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How to Remove Rust From Your Truck or RV Undercarriage

How to Remove Rust From Your Truck or RV Undercarriage

Is your older RV or truck getting rusty underneath? If you are not sure, it’s a good idea to take a look because excessive rust can destroy your vehicle.

If you haven’t faced this problem before, don’t respond too quickly. There are several ways to get back on the road. But they all depend on the extent of the rust issue. Here, we lay out how to remove rust from a vehicle’s undercarriage before throwing in the towel on your dream.

Can Undercarriage Rust Be Fixed?

If you have an older truck or RV, there’s a good chance there may be some rust, at least on the undercarriage. It can slowly eat away at the vehicle’s frame, permanently damaging it. But if you catch the rust early, you can usually stop its forward progress and save the vehicle’s structure.

How to Remove and Paint Undercarriage Rust Using Krud Kutter

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 this chemical reaction between oxygen and iron. 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. 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.

Mechanic removing rust from undercarriage of vehicle
The severity of the rust will determine how you remove and repair the damage.

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.

How Do I Keep My 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.

Fluid Film (3 Aerosol Cans) Rust & Corrosion...

➡ 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, are prone to rust.

Which Rust Remover Is Best? 

For bolts and smaller parts, the best rust remover is WD40 Specialist 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.

Rust-Oleum 300112-6PK Rust Dissolver, 32 oz (6...
  • Easy to use spray gel that clings to iron, steel and other metals...
  • Contains a rust inhibitor that continues to protect metal from...
  • Dissolves medium to light rust in 10 to 30 minutes or less,...

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.

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...

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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Tom & Caitlin Morton of Mortons on the Move gave up the stationary life for one where they are constantly on the move. They are full-time travelers, television hosts, and digital media producers.
They left their jobs, sold their house and possessions, and hit the road in September 2015 in their full-time “home on wheels”. Since then they have traveled the US, Canada, and even internationally by RV.
Now, they are Discovery Channel & PBS TV Co-stars of The RVers, producers of “Go North” on Amazon Prime, co-founders and instructors of RV Masterclass, and contributing authors for and an Arizona travel guide.

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