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How to Remove Rust From Your Truck or RV Undercarriage

We like to buy used vehicles, but this means that they usually have a few miles on them and some rust. While surface rust does not necessarily signify a problem, it can be unsightly and cause damage if allowed to get too bad. I usually inspect my vehicles once a year and look them over for areas where rust needs to be corrected. Heres how we recommend tackling this problem.

Can Undercarriage Rust Be Fixed?

While it’s usually possible to stop undercarriage rust, the damage it has done cannot be reversed without adding new metal. If caught early enough, however, it’s usually just surface damage, and it can be stopped. This can be done by removing the rust, treating and painting, or by applying a coating that can slow the progress of existing rust.

How To Keep Your RV or Truck From Rusting? 

Many dealers offer to apply a moisture-proof barrier on the undercarriage when purchasing a new vehicle. But for older RVs and trucks, you can still be proactive, washing them in the winter if you live in a region that uses salt to keep ice from forming on the roads. The simple formula of “moisture + salt + iron = rust” is at work every winter.

Adding a coat of rust preventative before every winter is one of the best ways to prevent rust. A combination of an oil and wax will provide the best preventative that will stick to the frame. We personally like paraffin mixed with linseed oil. You can also use a dedicated rust preventitive product like Fluid Film You can get into all of the nooks and crannies of your truck or RV frame. When applying these products its essential not to get them on the vehicle’s brakes or it can cause malfunction.

Even if you do not apply paint, fluid film will coat the rust and seep in to slow or stop the spread. This is something that needs to be applied at least once a year on rusty surfaces.

Fluid Film (3 Aerosol Cans) Rust & Corrosion...
  • STOPS RUST & PROTECTS METAL ON THE SPOT. THIS NOT A OIL. IT A...
  • CONDITIONS Leather, VINYL & WOOD
  • FLUID FILM WILL NOT BURN GREENERY WHEN USED IN TRIMMERS

➡ RV frames are made of different materials, and some are more resistant to rust than others. Here’s What You Need to Know About RV Frames.

Rusted Class A Motorhome
RVs, especially those made with steel frames (almost all of the), are prone to rust.

How Do You Remove Rust From the Undercarriage of a Truck or RV? 

There are several options when it comes to removing rust from the undercarriage. To decide on the right one for your RV or truck, you should first inspect it to discover the extent of damage. If there are just a few spots, you can most likely take care of them with a bit of sanding.

Using abrasive sandpaper or a grinding wheel, take off the rust. Then treat the affected areas with a corrosion-inhibiting primer or an oil-based rust-proofing spray that will seep into all the connections and cracks of the undercarriage.

If the rust is located in a difficult place to remove it physically, you may want to use a chemical rust remover like Corroseal Water-Based Rust Converter. It won’t only break down the rust, but it will also leave a primer that will protect the frame from rust in the future.

Corroseal-82320 Water-Based Rust Converter Metal...
  • Paint, prime and convert rust in one step - water based rust...
  • Restore metal surfaces, extend life of metal equipment by...
  • Non-flammable and non-corrosive, water-based formula cleans up...

If the damage is significant, you may have to remove rust from major portions of the undercarriage. This could be done with wire brushing or sandblasting. Since this frame is the primary support for the vehicle, those missing pieces may make it structurally weak. Any structural section that has rusted through should be inspected by a professional.

The Hitch on our rusting out truck
Yep that was the hitch on our farm truck, this had to get replaced and other parts of the frame welded up

Finally, if you find that the vehicle frame has gaping holes that will affect the structural integrity of the undercarriage, it will require welding or a complete replacement. We have had to weld up a few severely rusted frames in the past to make sure they were safe to drive.



Which Rust Remover Is Best? 

For bolts and smaller parts, we recommend CRC Evapo-Rust Remover Soak. It’s extremely effective in removing rust from any type of surface but it requires submerging the part in the solution. It does, however, have a strong odor, but the mixture is biodegradable and non-toxic.

CRC Evapo-Rust, Heavy-Duty Rust Remover, Reusable,...
  • EVAPO-RUST RUST REMOVER: Evapo-Rust effortlessly removes rust...
  • SAFE TO USE: This metal rust remover is made of a water-based...
  • VERSATILE: The non-corrosive rust remover can be used to remove...

For paint on rust removal, we recommend using a product with a phosphoric acid base. A product like Krud Kutter a must for rust or FDC Rust converter. These products convert the rust to a paintable surface that will slow further rusting.

Sale
FDC Rust Converter Ultra, Highly Effective...
  • CONVERT RUST: Convert rust to an inert coating that seals out...
  • SAFE TIME & MONEY: Eliminates the need for sandblasting, grinding...
  • EFFICIENT: 1 Gallon Covers 500 square of smooth, nonporous...
How to Remove and Paint Undercarriage Rust Using Krud Kutter

What Removes Surface Rust?

You can usually remove surface rust on truck and RV frames with heavy grit sandpaper or a grinder. An angle grinder with a twisted carbon steel wire wheel is our personal favorite. Be sure to wear eye and hand protection when operating a grinder, however.

HOYIN 4Inch Wire Wheel Brush, Twist Knotted,...
  • Feature: 0.020in normal carbon steel,1/2 in. face width, 7/8 in....
  • Fits: 4 in. and 4-1/2 in. angle grinders Rugged knot...
  • Handles: old greasy build up, precision deburring, rust, spatter...

If the rusted area is small and not too deep, you may even want to try a chemical rust remover like Rust-Oleum’s Rust Dissolver

Removing rust from vehicle with sandpaper
Heavy grit sandpaper can remove surface rust.

Will Painting Over Rust Stop It?

If spots of rust are forming on your vehicle, putting paint over the rust can actually stop it from progressing. It just has to be the right type of paint. Most paints used on rusted metal are only applied after removing the rust. Those paints fall in a category entitled “rust preventing paint.” A coat of this paint will keep rust from returning after its removal.

The second category of paint – rust neutralizing paint – can be used directly on top of the rust. It reacts with the rust to create a stable coating on the metal. Many use it on surfaces where the paint color is not an issue. This is because the neutralizer will change the existing color on whatever surface it is applied. The category may also be referred to as rust converters.

➡ Painting your RV for the first time? Get our top tips here: RV Exterior Paint 101: How Do You Paint the Outside of Your RV?

Is Removing Rust From Your Truck or RV Undercarriage Worth It?

Unless your RV or truck has large chunks of rust that ate through your vehicle’s frame, it’s probably well worth investing the time and effort into removing and repairing the undercarriage.

Granted, it can be expensive to hire a welder to make a frame structurally sound again. Still, if the vehicle is in good shape, it would be less costly than buying and installing a new frame or purchasing a new vehicle altogether. 

rust on truck camper
If the rust is minor, it’s worth tackling the removal yourself.

If the rust spots are small, you can easily manage the removal and expense. On the plus side, once you treat the rust, you’ll protect the frame from future occurrences. So it might prove wise for you to learn how to remove rust from the undercarriage today in case you run into a rusty situation in the future.

RUST can destroy your RV. Here's how to fix it 👍

Is your RV suffering from delamination? There’s a fix for that too! Learn How to Stop and Fix Delamination on Your RV.

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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Carl

Saturday 16th of March 2024

I've just swapped to spraying all spots that are bare with cold galvanizing compound spray paint. After going over it, I use fluid film over it all. Next year, there may be some spots that were scraped or rust flaked off. I'll coat again with galvanizing paint and fluid film again. I won't use any solid film primers, paints, or undercoating as it seems like they lock any moisture inside and flake off when the rust builds up.

Tom and Caitlin Morton

Wednesday 20th of March 2024

I think your right, and yes, if it cannot be completly cleaned, it will just rust again, so convert or prevent it!

Chazman

Saturday 16th of March 2024

Woolwax - just like Fluid Film, but without the stank. Great stuff.

Tom and Caitlin Morton

Wednesday 20th of March 2024

Thanks for the recommendation, will give it a try!