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How do you use rust barrier?

Rust is a major problem that affects vehicles worldwide. As vehicles age, they develop rust on the body and frame which can lead to expensive repairs or make the vehicle unsafe to drive. Using a rust barrier is an effective way to prevent and protect against rust formation. In this comprehensive guide, we will examine what rust is, the benefits of using a rust barrier, and provide instructions on how to properly apply rust barrier for maximum protection.

What Causes Rust on Vehicles?

Rust is caused by a process called oxidation, which occurs when iron or steel reacts with moisture and oxygen. As iron oxidizes, it develops the familiar red-brown flaky coating we know as rust. On vehicles, rust commonly forms in areas that are exposed to the elements like the undercarriage, wheel wells, and lower body panels. Road salt, dirt, debris, and moisture promote rust formation and speed up the oxidation process. Vehicles in coastal climates are also vulnerable to rust from the salt air. Rust spreads quickly as it eats away at the metal beneath it, leading to corrosion and causing the metal to weaken and deteriorate over time.

Benefits of Using a Rust Barrier

Applying a rust barrier offers many benefits for your vehicle:

  • Prevents new rust from forming by blocking moisture and oxygen from reaching metal surfaces
  • Stops existing rust and corrosion from spreading further
  • Protects body panels, the frame, undercarriage, and other components
  • Reduces the need for rust repair down the road
  • Helps maintain the structural integrity of the vehicle
  • Extends the life of a vehicle prone to rust issues

Rust barriers work by adhering to metal and creating a protective coating that waterproofs and seals out moisture. Many formulas also contain rust inhibitors that prevent oxidation. Professional-grade rust barrier sprays and coatings provide long-lasting protection against rust for many years when properly applied.

Prep Work Before Applying Rust Barrier

Proper preparation is key to ensure the rust barrier bonds well and provides maximum protection. Here are some tips for prep work:

  • Wash the vehicle thoroughly to remove dirt, salt, and debris using a power washer if needed.
  • Inspect for existing rust and use a wire brush or sandpaper to remove any loose flakes or scales.
  • For heavy rust, use a rust converter product to neutralize and transform rust into an inert protective coating.
  • Sand and spot prime any areas with paint damage to provide a smooth surface.
  • Mask off any rubber, plastic, glass, lights, or trim to avoid overspray.
  • Perform small repairs like filling seams or holes as needed.

Proper preparation removes contaminants, lets you address existing rust, and creates an ideal surface profile for the barrier application.

How to Apply Rust Barrier

Here is a step-by-step guide for applying rust barrier spray:

  1. Position the vehicle on a lift if possible to access the undercarriage. Ramps or jacks can also be used to raise the vehicle.
  2. Shake the rust barrier spray can vigorously for 60 seconds before starting.
  3. Adjust the nozzle to provide a wide, even spray pattern.
  4. Hold the can 6-12 inches from the surface and apply a light first coat to all underbody surfaces needing protection.
  5. Allow the first coat to dry for at least 60 minutes.
  6. Apply a second heavier coat to build up the barrier. Focus on vulnerable areas prone to collect moisture like wheel wells, seams, and brackets.
  7. Allow the final coat to dry for 24 hours before driving the vehicle.
  8. For added protection, apply an additional coat or two over the next few weeks.

Tips for spray application:

  • Apply in dry, well-ventilated conditions above 50°F.
  • Use smooth back and forth passes, slightly overlapping each stroke.
  • Keep the can the same distance from the surface.
  • Coat inside body cavities and enclosed areas.
  • Mist hard to reach spots using the provided tube extension.
  • Go over uneven surfaces and seams to ensure complete coverage.

Key Areas to Coat

For comprehensive protection, focus on coating these vulnerable underbody areas:

  • Wheel wells and inside fender walls
  • Rockers and pinch weld seams
  • Frame rails and cross members
  • Body mounts and suspension components
  • Brake and fuel lines
  • Around gas tank and exhaust system
  • Doors, trunk, hood, and hatch seams
  • Battery tray and wiring harnesses
  • Inner fender aprons front and rear

Also spray inside enclosed sections like rocker panels, pillars, and sill plates. Thoroughly coating these areas provides a seamless moisture barrier.

How Long Does Rust Barrier Last?

When properly applied, rust barrier sprays can protect for 3-5 years or longer depending on the product and application process. Higher-quality rubberized coatings tend to last the longest.

Here are some factors that affect lifespan:

  • Quality and thickness of coating – More coats provide longer protection
  • Application prep work – Proper surface cleaning improves adhesion
  • Where vehicle is driven – Snowy and coastal climates reduce lifespan
  • Regular underbody washing – This removes corrosive dirt and salts
  • Touch up as needed – Spot reapply annually in trouble spots

Checking under the vehicle periodically and reapplying rust barrier in needed areas will provide ongoing protection against rust over many years.

Tips for an Effective Rust Barrier Application

Follow these tips for great results from your rust barrier application:

  • Remove undercoating or other coatings – Apply to bare metal for best adhesion
  • Address existing rust before applying barrier
  • Coat the entire underbody including enclosed areas
  • Apply 2-3 coats allowing proper drying time between coats
  • Use steady back and forth motions keeping the can a fixed distance away
  • Make sure to coat seams and joints thoroughly
  • Wear gloves and eye protection when applying
  • Perform annual touch ups to maintain protection

Common Questions

What kind of spray tip should I use?

Use a wide spray tip to cover large areas more efficiently. A medium spray tip can be used for more precise application in tight areas. Always test spray pattern on cardboard before applying to your vehicle.

Can I use rust barrier on the exterior paint?

Most rust barrier sprays should only be used on the underbody and not exterior paint, as they can cause drips, runs, and discoloration. Specialized rubberized undercoating designed for wheel wells and rocker panels may be safely used on some exterior painted metal when applied carefully.

How do I remove overspray?

Use a razor blade on glass and rubber trim to gently scrape off any overspray. On paint, use a clay bar lubricated with detailing spray to safely remove overspray without damaging the finish.

Can I apply rust barrier over existing undercoating?

It’s best to remove any old undercoating or rust encapsulator before applying a new product. Wire brushing, scraping, or grinding can be used remove existing coatings from metal for optimal adhesion.

What kind of maintenance is required after application?

Keep the underbody clean by regular washing, especially after winter driving. Check annually for any thinning areas or breaks in coverage and spot apply additional barrier as needed to maintain protection.


Rust barrier spray provides an easy and affordable way to protect your vehicle from the damaging effects of rust and corrosion. Proper preparation and application technique will deliver long-lasting protection for vulnerable underbody components. Careful attention to seams, enclosed areas, and multiple coats ensures comprehensive coverage. Keeping your vehicle rust-free with a high-quality barrier spray greatly reduces the need for expensive rust repair down the road.

Rust Barrier Brand Price Protection Length Key Features
Fluid Film $10-20 per 11 oz can 1-2 years Lanolin based formula, goes on thin
Corrosion Free $25-40 per 32 oz bottle 2-3 years Rubberized coating, waxy finish
Rust Bullet $50-100 per quart 5+ years Industrial strength, bonds to metal

This table summarizes some top-rated rust barrier products, their typical cost, expected longevity, and key characteristics. Prices vary based on quantity purchased.