Best Undercoating: Keep Rust from Eating Away Your Car
Our top picks for the best undercoats with the best rust preventive formula.
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BY Noelle Talmon / LAST UPDATED ON July 6, 2021
Best OverallDynatron 544 Dyna-ProCheck Latest Price
Best ValuePenray 4424 Rubberized UndercoatCheck Latest Price
Most Versatile3M 03584 Professional Grade Rubberized UndercoatingCheck Latest Price
Most DurableFluid Film Rust & Corrosion ProtectionCheck Latest Price
Honorable MentionRust-Oleum Professional Grade Rubberized Undercoating SprayCheck Latest Price
Rust is the enemy for car owners because it can destroy the metal. Over time, pieces of your vehicle will start falling apart. That’s why it’s essential to keep rust in check. One way to do so is by applying an undercoating to the underbody of your car or truck. Undercoatings are designed to protect the bottom of your vehicle from salt, rock, gravel, moisture, and other corrosive substances. You can use these products to even out the surface area or as rust converters. There are many types of undercoatings available online and in stores, so it can be tough to choose the right one for your needs. We feature some of the best options in the buying guide below.
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Benefits of Undercoating
- Save time and money. If you pay a professional to put an undercoating on your vehicle, it can be costly. Plus, you have to make an appointment, set time aside to bring your car to the shop and wait for the results. If you do the job yourself, you'll save a lot of money, and you can choose when and where you want to do the project.
- Minimize road noise. Over time, your vehicle's undercarriage can rattle a bit due to age and rust-related calamities. Undercoat products are designed to fill in the small spaces and seams beneath your vehicle that can be noisy when you're driving.
- Provide additional protection. The best undercoat formulas will provide an extra layer of protection against dust, moisture, and corrosion. You have to worry less about gravel and other elements that may harm the undercarriage.
Types of Vehicle Undercoating
Rubberized undercoating is easy to apply, and generally offers the best protective coating for your car’s undercarriage. It cushions surfaces against moisture, rust, dings, and dents. Rubberized undercoating is safe to use on quarter panels and wheel wells and dries with a soft rubbery finish.
Asphalt-based undercoating offers a higher level of protection suitable for large trucks, recreational vehicles, and heavy machinery. It’s formulated with some bits of rubberized material to aid in noise reduction. It offers extra protection against chips and moisture but is not paintable and, therefore, only suitable for undercarriages.
Polyurethane coating is easy to apply and works by sealing up cracks and seams. The compound displaces salt and moisture and protects the unoxidized metal from rust. It’s often sold in canisters that are ready to preload into an application gun. It, however, requires some surface prep work before application, like degreasing, and applying an etching primer to the bare metal.
Wax or Paraffin-Based Undercoating
Wax or paraffin-based undercoating sprays are the cheapest and quickest options available. However, their results don’t last long, and you may have to apply a fresh coat after only a few months. In addition, the wax isn’t very adhesive on a metal surface. Its main advantage is that it seeps quickly into cracks and seams, and offers moderate protective properties against moisture.
3M is a multinational mining and manufacturing company that produces consumer products for the healthcare industry, energy industry, and automotive world. The company was founded in 1902 and is headquartered in Minnesota. Some of its top products are the Dynatron 544 Dyna-Pro and the 3M 03584 Professional Grade Rubberized Undercoat.
Penray is a global manufacturer of chemical products for marine equipment and the automotive industry. The company has been in existence for over 60 years, and its products are engineered to keep your vehicle operating at its optimal performance level. One of its best-selling products is the Penray 4424 Rubberized Undercoat.
Rust-Oleum is an Illinois-based manufacturer of protective coatings and paints for home and industrial use. Robert Fergusson founded the company in 1921, with the aim of manufacturing products that reduced corrosion on metal decks. The company has a number of brands under its umbrella, including NeverWet, NanoShield, American Accents, and Seal Krete, among others. The Rust-Oleum Rubberized Undercoating is one of its top-rated car undercoating products.
Best Undercoating Pricing
- Under $30: At this price range, you will find a number of high-quality products that offer the best protection to the underside of your vehicle. For undercoating agents, a cheaper product doesn’t mean that it’s low quality. It may be cheap due to its packaging or volume.
- $30 to $50: This mid-range price level is for undercoats that come with an underbody spray applicator and may be sold in packs of four or less. Most products here are packaged in bottles of 11 to 32 ounces.
- $50 and up: This higher price range is for top brand undercoats that are formulated to provide all-weather protection for your vehicle and offer maximum protection against rust. Most products here are packaged in 1-gallon bottles.
Vehicle undercoating products come in volumes from 16 ounces to about 5 gallons. Think of how much undercoat you will use in the current job, the size of your vehicle, and how much you will need to buy in the near future. A 16-ounce bottle is suitable for a small car, but an RV or a truck will need a 1-gallon jug to get the job done.
Most premium undercoating materials have a shelf life of at least one year after being opened. Others can only last for a few months, then they start to wear off. If you find a fully functional product with a short shelf life, it’s prudent to buy it in small portions. Figuring that you will use the undercoat at least once a year, the shelf life shouldn’t be an issue if you go for the right portions.
The formulation you choose depends on your budget and how long you want the coat to last. Rubberized and asphalt-based undercoats are more expensive, but a single coating job can last up to a year or longer depending on the environmental conditions. Cheaper options like paraffin-based formulations last for only a few months, and you may not be able to stand the smell.
- Functionality. The undercoating spray should be able to at least prevent rust and corrosion on the metal surface. It should also be paintable, have sound deadening properties, have quick drying time, and improve the aesthetics of the sprayed surface.
- Filling Power. The filling power is a measure of the undercoat’s ability to seep through cracks and holes, to smoothen out irregular surfaces. An even surface sets a great base for the topcoat paint and makes the vehicle's body look more appealing.
Best Undercoating Reviews & Recommendations 2021
- Use a pressurized washer to clean dust, dirt, mud, and road debris from the underbody before you apply the undercoat. You will have an easier time applying the undercoat when the surface is clean.
- Before undercoating, do a test spray to see the fan pattern of the bottle. If the coating comes out in a narrow stream, spray the coating up and down to get a proper coat. If it’s a tall fan spray, we suggest that you spray it from side to side.
- Use a degreaser to remove grease from metal surfaces before applying the undercoat. Most coats do not stick on greased surfaces, no matter how long you leave them to dry.
- Wear a mask and safety goggles when washing and undercoating your vehicle. That way, you protect yourself from inhaling or coming into contact with the cleaning chemicals and undercoating agent, which could potentially have serious health effects.
Q: Which rust proofing is best?
There are several ways to protect your vehicle from rust, including using a drip or dripless oil spray, an undercoating, or an electronic rust protection system. We include many good options in this buying guide.
Q: Does undercoating really work?
Yes. It provides a protective barrier that keeps out moisture, salt, and other substances that can potentially harm the underside of your vehicle.
Q: Is Fluid Film the best undercoating?
Fluid Film is a very effective undercoating used in the automotive and aerospace industries, and its reputation precedes it. However, several other products also do an excellent job of protecting your vehicle’s undercarriage.
Q: Do I have to remove the wheels when undercoating the underbody?
Yes, you do. For starters, you will get a chance to clean the wheels as you clean the underbody. Additionally, you will have enough room to spray the undercoat under the wheel wells and have better access to the underbody.
Q: What should I use to clean my vehicle before applying an undercoat?
You need a pressure washer or an air hose to get rid of dirt from the crooks of the underbody. In addition, you need a rim cleaner, engine cleaner, degreaser, and cleaning chemicals to get rid of rust and other tough stains on metal surfaces.
Q: How often should I give my vehicle a new undercoat?
A fresh undercoat should be applied once a year, and more so before the beginning of the winter season, as your tires tend to flick up moisture, ice, rocks, and dirt at your vehicle's body. If you live near the sea, particles of salt tend to take off some undercoat. In that case, apply a new coat at least twice a year.
The Dynatron 544 Dyna-Pro undercoat is our top pick as it provides all-weather protection, spreads easily, and dries quickly.
If you are looking for a budget-friendly undercoat that will keep your undercarriage from being eaten away by rust, try the Penray 4424 rubberized Undercoat.