of your ride. However, it can get messy, cause your vehicle to be out of service for a few days while it cures, and is usually more time-excessive vs the amount of money to have a pro take care of it for you.

But, if it floats your boat, here are some tips on how to apply these products. Remember, each type of underbody spray is unique, so it will require specific steps to be completed. Please check with the manufacturer before proceeding and follow their exact methods.

Materials and Supplies You’ll Need

Applying an undercoating starts with removing all debris and contaminants underneath the vehicle. To accomplish this, you’ll need some supplies including:

  • Degreaser products
  • A disc grinder and pads
  • Air hose
  • Eye protection
  • Protective gloves
  • Sandpaper (usually 200 grit)
  • Scraper
  • The Undercoating & Recommended application products
  • A hydraulic lift (quite helpful for removal and spraying)

Here are the general steps for applying a DIY undercoating.

Step One – Cleaning the Underbody

This is an example of how NOT to prep for an undercoating. It’s great for routine maintenance, just not for prepping to apply these products.

The first thing you need to do is fully debris the undercarriage or all areas you intend on treating with the spray. To do this correctly, you’ll need a hydraulic hoist or lift. Here are the general steps for cleaning:

  • Degreaser. Use a high-quality, commercial-grade degreaser to remove all the grime and oils under the vehicle. It’s best to follow the exact steps as recommended by the product manufacturer. Generally, spray, let it soak for a few minutes, then remove with shop rags or microfiber towels you don’t mind trashing.
  • Grinding: The next step is to grind any existing rust or hard contaminants from the chassis or areas you want to treat. It’s a good idea to use a mild grinding pad and take a progressive approach to removal. Always use Eye Protection!
  • Sanding: After all the crap is off the surface, use a 200 to 400 grit sandpaper to remove scratches and other small contaminants.
  • Use a Tack Rag to IPA solution: Once all debris has been removed, complete the prep process by wiping down the area with a tack rag or IPA solution.

Priming

Most of the undercoating products for DIY consumers require a primer, which serves as the basecoat. Always follow the instructions of the manufacturer for optimal results. The best type of primers is those with high zinc levels, as this really helps to reduce that whole corrosion process if the surface layer is penetrated.

Undercoating

Many undercarriage sprays are similar to spray bed liners

The final step is applying the undercoating itself. Most of the products involve a two-step or dual-layer spray. The first coating should be a rather thin coverage, mainly to coat the entire surface area. You should allow at least an hour for the first layer to tack – especially if you’re using a rubberized type of undercoating.

The second layer of the spray should be applied liberally. Again, it’s important to follow the steps recommended by the manufacturer of the product you use. Curing will vary from a few hours to a few days.

When you’re finished with the process, the undercarriage should be well protected from saltwater, mag chloride, road grime, and other contaminants that cause oxidation and corrosion to occur.

What is the Best Way to Protect Surface Materials from Corrosion?

There are some rust-proofing sprays that are simple to spray and apply, they usually only last about a year – or the same as a paint sealant. If you’re looking for a longer-lasting solution, that can be applied to body panels, plastic materials, headlights, vinyl, and PPF – a DIY ceramic coating will do the trick.

An automotive ceramic coating is a highly-concentrated liquid polymer that is primarily formulated with liquid Quartz (or SiO2 – silica dioxide). When the coating is applied, it seeps into the clear coat or the porous surface and then creates an exceptionally flat and superhydrophobic surface.

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The coating then cures, creating a semi-permanent and extremely strong layer of protection that blocks UV rays from penetrating to the clear coat and most importantly, the paint surface itself. It’s completely transparent, so it amplifies the natural color brilliance of your automotive paint; while blocking electrolytes from penetrating to bare metal – and thus, reducing the potential of corrosion.

Wrapping it Up

Rust protection is a real thing for people living in cold climates or who live in coastal communities. Having a car treated with an undercoating is a very smart way to reduce the build-up of corrosion and extend the lifespan of your vehicle. However, if you’re going to coat the undercarriage, don’t forget about the other 80% of your car.

A ceramic coating is a great way to extend life, protect the shine, and keep the surface of your car cleaner, for longer periods. Investing in a high-quality DIY ceramic coating like Armor Shield IX is a great way to ensure corrosion doesn’t turn your ride into a rust-bucket.

If you enjoyed this article, then you'll love AvalonKing's automotive care products for Do-It-Yourselfers. We create "No B.S products" for an affordable price. And the best part, we treat our customers like family, so if you have any questions or just looking to chat about cars, we're only an email or call away. Check out our homepage here.

Tim Charlet

Tim is part of the AvalonKing team as a content editor. A 30-year automotive guru, marketing super freak, and accomplished publicist & columnist, “Timmah” is also a licensed NHRA Drag Racer, a proud dad of two, and loves a good Guinness two-part pour.
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These are our recommended quantities for the respective type of vehicle. The Volume Savings can be seen besides/below.

Type of Vehicle Recommended Quantity Volume Savings
motorcycle   Motorcycle 1 bottle*
small car   Small car 1 bottle*
sedan   Sedan 2 bottles* Save $35 (25%)
pick-up truck   Pick-up 2 bottles* Save $35 (25%)
jeep   Jeep 2 bottles* Save $35 (25%)
suv   SUV 3 bottles* Save $70 (33%)
van   VAN 3 bottles* Save $70 (33%)
boat   Boat 4 bottles+* Save $110 (39%)

*Please note that it may be a good idea getting an extra bottle, ensuring you don't run out when doing an application.

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