Are you riding around in a rust-riddled, corrosion-covered, pitting pile of automotive poo? Have your vehicle’s protective undercoatings given-up the ghost, leaving your car’s tender underbelly exposed to the elements? Sounds like it’s time to apply some undercoating…

On the bright side, if you own a modern automobile, chances are you won’t have to undercoat it all that often. Most cars today are constructed from lightweight, rust-resistant materials like aluminum, plastic, carbon fiber, and magnesium. This not only makes them far more fuel efficient and lightweight, but less susceptible to corrosive contaminants as well.

But that doesn’t mean the modern automobile is immune either, which is precisely why all cars receive an undercoating at the factory, which in colder climates, requires routine cleaning and the occasional reinstallation.

However, a lot of car owners still don’t know what undercoatings are made from, or how they work. Is there more than one kind of undercoating? Are there any health risks associated with this stuff? How often should a vehicle be undercoated?

Well fret no more, because today we’ll be breaking down the good, the bad, and the rusty. As we dissect the latest undercoating solutions, and the pros and cons of this crucial layer of automotive protection.

What is an Undercoating?

Undercoating is sprayed to provide a protective layer for the undercarriage and as a rust protector

If you live in an area of the world that sees a significant amount of snow, or are located in a coastal region, you are probably are already familiar with the term “undercoating.” For everyone else, here’s a quick synopsis…

An undercoating is the first line of defense between an automobile’s metallic underside and the elements, and all vehicles receive a coating of this stuff before rolling off the assembly line. But these OEM coatings will eventually wear-out over time, leaving oil pans, transfer cases, suspension arms, and other metal components vulnerable to corrosion and rust.

Most dealerships offer an additional undercoating as part of a “winter package” option, which typically consists of a “rubberized” media being sprayed across the vehicle’s undercarriage. Once cured, this undercoating has the ability to repel rust and oxidation, rock chips, scratches, and even lower road noise levels.

But even if you purchase for this package option, or opt to tackle an undercoating application on your own, there’s a still a good chance that your vehicle’s underbelly is going to rust. There’s a reason why automotive undercoatings have earned a reputation for being a bit of an unreliable, double-sided sword, and it’s not because they don’t work well.

Quick Tip: It is always best to apply an undercoating when you first purchase a brand-new vehicle, and not a few years down the road. It’s far easier to coat the pristine underbelly of a vehicle with some additional armor, than it is to remove a crap-ton of road grime and gunk.

What’s the Difference Between Undercoating and Rust Proofing?

All you need to know about rust proofing your car

If you’ve ever looked into protecting the underside of your automobile, chances are you’ve come across the terms “rustproofing,” or “rust protection.” Despite sounding identical, there are some key differences between these two methods of rust prevention, even if their intended purpose remains the same.


Rustproofing is a process that involves the application of rubberized sealants, lanolin oils, or any number of other rust-repelling coatings on corrosion-prone surfaces. Some of the common areas that get “rust-proofed” include the undersides of fenders, weld points and seams, fuel tanks, suspension arms, axles, rear differentials, and chassis cradles.

Pretty much any surface underneath the vehicle that does not get hot is fair game when rustproofing, and it is not uncommon to see off-road vehicles sporting this stuff on rocker panels for additional outer protection.

Rust Protection

Rust protection on the other hand, is a manufacturing process that infuses rust-inhibiting chemicals into the components that make-up our automobiles. These rust inhibitors are an engrained countermeasure to the circulation of electrical current, a critical component in the development of rust. These inhibitors are particularly affective at creating a rust resistant surface when paired with resilient materials like aluminum.

Quick Nerd Note: Ever wonder what was in that aerosol can of “rubberized” undercoating? Contrary to their title, these products do not rely upon rubber to protect the belly of your automobile. Instead, they tend to rely upon calcium carbonate (the primary component in eggshells, snail shells, seashells, and pearls), and asphalt to serve their purpose.

What are the Different Methods of Apply Undercoating?

Surface corrosion may be unavoidable, rust build-up can be prevented with a quality automotive undercoating. Photo Credit: FLUID FILM/YouTube
Surface corrosion may be unavoidable, rust build-up can be prevented with a quality automotive undercoating.
Photo Credit: FLUID FILM/YouTube

If you’re considering in having a professional undercoat your car, you’ll need to decide whether to go with a pro installer or a dealership.

While dealer-installed coatings are limited to manufacturer-specific products, privately held service repair shops often have a variety of options to choose from with various pricing plans. Just make sure that the shop is certified and has favorable reviews before committing to an undercoating install.

Regardless as to which direction you choose, the methods used during the undercoating application process tend to be the same across the board. That said, here are a few of the more popular rust repelling products on the market today.

1. Spray-On “Rubberized” Undercoatings

Spraying an automotive undercoating may be time consuming, expensive, and potentially dangerous, but it's your best option for keeping rust and corrosion at bay. Photo Credit: AMMO NYC/YouTube
Spraying an automotive undercoating may be time consuming, expensive, and potentially dangerous, but it’s your best option for keeping rust and corrosion at bay.
Photo Credit: AMMO NYC/YouTube

Perhaps the most common method of undercoating a vehicle, is via the use of a “rubberized” spray-on product. Utilizing a tar-like substance that has been infused with solvents and protectants, spray-on undercoatings stick to whatever they touch.

Once cured they act as a barrier against salt, moisture, oxygen, and any other foreign substance that may lead to rust and corrosion. We’ll delve a bit deeper into the grimy details of what makes these opaque products so popular a bit later.

2. Electronic Rust Inhibitors

A diagram showing how electrical current emanates throughout a vehicle's chassis. Photo Credit: ERPS
A diagram showing how electrical current emanates throughout a vehicle’s chassis.
Photo Credit: ERPS

Electronic rust inhibitors are marketed as a permanent, discreet, easy to install solution to corrosion. It may sound crazy, but this is actually a brilliant idea, if you are able to get it to work.

While the notion of electrical current coursing along the underbelly of a vehicle is undeniably odd, it has been proven to work, but not in the way that one might expect. More on that a bit later as well…

3. Lanolin Wax/Wool Grease

Lanolin coatings are derived from wooly animal glands. Seriously... Photo Credit: FLUID FILM/YouTube
Lanolin coatings are derived from wooly animal glands. Seriously…
Photo Credit: FLUID FILM/YouTube

When choosing an undercoating, the lanolin approach remains a proven, if not slightly unusual rust prevention solution. Commercially, lanolin coatings are used as both a rustproof coating and as a lubricant, with everything from ship hulls and rigging equipment, to heavy-duty excavation machines and production facilities relying upon this water-repelling corrosion inhibitor.

On automobiles, lanolin fills in all of the nooks and crannies of the chassis with a sticky, wax-like substance that’s been derived directly from… sheep glands. It may sound strange, spraying sheep funk across your vehicle’s underbelly, but it really does work.

On the downside, curing times will vary depending upon air temperature and how heavy of a coating has been applied. So be ready for some downtime between car rides after this stuff has been sprayed.

4. Dripless Oil Spray

What Waxy Dripless Undercoating Looks Like Out Side The Container

The final common undercoating option is dripless oil spray. Once allowed to harden on a surface, this wax-like, colorless substance boasts the ability to repel moisture and corrosion for years on end.

Just note that dripless undercoating oil sprays typically require holes to be drilled into the body of the vehicle at specific points in order for the product to penetrate areas that are prone to rusting-out.

How Does Undercoating Protect a Car From Rust?

Intentionally allowing a vehicle to rust may create some interesting aesthetics, but it will also raise a few eyebrows from paint purists and undercoating aficionados. Photo Credit: Micah Wright
Intentionally allowing a vehicle to rust may create some interesting aesthetics, but it will also raise a few eyebrows from paint purists and undercoating aficionados.
Photo Credit: Micah Wright

How Rust Starts

Every year rust gobbles-up billions of dollars in automotive repairs in the United States alone, and 90% of the time road salt and deicers are to blame. These wintry road deicers may make driving a lot safer, but they are also notorious for causing rust to form on automobiles.

Many of the more severe cases of “vehicle rot” are the result of years of contact with magnesium chloride (MgCl₂), or sea salt. Not only is this salty stuff inexpensive, readily available, and an absolute beast when it comes to thawing-out frozen precipitation, it’s also a real bastard for exposed metal surfaces.

When magnesium chloride encounters the right blend of moisture and oxygen, it can cause all kinds of cancerous lesions to form on your vehicle’s exposed underbelly. This led us to draft-up an article that focuses on corrosion prevention, and how ceramic coatings can help reduce the risk of rust build-up.

“Rust formation is kind of like spending quality time with your uncle at the local strip club. For this electro-chemical process to occur, you will need an electrolyte (a big bottle of booze), a cathode (a G-string that’s hungry for attention), and a generous anode (your drunk uncle) who is willing to stuff electrons (cash) into aforementioned cathode.”

A prime example of what happens when corrosion and rust are allowed to fester in the rear quarter panel of an automobile.
A prime example of what happens when corrosion and rust are allowed to fester in the rear quarter panel of an automobile.

How to Prevent Rust From Spreading

Professional rust formation explanation out of the way, we now turn toward the act of interfering with this corrosive molecular catastrophe.

Coat Where the Sun Don’t Shine

Coating solutions are intended to block electrolytes from penetrating metallic surfaces, may it be road salt, acid rain, run-off on the roads, or some other form of liquified sludge.

The trick here, is using a coating that actually works as intended, and then making sure that every square centimeter of your vehicle’s nether regions gets covered. All it takes is one missed spot and ZINGO! You’ve got rust…

What About Electric Shock Therapy?

Utilizing an “electric shock” method, like the one previously mentioned, means relying upon an electrical current to prevent the anode from circulating electrons. The basis here is that if you continuously charge the metal itself with a negative current, it can’t throw electrons the cathode’s direction, thus preventing corrosion from occurring in the first place.

This approach is designed to be a permanent solution, and one that does not need reinstallation or routine servicing. The only issue is that reviews show that it really doesn’t work as well on automobiles as opposed to say, tug boats, and the kits are also quite expensive.

How Long Does an Undercoating Last?

Just one more example of what happens when you don't care for your vehicle's clear coat, undercoating, or any other part of the car for that matter. Photo Credit: Micah Wright
Just one more example of what happens when you don’t care for your vehicle’s clear coat, undercoating, or any other part of the car for that matter. Photo Credit: Micah Wright

Measuring an undercoating’s longevity means factoring-in the environment where the vehicle is being driven, types of deicer and/or salt used on the roads, quality of undercoating utilized, and how thoroughly said coating has been applied. In short, there is no guaranteed timeframe when it comes to automotive undercoating life expectancies. We’ve seen multiple reports of undercoatings only lasting a single winter season, while other drivers have reported a decade of maintenance-free use between coatings.

Quick Tip: Routinely washing the underside of a vehicle goes a long way toward extending the lifespan of an automotive undercoating, especially in environments where road salt is used in winter.

The Pros and Cons of Applying an Automotive Undercoating

Photo Credit: NH Oil Undercoating/YouTube

Although the undersides of new vehicles come shielded straight from the factory, those living in cold-weather regions, or areas along the coastline, may require additional undercoatings. But what are the downsides to this stuff, if any? And does an undercoating’s perks outweigh its cons?

Undercoating Pros

Auto undercoatings tend to be extremely viscous, which helps them double as a form of sound-deadening media. Photo Credit: AMMO NYC/YouTub
Auto undercoatings tend to be extremely viscous, which helps them double as a form of sound-deadening media.
Photo Credit: AMMO NYC/YouTube

The biggest advantage to having an undercoating installed on the underside of an automobile, is knowing that your vehicle is protected from rust and corrosion, to an extent. While there are no guarantees that a rust bubble won’t appear where a rogue rock chip hit your freshly applied coating, most vehicles go years without requiring a touch-up.

Another perk, is that undercoatings add an extra layer of sound-deadening insulation to the underbelly of a vehicle. While it may not be as affective as a dedicated sound-proofing product, and won’t do much when it comes to repelling heat and cold, undercoatings do reduce road noise.

Undercoating Cons

Photo Credit: NH Oil Undercoating

1. Talk About Some Seriously Toxic Stuff!

Like many chemical-rich products, the average undercoating is a gateway to organ failure, cancer, infertility, and genetic defects. After doing a bit of digging, we discovered that quite a few brands don’t even know what this stuff will do to the human body, with some of the more discerning case studies showing that “…25% of the mixture consists of ingredient(s) of unknown acute toxicity.”

So spray safely, and always wear a ventilation mask, protective eyewear, gloves, and a painter’s suit when working with undercoatings.

2. Something Smells B-a-a-a-a-a-a-d

D-a-a-a-a-a-d jokes aside, there’s a reason why Lanolin is called “wool grease.” This waxy substance is derived from a naturally occurring gland secretion found in fluffy animals like sheep.

It is within these hair follicle glands that lanolin exists. A sticky secretion that provides cud-chewing critters like the ultra-fluffy Merino breed of sheep with a waterproof coat that keeps them dry and warm in winter.

On the downside, because lanolin is basically a livestock secretion, it smells sort of like… well… stank-ass sheep glands. This repulsive aroma is even more notable when lanolin is exposed to warmer temperatures too. So if you notice that no one is parking next to you in summer, it might be because they can’t stand the stench of your undercoating.

3. A Not-So Shocking Surprise

Over the years, electronic rust inhibitors have seen a surprising amount of success in both marine and underground structural applications. But as AutoGuide illustrates, the effectiveness of these products depends heavily upon a multitude of factors, many of which are not always present in automobiles.

Most metals do a damn good job of conducting electrical current, which explains why having a module attached to a car battery, with electrodes channeling electricity throughout its frame seems like a brilliant idea… right? Wrong. The following quote explains why this technology doesn’t work well on automobiles.

“Electronic rust protection works, though it’s designed for applications like underground fuel tanks and large boats… in those applications, the metal exterior surface is always wet or damp, allowing the signal to conduct powerfully and fully throughout the metal structure…”


4. The High Price of Vehicle Undercoatings

But perhaps the biggest complaint people have about automotive undercoatings and rustproofing procedures, is how much they cost. This is precisely the reason why many people opt to take matters into their own hands, and attempt to undercoat their automobiles on their own.

How to Apply a DIY Undercoating or Rust Proofing Spray

There are many kinds of automotive undercoatings on the market, so do your research, read reviews, and when in doubt ask a reputable body repair shop for advice. Photo Credit: NH Oil Undercoating
There are many kinds of automotive undercoatings on the market, so do your research, read reviews, and when in doubt ask a reputable body repair shop for advice.
Photo Credit: NH Oil Undercoating

So by this point, you might be thinking, “Well shit, I can save some dough, and do this myself!”

Awesome idea amigo. But before you begin, there are several DIY tips and products you should probably procure prior to applying a rustproofing or prevention spray on the undercarriage of your car.

Undercoating applications can get really messy, really quick, and if you screw up the undercoating procedure, your vehicle could be out of service for a few days. Also, being that this procedure is both labor and time intensive, you will need to factor the whole “time is money” side of things into the equation as well.

But if you crunch the numbers, and it all adds up, then the following items should be procured prior to undercoating your car.

Materials Needed to Undercoat a Car

  • Degreaser products
  • A disc grinder and replacement pads in varying levels of abrasion
  • Power tool with wire brush
  • Air hose
  • Eye, nose, and hand protection
  • Sandpaper (200, 300, and 400 grit)
  • Sharp metal scraper
  • Undercoating and any required application tools/products
  • Car lift

The Undercoating Process

1. Clean

Surface corrosion will eventually turn into rust, and the longer it is allowed to fester, the harder it will be to remove.

Prior to applying a rust-repelling undercoating, you will need to remove as much corrosion build-up, caked-on road grime, and any other form of “crap-tastic” contaminant from the underside of the vehicle.

Here are a few of the core steps to completing this process.

Blast- Spray the entire underside of the vehicle with either a pressure washer, or a garden hose that has been outfitted with a heavy-duty spray nozzle. Be thorough, and hit every crevice and corner you can find, especially on higher mileage vehicles. Chances are you will be amazed by how much road gunk you will dislodge.

Degrease – Rinse complete, and undercarriage allowed to dry, it’s time to use a commercial-grade degreaser to remove any grime or oil lurking beneath the vehicle. The spray and walk away stuff allows you enough time to go get another beer, before removing the degreaser with shop rags or a blast of water.

Grind – The next step is to grind any large chunks of rust or hardened contaminants, starting with a mild grinding pad, and gradually moving to more abrasive pads as necessary. You can also use a stiff wire brush attachment on a power tool or a paint scraper, just beware of any electronics or hydraulic lines that could be damaged by these tools.

Sand – Corroded crap and contaminants blasted and scraped away, break out the sandpaper and get to hand scrubbing that underbelly. Start with a 200 grit sheet, and after each pass move a milder grit of sandpaper. This will not only remove any stubborn rust patches, but it will smooth out the scratches left behind by the coarser forms of scouring media.

IPA Time- No, we’re not talking about beer, even though suds and scrubbing do tend to go hand-in-hand on a hot summer day. We’re talking about using an isopropyl alcohol (IPA) blend and dry rags to wipe-down what will be getting undercoated. This final prep process helps ensure that the entire undercarriage is devoid of dust and other gunk.

2. Prime Time!

You should use a primer when applying  DIY undercoat which serves as the basecoat
Spraying a primer is a crucial step in the undercoating process.

Most DIY undercoating products require a primer of some sort to serve as a basecoat. We’ve found that the best primers are those with high zinc levels, as this provides an additional corrosion resistance. Just be sure to follow the manufacturer’s instructions, for many primers have their own unique prep requirements and curing times.

3. Undercoat

The final step is to apply the undercoating which will provide protection against contaminants that cause corrosion
Many undercarriage sprays are similar to spray-on bed liners.

The final step in the undercoating process is the application of the undercoating itself. Most of these products involve a two-stage or dual-layer spray-on procedure.

While the first round of undercoating should be relatively thin, know that it is not there to be the first line of defense, but to serve as a basecoat for the thicker outer coating. An hour or two of downtime on a warm day should provide ample cure time for this first layer. Once it becomes tacky to the touch, it’s time to move on to the final outer coating.

These final layers should be applied liberally, and in smooth, slow movements. Rushing will only cause uneven coverage and drips to form, so take your time. Once fully coated, it’s time to sit back and let your undercoating cure, which depending upon temps and the product used, may take anywhere from a few hours to a few days.

Can You Protect Other Car Parts From Corrosion?

Ceramic Coating - How It Works

If you’re looking for a long-lasting solution for preventing body panel rust and surface corrosion, opting for a nano ceramic coating is the way to go. 9H-rated ceramic coatings in particular are quite good at repelling rust.

Utilizing a highly-concentrated liquid polymer that’s been enhanced with liquid quartz, a.k.a. silica dioxide (SiO2), nano ceramic coatings seep into clear coats, chrome, bare metal, and other porous hard surfaces.

Once cured, nano ceramic coatings create a completely transparent, ultra smooth crystallized surface. This layer of protection repels everything from UV rays and acid rain, to bird droppings, tree sap, surface scratches, and the damage caused by most road chemicals.

Higher end ceramic coating for cars, like Armor Shield IX, also have the ability to reject electrolytes, therefore preventing them from penetrating surface areas, and thus, reducing the potential risk of corrosion.

Parting Shots

This poor chap had a complete car last week, but he decided to hold-off on undercoating his automobile, and now look at it. Photo Credit: Micah Wright
This poor chap had a complete car last week, but he decided to hold-off on undercoating his automobile, and now look at it.
Photo Credit: Micah Wright

Having an automobile treated with an undercoating is not only a smart way to extend the lifespan of the vehicle, but it also protects crucial brake and suspension components from seizing due to corrosion.

When properly installed, an automotive undercoating also has the power to keep an undercarriage shielded from all sorts of unsavory shit. This means everything for saltwater, deicers, road grime, engine oil, corrosive chemicals, and many other kinds of corrosion-causing contaminants get kicked to the curb.

However, it is still imperative that that you routinely wash your automobile (and its underside) with a pH balanced shampoo. Embedded contaminants will always do their damndest to wreck your ride, so break out that “winter coat” and don’t forget about the shiny topside, because it too is prone to rust and corrosion.

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