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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Every car enthusiast knows that rust if left unchecked can eat away the metal of a vehicle. That’s why we use an undercoating to protect the car’s body (and underbody) from moisture, salt, acid rain, and other corrosive substances. An undercoat also evens out a car’s surface for a topcoat application and gives the topcoat finish a cleaner appearance. Our review aims to show you some of the best undercoating sprays currently on the market that will help keep your vehicle in good shape. 

  • Best Overall
    Dynatron 544 Dyna-Pro
    Summary
    Summary
    One of the best-rubberized undercoatings that provide all-weather protection against chipping, dust, salt, corrosion, and natural wear. It’s a combination of a spray on and easy brush formulation to provide the best finish that matches the OEM paint.
    Pros
    Pros
    Highly resistant to rust and corrosion. Forms a fully paintable layer. Suitable for all vehicle types. Protects your vehicle from natural wear. Sprays on easy. Dries quickly.
    Cons
    Cons
    More expensive than other undercoats. Doesn’t have great adhesion when used on an old undercoat or a greased surface. Short shelf life once opened.
  • Best Value
    Penray 4424 Rubberized Undercoat
    Summary
    Summary
    A rubberized waterproof coating that protects the surface from extreme temperatures, dust, road salt, and fumes. It can be used on wheel wells and automotive underbodies.
    Pros
    Pros
    Cheaply priced. Help reduce road noise when applied on wheel wells. Shows no bleed-through when painted over. Can also be used for minor roof and gutter repairs.
    Cons
    Cons
    Needs many coats to get the job done. Doesn’t stick on greased surfaces. Takes too long to dry when sprayed on a car’s underbody.
  • Honorable Mention
    3M 03584 Professional Grade Rubberized Undercoating
    Summary
    Summary
    An asphalt-based and rubberized undercoating that resists rust, corrosion, and protects against moisture. The spray spreads smoothly without clumping or dripping.
    Pros
    Pros
    Comes in a pack of six. Has an aerosol dispenser for easy spray-on application. A no-run formula for clean application. Has sound-deadening properties to reduce road noise.
    Cons
    Cons
    Needs multiple applications for the undercarriage. Unpleasant smell when wet.

Benefits of Undercoating

  • Save money. It’s expensive to have your car undercoated by a professional since it can cost hundreds of dollars for one session. Moreover, you would also have to wait for a couple of days before the job is done. Instead of spending a fortune on an undercoating service, buy a quick-dry undercoat and do the job yourself.
  • Reduce road noise. A vehicle’s undercarriage gets noisier as time goes by due to rust and wear. Most undercoats are formulated to seal all the nooks and crannies on the undercarriage that typically lead to road noise. 
  • Add an extra layer of protection. An undercoat typically acts as an additional layer of protection from mold, moisture, dust, and rot. It also protects your vehicle from dents, scratches, and paint chips.

Types of Vehicle Undercoating

Rubberized 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

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 Undercoating

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. 

Top Brands

3M

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

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

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.
  • Above $50: 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.
An undercarriage damaged by rust.
gettyimages

Undercoating sprays prevent rust from damaging your undercarriage. 

Key Features

Volume

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.

Shelf Life

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.

Formulation

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.

Other Considerations

  • 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 2019

Best Undercoating Overall: Dynatron 544 Dyna-Pro

Dynatron 544 Dyna-Pro
Amazon

The Dynatron 544 Dyna-Pro is one of the best undercoats for rust-proofing a car’s underbody. It offers all-weather protection and can last through an entire winter season. The coat leaves a smooth feel, even on a rusted surface, and has a glossy look to it. The spray is powered by 3M, meaning that its molecules are tightly bonded with an electro-mechanism to form a strong barrier against rust and chipping.  

The product comes with an easy brush and sprays and forms a fast-drying coating. You will have an easy time painting on the coating with a standard refinish paint system, and it will match any desired OEM color. Moreover, it has great sealing, anti-abrasion, and anti-corrosion properties. It also deadens the noise from the undercarriage.

Its main drawback is that the undercoat doesn’t have great adhesion on greasy surfaces or an older undercoat. You would have to rub them off before you apply the spray, and that can be time-consuming. It also has a short shelf life once opened and is more expensive than other rubberized undercoats.

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Best Value Undercoating: Penray 4424 Rubberized Undercoat

Penray 4424 rubberized Undercoat
Amazon

The Penray 4424 is a budget-friendly undercoat that can be painted over with no bleed-through. It’s also a waterproof formulation that forms a protective layer against dust, road salt, corrosion, and extreme weather conditions. Penray comes in an easy-to-use aerosol can for easy application, with no drips or clumps. Its rubberized formula acts as an insulator to minimize road noise.

The spray is designed to seal, protect, and rustproof metal surfaces. The undercoat blends well with color paint finishes and even with a matte black finish. The spray can be used on all automotive applications such as the frame, wheel wells, and undercarriage. It also works on home foundations and for minor repairs on roofs and gutters.

Its disadvantage is that it takes too long to dry, especially when applied on a vehicle's underbody. You may have to wait for at least two days for the undercarriage to dry. Moreover, despite being a cheap product, you will need to apply multiple coats, and you may run out of the 16-ounce bottle before you get the job done. However, this spray is suitable for cars, trailers, trucks, and RVs.

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Best Undercoating Honorable Mention: 3M 03584 Professional Grade Rubberized Undercoating

3M 03584 Professional Grade Rubberized Undercoating
Amazon

The 3M 03584 makes our list as a rubberized spray that can effectively remove any traces of corrosion, abrasion, and dust from a vehicle’s undercarriage. It’s also an asphalt-based spray with a no-run formula for easy application, meaning you won’t have to clean drips from your garage floor as you apply the undercoat. In addition, like a rubberized spray, it will form a durable barrier against moisture, grime, and grit.

The spray provides insulation to a vehicle's cabin to reduce the noise coming from the undercarriage as it gets older. The coating also seals up small cracks and holes in an old undercarriage to even out the surface. You can also use the coating on wheel wells, trunk lids, quarter panels, under the hood, and the interior side of fenders.

Its downside is that this undercarriage spray has an unpleasant smell when wet. You’ll also need to apply multiple coats to get a proper seal on the undercarriage and other metal surfaces. It’s also a newer undercoat in the industry and unfamiliar to many people. Despite that, the spray is suitable for trucks, RVs, and vans.

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Tips

  • 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 it 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.

FAQs

Q: Do I have to remove the wheels when undercoating the underbody?

A: 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?

A: 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: After how long should I give my vehicle a new undercoat?

A: A fresh undercoat should be applied once a year, and more so before the beginning of 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.

Final Thoughts

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.

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