As long as vehicle body panels are made from steel, they’re going to rust. If you ignore rust spots on your car, they’ll spread and turn your sheet metal into Swiss cheese in no time. Sooner or later, rust on cars is inevitable. However, if you deal with rust early, you can stop it from spreading and squeeze a few extra years out of your vehicle.
Rust repair isn’t hard, but it is time-consuming (mostly waiting for primer and paint to dry between steps). Plan to spend about $100 on supplies like sandpaper, primer, masking tape, poly sheeting, a tack rag, polishing compound, and touch-up paint and clear coat. Choose a calm, overcast day and block out the full day to fix the most common rust spots on the hood and doors.
How Does Rust Occur?
Rust is impossible to avoid since it’s a natural chemical process that occurs when iron, a core component of steel, comes into contact with moisture and oxygen. The earth’s atmosphere has plenty of water and oxygen to spare, making it a common element of our ecosystem. Any steel exposed to the air will eventually corrode due to a process called oxidation.
However, some types of steel take longer to corrode than others. Furthermore, modern cars are manufactured with far more durable galvanized steel, a corrosion-resistant material.
Your car’s paint also plays a pivotal role in preventing rust damage. It physically prevents oxygen and water from coming in contact with the steel beneath its surface.
Generally speaking, as long as you regularly wax your car and take care of it, you probably won’t have to worry much about rust. But if you have an old car you want to fix up, or your vehicle has accumulated rust from being left outside for months, there are ways you can repair the corrosion without replacing the steel wholesale.
What You’ll Need to Fix Rust
If you want to fix significant rust spots, you’ll need specific tools that are critical to getting the job done. These include:
- First, find the car manufacturer’s paint code.
- Note: The paint code can be in a variety of places on the body, in the engine compartment or trunk, or in other places. Use either of these online resources to find instructions on how to locate your paint code: automotivetouchup.com or duplicolor.com.
- Buy automotive touch-up paint in pints and quarts to use in a spray gun, in aerosol cans, or in roller ball applicators.
- Pro tip: Even if you know how to use a spray gun, mixing automotive paint with a reducer to match the temperature and humidity conditions can be mighty tricky. We don’t recommend it. Instead, buy aerosol cans for larger repairs and rollerball applicators to fix scratches.
- Note: Most late-model vehicles were painted with base coat/clear coat paint. The base coat contains just the pigment and binding resins-the clear coat is just the gloss.
- Buy equal amounts of both base coat and clear coat.
- You’ll also need an epoxy self-etching primer to bite into the bare metal and a lacquer primer to hold the paint.
- Buy 40-, 600- and 1,000-grit sandpaper, a sanding block, grease and wax remover, poly sheeting, painter’s tape, a tack rag, and a microfiber cloth.
Don’t forget safety equipment! You should always use safety goggles, gloves, and a respirator or surgical mask at a bare minimum when performing rust removal.
Prepare Your Car
Once you have gathered all your materials, you’ll need to prepare your car for rust repair.
To do this, start by bringing your car to a suitable location for the task, like an outdoor space or the interior of a clean garage. Pick a place where other objects won’t get dirty as you sand away rust and paint.
After deciding upon a suitable location, the real work begins. Start by covering every non-rusty inch of your car’s surface. You don’t want to accidentally sand down any of the good paint or wax on your vehicle. You can cover your vehicle with a material like newspaper, for instance. Simply use the masking tape mentioned above to secure the newspaper (or any other covering solution) to the surface of your car.
If you plan to use an angle grinder to get rid of a significant amount of rust, consider utilizing a fire-resistant and durable protective covering for your car – since sparks will be flying in the immediate area.
How to fix rust on a car: Step-by-step instructions for car rust repair
1. Remove the Rust
- Crack off any blistered pint with a scraper.
- Sand through the rust spots down to the bare metal, using 40-grit sandpaper.
- Enlarge the sanded area so you’ll have space to feather the edges.
- Switch to 120-grit sandpaper to feather the edges of the repair area.
- Complete the feathering with 220 grits.
- Use a tack rag to remove particles from the unmasked area.
2. Clean with Detergent
- If the rust has created pits in the metal, you can fill them now with body filler or wait until the epoxy primer dries and apply multiple coats of filler primer.
- Clean the entire unmasked area with a grease-cutting dishwashing detergent, followed by clean rinse water.
- Let it dry.
- Wipe the area with a lint-free cloth to remove any remaining dust or lint.
- Apply the paint manufacturer’s prep solvent.
3. Apply Epoxy Primer, Then Filler Primer
- Spray the filler primer in heavier coats to cover the entire repair area.
- Move the can away from the surface slightly and blend it into the surrounding painted area.
- Pro tip: Self-etching epoxy primer provides a strong bond to bare metal, so use it as your first coat.
- Spray two to three medium coats, allowing the recommended wait time listed on the label (usually 15 minutes) between coats.
- Wait a full hour for the epoxy to dry to the touch (longer if it’s humid outside).
4. Sand the Primer
- Starting with wet 600-grit sandpaper, smooth the primer and feather the edges.
- Switch to wet 1,000-grit sandpaper to final sand the entire repair, including the blended areas.
- Wash with clear water and let dry.
- Wipe the dried epoxy primer with a lint-free cloth.
- Apply two to three heavier coats of lacquer filler primer, allowing drying time between each coat.
- Let the lacquer primer dry until it’s dry to the touch—at least one hour—before sanding.
- Sand drips and sags with 320-grit sandpaper.
- Then final-sand the entire repair area.
5. Apply the Colored Base Coat
- Holding the spray can about 12 in. away from the surface, spray the repaired area.
- Start at the bottom of the repair and apply the color coat in left-to-right rows, overlapping each pass by about one-third.
- Build the color slowly into the repair and surrounding areas in two to three coats.
- Allow about 10 to 15 minutes between coats.
- Allow the base coat to dry, until it’s dry to the touch, at least 60 minutes.
- Pro tip: Don’t sand the base coat (especially metallic colors) unless you’ve created sags. In that case, sand lightly and then respray the touched-up areas.
6. Spray on the Clear Coat
- Apply several coats of clear coat, allowing the recommended drying time between coats.
- Gradually work the clear coat into the surrounding painted areas to achieve a smooth blend line.
- Note: This is the hardest part because all clear coats run easily and that will ruin the look of your paint job. If you create a run in the clear coat, you’ll have to let it dry for at least 48 hours before attempting to fix it with fine-grit sandpaper and polishing compound. Then you’ll have to respray the sanded area. So, practice spraying on a scrap piece of cardboard to get a feel for the nozzle and the speed of application.
- Let the clearcoat dry for several hours before driving the vehicle and at least 48 hours before buffing.
7. Finishing up
- Using an old cotton T-shirt or microfiber cloth and buffing compound, hand-buff the repaired area.
- Pro tip: Don’t use a polishing machine for this step. Wait at least 30 days before waxing.
How to Remove Surface Rust
- Start by cleaning the affected area and let it dry completely.
- Mask off the area you want to work on using the painter’s tape.
- Spray the rust remover onto the rusty spot and let it sit for around 10 minutes.
- Next, wipe off the residue using a microfiber cloth. Most, if not all, of the rust, should have come out by now. If there’s any leftover, sand it using the sandpaper and wipe off the residue.
- Clean the affected area using the grease remover soap and let it air dry thoroughly.
- Spray 3 light-to-medium coats of the primer allowing each layer to dry for 1 hour.
- Spray 5-6 coats of your car’s color base coat. Ensure that each coat is thinner than the primer coats and allow enough drying time between the layers.
- Finish by spraying the clear coat and wait for at least 2 days before washing the vehicle and 2 months before waxing.
How to Remove Scale Rust
Begin by marking off the part with rust. You may want to cover the entire vehicle except the work area to protect the unaffected parts from the fine dust from the sander.
- Attach a sanding wheel to the grinder to remove the surface rust.
- Use the grease and wax remover soap to clean the area you’re working on and let it dry completely.
- Fill any depressions and holes left with a fiberglass-reinforced car body filler.
- Sand the work area starting with the 40-grit sandpaper followed by the 320-grit and lastly the 2000-grit sandpaper. After sanding, clean the area using the wax and grease remover soap.
- Use the painter’s tape to tape off the area for painting.
- Start by spraying 3 light-to-medium coats of primer waiting for the layer to dry before applying another.
- After the primer, spray around 5 coats of your car’s paint leaving enough drying time between the layers.
- Lastly, spray 1-2 layers of clear coat. Wait for at least 2 days before washing your car and at least 2 months before waxing.
Yes, car rust can be stopped from spreading. However, the ideal fix will depend on the type of rust. Surface and scale rust can be stopped by sanding the rusty paint and spraying primer, color coat, and clear. On the other hand, penetrative cost requires replacing the entire panel or cutting the rusty part, and welding a new patch.
It depends on the severity of the rust. Surface and scale rust problems are easy and inexpensive to fix. However, if the vehicle has several areas that have rusted to the extent of having small holes through the panels or frame, the cost of fixing these rusty spots may be equal to that of buying another car. Consider the costs and make the decision.
Yes. Given enough time, rust can ruin your car to the point of no repair. Penetrating rust can weaken vital components compromising your safety and that of your passengers and other road users.