Here at AvalonKing, our blogs typically consist of material that’s engineered to appeal to a broader automotive audience. But not today ya’ll…

This one goes out to all you northerners and seaside landlubbers, because today we’re going to discuss protective automotive undercoating products, and revisit some of the unfortunate side-effects associated with road salt and deicers.

No one likes riding around in rust-riddled, corrosion-covered, pitting piles of poop. It’s no secret that road salt and deicers cause rust to form on automobiles, an affliction that is equal parts unbecomingly embarrassing and dangerous. This is not small problem either, as every year rust gobbles-up billions of dollars in automotive repairs in the United States alone.

Most of these issues can be traced directly to magnesium chloride (MgCl₂). This readily available, inexpensive, naturally occurring chemical does wonders for thawing-out frozen precipitation, but it’s also a real bastard when it comes into contact with exposed metal surfaces. This shit is one hell of a corrosive chemical compound too ya’ll, because when it encounters the right blend of moisture and oxygen, it can cause all kinds of cancerous lesions to form on your vehicle’s exposed underbelly.

But I digress. The question we need to address today, is whether or not these undercoating products are still necessary. Cars of yesteryear were constructed from hardened steel, iron, and other durable metals. At the time, this was what automakers had to work with, and for as strong as these materials may have been, metals like these are notorious for oxidizing and rusting.

Nowadays, modern automobiles are constructed from far lighter, rust-resistant materials, like aluminum, plastic, carbon fiber, and a slew of other lightweight components. This not only makes them far more fuel efficient and inexpensive to manufacture and fix, but less susceptible to corrosive contaminants as well.

So, where does this leave automotive undercoating, and what is it made from? How does it work? Are there any major pros or cons to this stuff? And perhaps most importantly, is it even necessary in the first place?

Let’s break down the good, the bad, and the rusty, because today’s undercoating solutions are a far cry from the tar our ancestors used to slap on the undersides of their wagons.

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, it’s quite possible that you are already familiar with the term “undercoating.” If not, here’s a quick synopsis…

All vehicles come with some form of undercoating straight from the factory, with it being the first line of defense between an automobile’s metallic underside and the elements. But these OEM coatings are not always the most durable product, and will wear-out over time, leaving oil pans, transfer cases, suspension arms, and pretty much every other metal part found underneath a vehicle vulnerable to corrosion and rust.

Most dealerships offer an additional undercoating as part of a “winter package” option, which typically consists of a “rubberized” protective layer being sprayed across the entire undercarriage of the automobile. Once applied and allowed to cure, this undercoating has the ability to repel rust and oxidation, rock chips, scratches, and road noise.

But just because you have the ability to purchase this add-on option or service, or tackle the task on your own, doesn’t mean that you are going to follow through and make it happen. This is precisely why automotive undercoatings have earned a reputation for being a bit of an unreliable, double-sided sword.

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 is 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 underbody of your automobile, chances are you’ve come across the terms “rustproofing” and “rust protection.” Despite sounding identical, there are some key differences between these two approaches to rust prevention, even if their intended purpose remains the same.


Rustproofing is a process that involves the application of rubberized sealants, lanolins, or any number of other rust-repelling coatings on corrosion-prone surfaces on the underside of a vehicle. Some of the common areas that get “rust-proofed” include the undersides of fenders, weld points and seams, fuel tanks, suspension arms, axles and rear differentials, and chassis cradles. Pretty much any surface underneath the vehicle that does not get hot is fair game with this stuff, and it is not uncommon to see off-road vehicles rocking this stuff on rocker panels for additional outer protection.

Rust Protection

There is another term that can be confusing to consumers, and that’s rust protection. Rust protection is a manufacturing process that infuses rust-inhibiting chemicals into the materials that make our automobiles. These rust inhibitors are not topical coatings, but more of an engrained countermeasure to the circulation of electrical current, a critical component in the development of rust. Most modern automobiles have some form of rust protection ingredient mixed into their genetic makeup, which when paired with resilient materials like aluminum, creates a far more rust resistant surface area.

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. While almost many manufacturers utilize the term “rubberized” to describe a spray-on protective product, the ingredients they utilize are not what one might expect. Two of the more commonplace peculiarities include calcium carbonate (the primary component in eggshells, snail shells, seashells, and pearls), and asphalt.

What are the Different Methods to Apply Undercoating?

Photo Credit: FLUID FILM/YouTube

If you’re considering investing in an undercoating, you’ll have to decide which direction you want to go in regard to its installation. While dealer-installed options are typically limited by manufacturer related red-tape, a privately held service repair shop will have its own options for you to choose from, and therefore provide more flexibility. Just make sure that the shop is certified and has favorable reviews, because the last thing anyone wants is shoddy workmanship and shitty customer service.

Regardless as to which direction you choose, the methods used during the undercoating application process tend to be the same across the board. So here is what you can expect from a pro install…

1. Spray-On “Rubberized” Undercoatings

Photo Credit: AMMO NYC/YouTube

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, acting as a barrier against salt, moisture, oxygen, and other foreign substances that may lead to rust and corrosion. We’ll get into the grimey details of what makes these opaque products so popular, and what to watch out for a little later on in this article.

2. Electronic Rust Inhibitors

Photo Credit: ERPS

Electronic rust inhibitors are marketed as a permanent, discreet, easy to install solution to corrosion. But the jury is still out as to whether or not they actually make a damn bit of difference when it comes to repelling and removing rust on automobiles. 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

Photo Credit: FLUID FILM/YouTube

When choosing an undercoating, the lanolin approach remains a proven, if not slightly strange 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.

When it’s sprayed, lanolin fills in all of the nooks and crannies of the chassis with a sticky, wax-like substance. Curing times will vary depending upon air temperature and how heavy of a coating has been applied, so there will likely be 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 has 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 unseen areas that are prone to rusting-out.

How Does Undercoating Protect from Rust?

Photo Credit: Micah Wright

A while back, we wrote an article about corrosion protection, and how ceramic coatings can help reduce the risk of rust build-up. In that article, we outlined the chemistry behind what causes rust, which is best summed-up by the following, oh-so super scientific statement.

“Rust formation is kind of like spending quality time with your cool uncle at the local strip club. For this electrochemical process to occur you will need a very generous anode handing out electrons (your drunk uncle), an electrolyte (the liquid that’s causing him to be so generous), and a cathode (a g-string that’s hungry for attention).”

Super professional synopsis out of the way, we turn toward how we can interfere with this corrosive molecular catastrophe. An undercoating is intended to block the contributing factors that lead to corrosion, and here is how each one is intended to work.

Coating 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…

Electric Shock Therapy

Utilizing an “electric shock” method, like the one we 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 is designed to be a permanent solution, and one that does not need reinstallation or routine servicing. The only issue is that it really doesn’t seem to work so well on automobiles as opposed to say, tug boats, and it’s also quite expensive.

The Pros and Cons of Applying an Automotive Undercoating

Photo Credit: NH Oil Undercoating/YouTube

Although the underside of the average new vehicle comes shielded straight from the factory, those of us living in cold-weather regions, or areas along the coastline, probably should consider having another undercoating applied. But what are the downsides, if any? And more importantly, do the positives outweigh these setbacks?

Undercoating Pros

The biggest advantages to having an undercoating installed on the underside of an automobile is the peace of mind that comes with knowing that your vehicle is protected from rust and corrosion, at least, to an extent. While there are no guarantees that a rust bubble won’t appear where a rock chip removed some rubberized 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 effective as a dedicated sound-proofing product, and won’t do much when it comes to repelling heat and cold, thickly sprayed undercoatings do reduce road noise, if but in minimal increments.

Undercoating Cons

Photo Credit: NH Oil Undercoating

1. Talk About Some Seriously Toxic Stuff!

You should always wear a ventilation mask, protective eyewear, gloves, and a painter’s suit when working with undercoatings. Like many chemical-rich products, the average undercoating is a gateway to organ failure, cancer, infertility, and genetic defects. A bit of digging revealed that quite a few brands are still unsure as to what this stuff actually does to the human body over time, with some of the more discerning case studies showing that “…25% of the mixture consists of ingredient(s) of unknown acute toxicity.”

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

D-a-a-a-a-a-d jokes aside, Lanolin has earned the nickname wool grease for a reason. This waxy substance is derived from a naturally occurring secretion commonly found in fluffy animals like sheep. Produced within the glands that encapsulate their wool follicles, lanolin provides these cud-chewing critters with a waterproof coat that helps keep them dry and warm in winter. This makes breeds like the ultra-fluffy Merino breed of sheep quite the hot commodity, and by hot, we’re not talking about those underpants your grannie just knitted you for your birthday.

On the downside, because lanolin is basically the porous substance secreted by livestock, it smells sort of like… well… stank-ass sheep glands. This repulsive aroma is even more notable when lanolin is exposed to warmer temperatures. So if you notice that no one is parking next to you in summer, it might be because they can’t stand the strange stench of your vehicle’s 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 underneath seems like a brilliant idea… right? Wrong.

“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 issue people have with professionally installed automotive undercoatings and rustproofing procedures, is how much they cost. Sure, the initial shock of having to cough-up a few hundred bucks so that a professional can undercoat your vehicle may be shocking, it is nothing compared to the cost of replacing an entire vehicle due to rust damage. 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, a topic that we will visit here shortly.

How long does an undercoating last?

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.

How to Apply a DIY Undercoating or Rust Proofing Spray

How to remove rust and undercoat your truck for under $40!

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 friend, there are several DIY tips and products you should probably procure or consider prior to applying a rustproofing or prevention spray on the undercarriage of your car. This stuff can get really messy, really quick. Your vehicle could also be out of service for a few days if you screw up the undercoating procedure, and being that this procedure is always both labor and time intensive, you will need to factor the whole “time is money” side of things as well.

But if you crunch the numbers, and it all adds up, making you all the more hell-bent on conducting a rust-proof undercoating install on your own, here is a rough synopsis of what you should keep in mind and have on hand.

Materials Needed

  • 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

Prior to applying a rust-repelling vehicle undercoating, you will need to remove all excessive corrosion build-up, caked-on road debris, or any other crap-tastic contaminant from the underside of the vehicle.

Here’s a quick rundown on the steps involved in the automotive underbody cleaning 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 stage complete, and undercarriage relatively dry, it’s time to use a high-quality, commercial-grade degreaser to remove any grime or oil lurking beneath the vehicle. While different products have their own instructions, we recommend the spray and walk away stuff. This allows us enough time to crack open another beer, before coming back to remove the degreaser with shop rags or a blast of water.

Grind – The next step is to grind any large chunks of rust or hard contaminants from areas you wish to coat. It’s a good idea to start with a mild grinding pad and take a progressive approach, moving to more abrasive pads only when deemed absolutely necessary. You can also use a stiff wire brush attachment on the end of a power tool instead, just remain aware of any electronics or hydraulic lines that could be damaged by these extremely abrasive scouring tools.

Sand – Corroded crap and contaminants removed, break out the sandpaper and get to hand scrubbing that shit. Start with a 200 grit sheet, and slowly work your way toward a 400 grit sheet, as this will not only remove stubborn rust patches, but the scratches left behind by your coarser scouring media.

Have Some IPA- 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 all of the undercarriage that will be getting sprayed. 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

Most of the undercoating products for DIY consumers require a primer of some sort to serve as a basecoat. We’ve found that the best type of primers are those with high zinc levels, as this provides an additional layer of corrosion resistance if the undercoating surface layer is penetrated or compromised in some way. Just be sure to follow the manufacturer’s instructions, for different primers have their own requirements for achieving optimal results.

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 bed liners

The final step 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 the basecoat for the far thicker outer coating. An hour or two of downtime on a warm day should allow this first layer ample time to cure, and once it becomes tacky to the touch, it’s time to move on to the final outer coating.

These secondary layers should be applied liberally, and in smooth, slow movements. Rushing will only cause overcoating headaches and uneven coverage, so take your time, and when in doubt, refer to the manufacturer’s instructions. Once fully coated, it is time to let your undercoating cure, which depending upon temps and product used, may take anywhere from a few hours to a few days.

Can Your 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 ceramic coating is the way to go. A 9H-rated ceramic coating utilizes a highly-concentrated liquid polymer that is primarily formulated from liquid quartz, a.k.a. silica dioxide (SiO2). When this liquid coating is applied, it seeps into the clear coat and other porous surfaces, thus creating an ultra smooth crystallized surface.

Once cured, high-end ceramic coatings create a semi-permanent, completely transparent, super strong outer shell. This layer of protection not only blocks UV rays, but resists scratches, the effects of acid rain, and damage caused by most road chemicals. Higher end ceramic coatings, like Armor Shield IX, also have the ability to repel electrolytes, therefore preventing them from penetrating surface areas, and thus, reducing the potential risk of corrosion.

Parting Shots

Photo Credit: Micah Wright

When properly installed, a high quality undercoating has the potential to keep the undercarriage of an automobile shielded from all sorts of unsavory shit. Saltwater, deicers, road grime, oil, chemicals, and pretty much any other contaminant that can cause corrosion and rust to form are either repelled or remains stuck on the outer layer’s surface. This is why it is imperative that even with an undercoating in place, that you regularly wash the underside of your automobile, as embedded contaminants will do their damndest to slowly eat through an undercoat.

That said, rust protection is very much a logical option for those living in colder climates, or within coastal communities. Having an automobile treated with an undercoating is not only a smart way to extend the lifespan of a vehicle, but protect crucial brake and suspension components from seizing-up due to corrosion.

So break out that “winter coat” and don’t forget about the shiny topside of your vehicle, because it too is prone to rust and corrosion. If you require a little insight into the matter, feel free to peruse our in-depth look at the horrifying effects of road salt and deicers on automobiles. Chances are you will be mortified by what we discovered…

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