When you bought that new car 10 years ago, you vowed it would look brand-new forever. But sometimes car maintenance gets tossed on the back burner amid everyday life. Next thing you know, your car's showing signs of wear you never expected, including rusting.
Fortunately, rust isn't always a serious problem, as there are plenty of rust repair hacks you can do yourself. We'll cover some of these rust repair processes below, plus explain what causes rust and what you can do to prevent it in the future.
What Causes Rusting on Cars?
Most cars rust — that's a simple, unavoidable fact. When their steel reacts with various elements, it causes oxidation, which we all know as rust. Let's look at some of the most common causes of vehicle rusting.
Water
While other elements factor into automotive corrosion, water remains one of the most common. Between rain and puddles, our vehicles can encounter serious water contact year-round.
When iron is exposed to water, an atomic reaction causes rusting. This isn't to say that washing your car causes rusting, though. The surfaces you wash are protected by paint, so the water never has the chance to interact with the bare steel long enough to cause rusting. Rather, washing your vehicle eliminates the small dust particles and other debris on your paint job that can cause scratches and expose the bare metal, which is then susceptible to rusting.
Salt
Salt is another major catalyst for rusting, as it speeds up water's ability to carry electrons, which conducts ions and accelerates rusting. When speaking about salt causing rust, most people think of vehicles driving through salted roads in the fierce Canadian winter.
While that is a leading cause for severe rust spots, it's far from the only way salt impacts your vehicle. In coastal areas — near the ocean or other large saltwater bodies — the salt water can also accelerate rusting. In fact, salt water corrodes steel five times faster than fresh water.
What's more, you don't need to drive through the ocean for it to cause corrosion on your car. Sea spray and salty ocean air can have the same impact as direct contact with the water. Plus, ocean water bacteria consume iron and their excretion turns into rust.
Neglect
Neglect is the final piece of the puzzle to surface rust and rust holes in your car, as water and salt themselves can't immediately cause rusting. The rust damage comes from not properly maintaining your vehicle.
Periodic pressurized undercarriage and body cleaning is a critical step in rust prevention. This clears the area of any salts left behind from the roads or salty ocean water, preventing rust from even appearing.
Most car washes offer optional pressurized undercarriage-cleaning services. You should use these services after each season for the best results.
Why Cars in the North Tend to Rust Faster
Drive around Quebec or most other cities in Canada and you'll find more severely rusted vehicles than you may in the south. This is generally due to road salts.
Local governments commonly use large salt rocks to melt snow and ice. While this is very effective to keep roads safe, the salt accelerates rusting. This is why you often see so many rusted vehicles in Quebec and throughout Canada.
Common Rust Trouble Spots
A car can rust wherever there is steel, which is the vast majority of the vehicle. However, there are some areas where rust spots are far more common than others. Let’s explore these areas and why they're so susceptible to rust.
Undercarriage
A vehicle's undercarriage — the floorboards, wheel wells, frame, and suspension — takes the brunt of the salt and water from the roads. It also rarely gets a good cleaning.
Honestly, when's the last time you crawled under your car and pressure-washed it?
Not having a good pressure wash along with the sheer amount of exposed metal under your vehicle can cause massive rusting issues.
Rocker Panels and Wheel Flares
Your rocker panels are the lowest point of the body under the doors, and the wheel flares are the lowest point on your fenders and quarter panels. Being the lowest point on the body makes them one of the first contact points for salt and water. Plus, they curve under the vehicle, leaving a flat spot for salt and water to accumulate.
This is the perfect storm for rust, which is why it's so common to see cars driving around with the area under their doors and the base of the fenders and quarter panels completely rusted out.
Trunk
The trunk is another common place to find rust. Over time the trunk seal can weaken, allowing water to leak inside. In the center of most trunks is the spare tire compartment — a recessed area for the spare tire to sit. This is prime real estate for water pooling.
Unless you're always getting flat tires, you may never notice this pooling, as it's under the carpeting and spare tire cover. However, this pooling can cause severe rusting and can even lead to rust holes.
Surface Rust vs. Structural Rust
While all rust is pretty much the same, there are two dramatically different levels of rusting: surface rust and structural rust.
Surface Rust
Surface rust is when oxidation occurs only on the top level of the metal. This is typically very early in the rusting process, and a body shop can quickly fix it with sandpaper and rust-sealing paint. The shop will simply sand the rust from the surface, apply a sealing paint to prevent the rust from reoccurring, then prime and repaint the area.
Surface rust generally has no impact on the vehicle's structural integrity, but it's rather unsightly, as it can cause bubbles in the paint and other blemishes.
Structural Rust
If left untreated, surface rust will eventually turn into structural rust. Structural rust is when the oxidation eats through the entire thickness of the metal, leaving a rust hole in its path. These holes may be small and seem insignificant, but they can negatively impact a car's structural integrity — especially in today's unibody vehicles, where the body and frame are one and the same.
Structural rust becomes even more significant when it happens in the undercarriage. Your vehicle's undercarriage is a critical structural point, and rust holes in this area, including the floor pans, makes it more susceptible to flexing and bending. Also, this is where your seats attach to the vehicle, and excessive rust can compromise the metal surrounding the seat mounts, making them unstable.
Rust Repair Options
Depending on the level of rusting, which component has rusted, and your budget, there are many ways to fix rust. Here are some common DIY rust repair methods.
Sand and Paint Away Surface Rust
If you're dealing with surface rust, you're in luck — it's relatively simple to fix. Using an orbital sander with 250- or 300-grit sandpaper, sand down the area until you are through the rust and have clean, bare metal.
Use 400-grit sandpaper on the orbital sander to smooth out the affected area. After sanding, clean the area with soap and water, rinse it thoroughly, and immediately dry it with a lint-free cloth to prevent flash rusting.
Use masking tape and paper to cover all the areas you don't want to get paint on. Apply a coat of rust-sealing paint to the area to prevent any microscopic rust from spreading, then apply primer, automotive paint, and clearcoat as you like.
For a smoother look, it's best to repaint the entire panel. If you decide to paint a single section of a panel, you’ll likely end up with uneven paint that you need to sand and polish to smooth it out.
Fixing Small Rust Holes
Small rust holes — those that are a quarter-inch in diameter or less — can often be fixed with body filler, commonly referred to as "Bondo." Use a wire brush or drill-mounted wire wheel to remove any heavy rust, then sand down the area just as you would surface rust.
Clean the sanded area with soap and water, rinse it thoroughly, and immediately dry it with a lint-free cloth to prevent flash rusting. Use masking tape and paper to cover all the areas you don't want to get paint on. Apply a coat of rust-sealing paint to the area to prevent any microscopic rust from spreading.
Mix the body filler with its cream hardener per the filler's instructions. Apply a thin coat of filler over the hole and smooth out the filler so it's as even as you can get it with the surrounding metal.
Allow the filler to dry for the amount of time specified in the instructions. Sand the filler with 30- or 60-grit sandpaper on an orbital sander until it's level with the surrounding metal and smooth. Switch to 300- or 400-grit sandpaper to further smooth out the filler.
Apply primer, automotive paint, and clearcoat as you like.
Note: Never use body filler to repair frame or unibody components, as it provides no structural rigidity and will not hold up in a crash.
Fixing Medium Rust Holes
For a medium rust hole — anywhere from a quarter-inch in diameter and larger — grind and sand the area to remove rust from the hole and its surrounding area.
Clean the sanded area with soap and water, rinse it thoroughly, and immediately dry it with a lint-free cloth to prevent flash rusting. Use masking tape and paper to cover the areas you don't want to get paint on. Apply a coat of rust-sealing paint to the repair area to prevent any microscopic rust from spreading.
Mix the body filler with its cream hardener per the filler's instructions. Stick a body patch on the hole as directed by the patch's instructions — some are self-adhering and others require an epoxy. Apply fiberglass-reinforced body filler — sometimes called "tiger hair" or "kitty hair" — onto the patch and overlap slightly with the surrounding metal.
Allow the filler to dry for the amount of time specified in the instructions. Sand the filler with 30- or 60-grit sandpaper or an orbital sander until it's level with the surrounding metal and smooth. Switch to 300- or 400-grit sandpaper to further even out the filler.
Apply primer, automotive paint, and clearcoat as you like.
How to Prevent Rust
Instead of dealing with rust repair, why not prevent it from occurring in the first place? Here are a few easy ways to proactively prevent rusting.
Frequent Car Washes
Washing your car regularly is the best way to prevent rusting. This washes away rust-causing contaminants and any debris that can scratch the paint and expose rust-prone bare metal.
The appropriate intervals between washes is up for debate, but at least once a month is a good rule of thumb. During the winter months — in areas where road salts are common — every two weeks may be better.
Don't forget about waxing the vehicle too. This will add an extra layer of protection to the paint. You don’t need to wax your car during every wash — twice per year is fine.
Undercarriage Cleaning
Your vehicle's undercarriage is one of the most susceptible areas to rust, as it takes on all the debris, salt, and other gunk from the road. When you wash your vehicle, make sure to pressure wash in the wheel wells and on the undercarriage to remove any loose debris.
Even with pressure washing during your normal washes, take your vehicle to a professional detailer to have the undercarriage cleaned at the end of each season. This will get all the hidden debris off and prevent it from causing issues.
Rust-Proofing Treatment
Rust-proofing seals off trouble areas from the effects of salt and water, preventing rusting. Several age-old methods of rust-proofing include drip oil spray, dripless oil spray, and tar-based sealer.
All three methods effectively prevent rust and last at least one year before needing to be reapplied. The drip oil and dripless oil methods last the longest at up to 18 months, though some can last even longer.
A professional can apply these rust-proofing measures for $120-$170, depending on the type of vehicle. You can also pick up rust-proofing chemicals for $10-$15 per can for DIY rust-proofing. Keep in mind that this process may require drilling into your vehicle’s body panels. Gauge your comfort level with this possibility and proceed with caution.
There's also a relatively new rust-proofing measure: electronic rust inhibitors. These components purportedly send electrical currents through your vehicle's sheet metal to prevent the electrochemical reaction that causes rusting.
There's a lot of debate about the effectiveness of electronic rust inhibitors. Plus, they can be pricey at $300-$1,000. Our advice: opt for this new-fangled rust-prevention tool at your own risk.
Here at Clutch, we want you to enjoy your pre-owned vehicle without ever worrying about rust, so we offer a rust-proofing package with our vehicles. This undercoat protection is a one-time spray that doesn't require yearly reapplication.
We back up our undercarriage protection quality with a 10-year undercarriage rust guarantee on all current model year vehicles and a six-year guarantee on all older models. Plus, the guarantee transfers to a new owner if you sell your vehicle.
Get Rust-Free and Stay That Way With Clutch
Want to replace that rusty car instead of trying to fix it? Head to Clutch, Canada's first-ever 100% online car-buying experience, and check out our wide range of quality pre-owned vehicles.
All our vehicles go through a 210-point inspection and reconditioning process before we sell them to ensure they're ready for the road. This process includes checking for rusting issues and making necessary rust repairs.
We also back up all our vehicles sold online with a 90-day or 6,000-km limited warranty. Plus, you get a 10-day risk-free trial period with your Clutch vehicle. If you don't love it within the first 10 days, simply return it for a full refund or exchange it for a new vehicle.
You can get further peace of mind with our available undercoat protection and rust-proofing and the Clutch Protection Plan extended warranty. Combined, these will give you years of worry-free driving. Plus, you get all this without the stress of setting foot in a traditional dealership.
