All cars rust sooner or later. Anything made of steel, which contains iron, eventually rusts. Knowing what to do when you notice rust on your car can be challenging.
Read on for a definitive guide to automobile rust, what to do about it, and how much rust is too much on a car.
How Does Rust Develop?
Rust forms when iron or a material containing iron has prolonged contact with moisture. The atoms react, resulting in oxidation, known as rust.
The three most likely ways your vehicle will develop rust are weather exposure, road salt corrosion, and neglect.
Weather Exposure
All vehicles will experience some precipitation whether they are garage-kept or not. Protecting your vehicle from rain and snow whenever possible helps reduce your chances of rust.
Rain and melting snow can find their way into crevices where they cannot evaporate quickly. Inside the door frame, wheel wells, and the underside are the most likely places for rust to develop.
It's impractical to dry off the undercarriage, but you could towel off the rest of your car after a storm. Focus on those problem areas like inside the doors, hood, and trunk. Anywhere you notice water pooling is a good place to towel dry.
Salt
In many areas, the Department of Transportation uses road salt to melt ice on the roads. You might also use salt on your driveway to help clear snow and ice.
The salt has a corrosive property that makes the paint and metal on your car more vulnerable to oxidation (rust). The brake and fuel lines are particularly susceptible to road salt corrosion because they are made of metal and close to the undercarriage.
Neglect
Regular maintenance on your car is the key to solving many problems before they become disasters. Check for rust regularly and wash off road salt periodically through the winter.
How Fast Does Rust Spread?
Rust can become a huge problem right under your nose, especially if you neglect regular maintenance for your vehicle. How fast rust spreads depends on several factors.
Cleanliness
When dirt and road salt clings to the metal on your car, they create the potential for rust. They weaken the metal and allow moisture to stay in contact with the metal for an extended time.
A dirty vehicle will rust more quickly than one that is kept clean.
Contaminants In The Metal
Pure iron rusts more slowly than an alloy. An alloy is a mixture of metals. Car manufacturers use alloys for the cassis because pure iron is not flexible enough to mold into the shape needed to make your car. Therefore, alloys solve one problem (flexibility) while creating another (rust).
The closer your cassis is to pure iron, the more slowly it will rust.
Type Of Rusting
Some forms of rust on your vehicle spread faster than others.
Surface Rusting
Surface rust happens when your paint is scratched, chipped, or peeling. The exposed metal may begin to rust, and that rust can spread quickly.
Dealing with surface rust is easier than other kinds. Usually, surface rust does not penetrate the metal unless it is an iron alloy.
Scale Rusting
Unfortunately, by the time you notice scale rusting, you have a huge problem on your hands.
The thickness of the metal factors into the speed of scale rusting. The body is made of thin metal, so bubbling and flaking rust on the body spells trouble. Rust on the cassis will spread more slowly because it is heavy metal.
Scale rusting also spreads faster in iron alloys than in pure iron. Jump on scale rust as soon as you notice it to prevent it from proceeding to the final stage: penetrative rusting.
Penetrative Rusting
The final stage of rust is penetrative rusting. Oxidation corrodes the metal so deeply that holes form. This is irreparable damage to that section of your car. Replacing a panel or section of a panel is the only way to repair penetrative rust.
It can take years for rust to totally penetrate the metal, so repairing it at the first signs is the best way to prevent worse damage.
Can You Fix Rust Yourself?
Bodywork is among the most expensive repairs to make on a car. We all love to make space in our budgets with a DIY repair when possible.
Whether you can repair a rust spot on your own depends on the extent of the rust and where it is.
Small spots of surface rust are simple to repair for less than you'll spend at a body shop. Supplies to fix small rust spots cost about $100.
What You'll Need
- Sandpaper
- Primer
- Masking tape
- Poly sheeting
- Tack rag
- Polishing compound
- Touch-up paint
- Clear coat
The process is straightforward but time-consuming. You'll spend a lot of time waiting for layers of primer, paint, and clear coat to dry.
An overcast day with no precipitation is the best weather condition for these repairs.
Prep the Repair Area
- Scrape off blistered paint
- Sand the rust spot down or bare metal with 40-grit sandpaper.
- Broaden the sanded area to feather the edges and create a smooth repair.
- Use 120-grit sandpaper for feathering the edges of the work area.
- Switch to 220-grit sandpaper to finish the feathering.
- Remove particles with a tack rag.
Clean and Fill in Pits
- Use body filler or epoxy primer to smooth out pits left by the rust and let it dry.
- Clean the repair area with grease-busting dish soap like DAWN.
- Rinse with plain water and let the area dry.
- Wipe the repair spot with a lint-free shop towel.
- Apply the paint prep solvent.
Apply Primer
- Spray on 2-3 medium coats and allow the recommended try time between the coats listed on the label.
- Hold the spray can further away than when you filled in the pitting in the last step. Now you want to blend the edges into the surrounding paint.
Sand The Primer
- Use wet 600-grit paper to smooth the primer and feather the edges.
- Move to wet 1000-grit paper for final smoothing and feathering.
- Wash the area with clean water and let it dry.
- Wipe the area with a lint-free towel.
- Apply 2-3 heavy coats of lacquer primer and allow dry time between coats.
- Sand the repair area with 320-grit paper.
Paint The Area
- Apply the colored base coat by starting at the bottom of the area and moving left to right. Overlap your rows with each pass by about one-third width.
- Use 2-3 coats and allow drying time between each (about 15 minutes)
- Allow the last base coat to dry for about 60 minutes.
- Apply several layers of clear coat, gradually working into the surrounding area.
- Allow several hours for the clear coat to dry before driving.
- Do not buff for at least 48 hours.
Can You Prevent Rust?
Rust is one of the worst problems you can have with your vehicle. It grows and spreads like a living thing and can be expensive to remedy.
If you live in a state with required vehicle inspections, your inspector will check for rust at that time. Otherwise, checking your vehicle for rust should be part of your summer maintenance schedule.
There are some ways to prevent rust from becoming a serious problem during the life of your vehicle.
Wash Your Car
Dirt and road salt on your car compromise the protective clear coat and paint on the body and the undercarriage. Regularly washing your vehicle with the underneath and the wheel wells helps prevent rust spots.
In winter, you should at least rinse your car once a week.
Check Your Paint
The paint is the main protectant from rust forming on your car's body. Perform a visual inspection at least annually. Look for spots with peeling or chipping paint.
You can touch up trouble spots in your paint yourself or visit a body shop.
Wax Your Car Twice Per Year
Wax gives your car a beautiful shine and protects the paint job. As the paint protects the metal body, the wax forms a barrier between the paint and moisture.
The easiest way to ensure you wax your car twice annually is to have it detailed. A professional will deep clean the interior, wash, and wax your vehicle.
Clean Your Interior
Clean up spills when they happen. Liquid seeps through the carpet to the floor. When it contacts metal, it creates a potential for rust.
Is Rust Dangerous?
Rust is dangerous because it compromises the strength of the metal used to build your vehicle. It can take years for rust to endanger your safety and most car owners notice it before it is this extreme.
When Should I Worry About Rust?
As soon as you notice rust, you should work towards repairing it yourself or taking it to a body shop. The key to dealing with rust is taking care of it before it spreads or penetrates deeper into the metal.
How Much Rust Is Too Much On A Car?
Small patches of surface rust are fairly easy to deal with. Deep rust that wears holes in the metal is too much and requires serious repairs to keep your vehicle on the road.
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