Avoid These 7 Spots When Applying Undercoating

Many vehicle owners spray undercoating to prevent and stop rust, especially during winter and for people who stay in rust-prone zones.

While undercoating works, either way, you can’t just take a can and spray it all over the undercarriage.

There are some areas on your vehicle that you shouldn’t spray undercoating.

Quick Answer

As a whole, you should not spray undercoating on brakes, exhaust pipe, exhaust engine, drive shaft, tires, sensors and cameras, and suspension components, as this can result in unpleasant situations. 

While spraying all over the undercarriage may seem harmless, you may one day inhale fumes from the undercoat without knowing the cause.

Therefore, you should know where not to spray undercoating to prevent future dangers like that. 

Read through to learn more about the no-spray zones on the undercarriage.

Where Should You Not Spray Undercoating?

Applying an undercoat requires caution. You might be eager to inhibit or prevent rust from the undercoat.

However, you must ensure the undercoating doesn’t get to some areas to avoid disaster.

First, you must read the instructions on the product and consult with the manufacturer for the best application process. 

Quick Answer

As a general rule, here are the places you should not spray undercoating: 

  • Brakes
  • Rubber
  • Exhaust engine
  • Tires
  • Suspension components
  • Driveshaft
  • Sensors and cameras

Waxed-based, lanolin-based, asphalt-based, and rubberized undercoats have similar application processes and functions.

However, you should know that undercoats aren’t safe on all undercarriage surfaces; hence, you should read the manufacturer’s instructions.

However, for the time being, here are places to keep away from undercoating and why: 


You shouldn’t spray undercoating on the brakes.

It’s okay to spray the drum brakes and backing plates; however, you must be careful to prevent the undercoating from going beyond. 

Ensure you cover the calipers and disc brakes to prevent the undercoating from contaminating them.

While undercoating may not compromise brake safety, you may notice new noises when you brake your vehicle.


Some non-oil rubber doesn’t react well to undercoating products and may swell when you spray the undercoat on them.

If you have those rubber types on your engine mounts, suspension bushing, body mounts, CV boots, or anywhere else on the undercarriage, you should keep undercoating away from them.

Mask off those surfaces during the application; otherwise, they may swell.

Exhaust Engine

You shouldn’t spray undercoating on anything that gets hot on the undercarriage, like the exhaust engine or pipe.

Otherwise, they will fume whenever they’re hot. 

When this happens, you’re likely to inhale those unhealthy fumes as you drive your vehicle.

In addition, the fumes smell bad, and it may take a while to get the smell out.


Rubbers don’t rust, so there’s no need to spray undercoating on the tires.

However, mistakes are possible, and you can get some undercoatings on the rubber while you work. 

This can result in slippery tires or make a mess that requires additional stress and time to remove.

Therefore, you should remove the wheels before starting an undercoating process to prevent that.

Suspension Components

Overall, you can spray oil-based and waxed-based undercoating on the suspension components without negative effects.

However, other thick undercoating products may prevent them from functioning properly.

Therefore, you should consult the manufacturer’s instructions about the product before using it.


Some undercoatings are safe for the drive shaft and have no repercussions.

However, if the products are applied as a thick, gooey paste, you should keep them away from your drive shaft.

Otherwise, your car may end up with a vibration.

Sensors And Cameras

Some recent truck models now have advanced driver assistance systems, which means the sensors and cameras may be mounted around the undercarriage.

If your vehicle has this set-up, you should be careful when spraying undercoating to avoid getting the product over the surface. 


Undercoatings are safe to an extent; however, they’re not fit for use on every surface.

You shouldn’t spray them over the drive shaft, exhaust engine, rubber, tires, and other surfaces suggested in this article. 

Mostly, thick and gooey undercoating products seem unfit for all undercarriage surfaces, so you should use them with caution.

Overall, always consult the manufacturer’s instructions before spraying the undercoating to prevent issues with your car.

Key Takeaways:

  • Spraying undercoating on the exhaust engine and pipes can cause foul smelly fumes when hot.
  • Spraying undercoating on the drive shaft can result in vibration.
  • Use thick, gooey undercoating products with caution.
  • Always read the manufacturer’s instructions before using any undercoating product.