Best Undercoating: Keep Rust from Eating Away Your Car

Our top picks for the best undercoats with the best rust preventive formula.

byNoelle Talmon| UPDATED Oct 18, 2022 12:14 PM
Best Undercoating: Keep Rust from Eating Away Your Car

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BYNoelle Talmon/ LAST UPDATED ON October 18, 2022

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.

Best Overall
Dynatron 544 Dyna-Pro

Dynatron 544 Dyna-Pro

Summary
One of the best rubberized undercoatings that provides 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
  • 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
  • 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
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
  • Cheaply priced.
  • Helps 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
  • 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.
Most Versatile

3M 03584

Summary
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.
Pros
  • The coating seals up small cracks and holes
  • You can also use the coating on wheel wells, trunk lids, quarter panels, under the hood, and the interior side of the fenders
Cons
  • Unpleasant smell when wet.
  • Need to apply multiple coats.
  • Newer undercoat in the industry and unfamiliar to many people.

Summary List

Why Trust Us

Our reviews are driven by a combination of hands-on testing, expert input, “wisdom of the crowd” assessments from actual buyers, and our own expertise. We always aim to offer genuine, accurate guides to help you find the best picks.

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Our Methodology

We can’t put our own hands on every item available. In these instances, we put our collective experience in journalism, research, and prior product testing to use to make our product picks. Items that are used by our own staff may get earnest endorsements as well, but we’ll never accept fees or bonuses to sell you stuff we’re not actually excited about. Affiliate revenue is always disclosed.

The Drive aggregates reviews and research from all over the internet to figure out which products are worth buying. We also put out shopping guides to help you understand how to assess the value of these things on your own. As our editorial cousins at Car Bibles say, “Knowledge is horsepower!”

Best Undercoating Reviews & Recommendations

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.

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.

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 the 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.

This non-toxic, rust-preventive lubricant is a durable and thixotropic liquid that's used in the aerospace, aircraft, and automobile segments. It's solvent-free, won't dry out, and will penetrate to all metal bases. It provides corrosion protection and salvages significantly corroded and frozen parts, including nuts and bolts.


Overall, this is an excellent rust preventive coating for cars and trucks. It creeps into all the corners and crevices on your vehicle's underbody for optimal coverage. It is also easy to apply, is all-natural, and repels water, snow, and ice while retarding rust.


However, the product is gooey and has a strong odor. During the first few drives, it may produce some white smoke.

This rubberized undercoating spray is designed for bare or primed metal underbodies on automobiles, trucks, trailers, and RVs. It protects against corrosion as well as water, salt, and chemical damage. Each 15-ounce can covers 10 to 15 square feet and dries to the touch in 60 minutes. The product has a wide spray tip with any-angle technology, so you can easily paint your vehicle while the can is upside down.


This undercoating lays down nicely and produces a smooth low-luster finish if you do several light coats. It covers most surface rust without any issues and dries pretty evenly, even if you overspray in some spots. It's also really easy to use and some really like the reptilian-textured surface it creates.


One downside is this product doesn't appear to be much different from the non-professional version. Also, the coverage isn't particularly thick, and it may splatter a bit when you spray it.

POR-15's rust preventative coating permanently stops rust and can be applied on sandblasted, prepped rusted, and seasoned metal surfaces. The formula creates a hard, non-porous finish that doesn't crack, chip, or peel. It protects metal from corrosive contaminants as well as salt and moisture. POR-15 is also resistant to acids and alkalis and repels fuels and oils.


This undercoating covers the vehicle really well and dresses up the metal. Its rust-proofing capability is top notch, and once it sets, nothing can get through it. It’s worth the time and money and provides some peace of mind because you only have to paint the surface once and never worry about rust again.


However, the product is sensitive to UV light and must have a top coat if the surface area is exposed to sunlight. It is also very messy and stains anything it comes into contact with, so you have to be careful when you are using it.

The Barrier Bond - No Drip Rust-Proofing Coating is a solvent-free rust inhibitor and undercarriage protectant. You can use it on both ferrous and non-ferrous metals. The formula is designed to match OEM equipment and prevent damage caused by corrosion, rust, salt, rock, and gravel.


This is a non-drying formula, so it flows into small, hard-to-reach spaces. It penetrates the base of the metals, provides long-lasting protection, and holds up in various types of weather conditions. The product displaces water and leaves behind a thin translucent coating that won't gum up in the heat. Simply remove dirt, loose rust, and other debris before applying Barrier Bond to the surface, and let it sit for six hours before exposing your vehicle to wet roads.


One downside is that it's a little pricey compared to some other products. Also, it's a non-drying formula, which may not be what you're looking for.

The Woolwax vehicle undercoating is excellent for automotive use as well as battery terminals, heavy machinery, boat trailers, lawnmowers, garage door tracks, and more. The lanolin-based, nontoxic formula works well in automotive and marine environments to prevent corrosion, provide lubrication, and displace water. It's long-lasting, won't dry out, and penetrates to the base of all metals.


The odor-free formula can be applied using an undercoating gun with 70-90 PSI. It is non-conductive, so it won't harm electrical connections. It's easy to stir and pour from the can, flows well, and holds up over time. Overall, it does what it says it will do and is versatile in its application.


However, the product is a little pricey. Some users also compare it to Fluid Film, but it's not quite as thick.

The Krylon Automotive Undercoating is one of the least expensive options on our list, so you really can't go wrong if you try this product. Its paintable and flexible formula is designed to protect your vehicle's underside as well as corrosion resistance. It's designed for interior and exterior use and can be applied on metal, wood, and fiberglass.


One can covers 16 square feet, and it dries in 24 hours. You can safely use it on your vehicle's wheel wells, gas tank, frame/supports, weld joints, floor pans, doors, and quarter panels. The matte black finish provides good coverage, adheres well to properly prepared surfaces, and it's easy to use overall.


However, if you get more than one can from different batches, the color may be a little inconsistent. Also, you need to use the entire can at once, or it won't work well.

Our Verdict

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.

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.

Best Undercoating Pricing

You'll spend between $20 and $50, but that doesn't include labor, time, or application methods. So you'll likely end up spending about $100 to $150 total.

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 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.

FAQs

You've got questions. The Drive has answers.

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.

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