Do All Cars Rust Underneath?- Explained

The last thing you want to experience in your dream car is rust. But spotting signs of rust on your car is not always easy, especially if they are tucked away under the body. The effect and damages of rust on cars is always a nightmare for car owners but do all cars rust underneath?

Yes, all cars do rust underneath. However, today’s new cars come with underbody corrosion protection which safeguards the car’s base against rust. Unfortunately, the protection does not last forever. It means that even though it may take several years for many modern cars to show signs of rust, they will eventually rust underneath.

Many cars rust underneath. Some are more prone to rust than others, and the best way to protect your car from rust is to take the right measures as soon as you see any early signs of discoloration.

There are ways to prevent rust, such as using rust proof paint, which helps prevent water from seeping into the body, but it doesn’t always stop moisture and salt from finding their way through the seams, joints, and small nooks where parts are attached.

However, newer rust proofing materials can block air and moisture from contacting metal parts. Your local mechanic should be able to choose the right material to coat your vehicle with current products.

How Cars Are Protected From Rust Underneath?

The underside of your car is permanently exposed to environmental influences. In winter, rain, snow, and road salt are the main factors that affect the underside of the car. Road salt leads to the formation of rust and it poses a risk to the good condition of your car’s underbody.

How Cars Are Protected from Rust underneath

In summer, it is the heat, small stones, and sand that poses a risk to your car’s underbody. The dirt attacks and damages the vehicle’s body and chassis parts.

Modern cars have a full protective layer underneath from the factory. The underbody protection preserves the car by sealing its underside to protect it against environmental and climatic influences. In addition, the underside protection repels water and therefore protects against rain, snow, and road salt.

The protection absorbs gravel and pebbles well to prevent scratch or chipping. However, the underbody rust protection dries out over time. Therefore, you need to thoroughly check the protective layer underneath your vehicle at some point. If it cracks or flakes, then you need to act immediately.

How Long Can the Underbody Protection Prevent Rust?

As stated earlier, new cars have effective underside protection, but it doesn’t last forever. The external factors such as stones, sand, snow etc wear it down and the material is subject to ageing processes.

How Long Can the Underbody Protection Prevent Rust

For this reason, the underbody sealant should be renewed every six to eight years at the latest. This cycle is also recommended for the underbody protection of used cars, regardless of the material used.

What Material Is the Underbody Made of?

For a long time, bitumen-based underbody protection was widely used and applied to new cars and in the DIY sector. However, recently, wax-based protective products have been developed.

What Material Is the Underbody Made of

The skid plates of new cars now consist of a viscous PVC-based paste, a mixture of polymer powder, plasticizer, additives, and fillers. This protector hardens through additional heating.

If you use a bitumen-based sealant, you need to keep an eye on it. This material is subject to ageing processes, hardens, becomes brittle, cracks, and peels off. If this happens, the protective layer will no longer be effective. In the worst case, the dissolved road salt will now penetrate between the protective layer and the floor panel, where it can no longer escape.

From this point, the so-called salt corrosion occurs, which destroys the floor panel. Due to this disadvantage of the material, products based on bitumen are used less than wax-based protective products.

You should also take a closer look at other exposed areas. These are the tips, edges, and wheel arches. Stones and water splashes from the wheels place a greater load on the underbody protection.

Underbody Rust Protection and Cavity Sealants: What’s the Difference?

Moisture also enters cavities in the vehicle body during regular driving. If this happens regularly or if moisture accumulates there, it causes rust to form on the body. To prevent rusting, waxes or greases are applied to the cavities to form a permanently impermeable surface.

Underbody Rust Protection and Cavity Sealants: What's the Difference

Unlike the underbody protection, chipping in the cavities should not be expected, so the material used here is less elastic, but has better creep ability. The fact that grease and waxes reach every bend and every seal in the cavities provides effective protection against corrosion.

Renewing and Repairing the Rust Protection under Your Car

After about six to eight years, you will most likely need to renew or repair the old rust protection. However, repairing the underbody protection by spraying it with bitumen doesn’t work.

Renewing and Repairing the Rust Protection under Your Car

To protect the underside of your car from rust, the old anti-corrosion coating has to be removed first. The bad news is that this is quite time-consuming or expensive.

However, there is also good news. Only the damaged points have to be fixed.

These are often the edges of the skirts or wheel arches. The sealing of the central area of ​​the vehicle, on the other hand, usually lasts for almost the entire life of a car.

Removing Old and Weak Underbody Corrosion Protection

There are three ways to remove the factory anti-rust protection from your car’s underbody:

Removing Old and Weak Underbody Corrosion Protection

1. Manual Removal with a Spatula and Brush

Manual removal with a spatula and brush is very time-consuming. This procedure is ideal for removing loose parts that are cracked. In this method, you’ll rotate the brush and lightly run sandpaper over the tough asphalt. Only manual work can be effective here. However, a heat gun can make the job considerably easier, especially in areas that are not easily accessible.

2. Burning

Some tough car mechanics rely on the practice of burning to remove the factory underbody corrosion protection. However, we strongly recommend that you refrain from using this method because it is very likely that you will set the car on fire and perhaps, your entire workshop.

3. Sandblasting


Sandblasting is finally the most popular way to remove underbody rust protection. Here two different approaches are fundamentally differentiated: the abrasive and the non-abrasive method.

Abrasive sandblasting

uses solid granules that are accelerated with pressurised air and thrown against the underside of the car. The best-known procedure is sandblasting. However, a variety of other mediums are also available today, such as baking soda, glass, plastic pearls, walnut shells, and many more.

The advantage of abrasive sandblasting is that it guarantees good results. It allows removing the old protective layer quickly and thoroughly. In addition, it is a fairly inexpensive method. A disadvantage of abrasive blasting is that if the pressure is too high or you have chosen the wrong blasting agent, further damage may appear on your car’s bottom plate.

Non-abrasive sandblasting

this method is an effective alternative. Instead of working with solid shot blasting agents, dry ice blasting is performed with frozen carbon dioxide pellets. In contact with the underbody protection, the pellets explode and destroy it.

In addition, no waste results from dry ice blasting of the old protective layer, and this method is harmless to the bottom plate. Alternatively, the high-pressure water jet can also be chosen as a non-abrasive method. The disadvantage is that they are quite expensive. This solution is worth it for cars with a high value, such as sports cars or vintage cars.


Although every car is different, yet, none is completely free from the reach of rust. As explained, newer models can resist corrosion (rust) better than older ones but are still susceptible to rust. The major thing that helps cars fight rust is underbody corrosion protection. Also, cavity corrosion protection is helpful to prevent rust for a long time.

Evan Cooper

Evan Cooper

Hi, I’m Evan Cooper, the founder and an editor of this site, Doesitrust. I’m a chemical engineer and working in a rust-eliminating paint manufacturing company. Besides this profession, I’m a researcher and blogger.

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