Rust on car runners, also known as rocker panels, is a common problem, especially in areas with harsh winters or coastal climates. If you’ve noticed rust developing on your car’s runners, it’s crucial to address it promptly to prevent further damage and maintain your vehicle’s structural integrity. While professional repairs can be costly, tackling rust repair yourself is a viable option with the right tools and know-how. This guide provides a detailed, step-by-step approach to repairing rusted runners, empowering you to restore your car’s appearance and protect it from further corrosion.
Before diving into the repair process, it’s important to assess the extent of the rust damage. Minor surface rust can often be treated relatively easily. However, if the rust has penetrated deeper, causing holes or significant weakening of the metal, more extensive repairs will be necessary. In severe cases, as mentioned by some repair estimates, replacing entire sections might be recommended, although this is often deemed uneconomical for older vehicles. For most DIYers, focusing on repairing existing rust and patching holes is a more practical approach.
This guide focuses on repairing rusted runners using common DIY methods, drawing upon expert techniques for effective and lasting results. We’ll cover everything from rust removal to patching holes and finishing for a professional look.
Step-by-Step Guide to Repairing Rusted Car Runners
1. Rust Removal: Preparing the Area
The first and most critical step is to thoroughly remove all rust from the affected area. This ensures that the repair is long-lasting and prevents rust from spreading beneath your new paint or filler.
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Initial Scraping: Begin by using a scraper, putty knife, or flat-head screwdriver to remove loose rust flakes, paint chips, and scale. Work on both sides of the runner panel if accessible to check for rust-through. Remove all loose rust on both sides.
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Dealing with Rust-Through: If you encounter holes, it indicates rust-through. You’ll need to remove the weakened, rusted metal around the holes. Use tin snips or a drill with a coarse file to carefully cut away approximately 1/8″ to 1/4″ of metal surrounding each hole. This ensures you’re working with solid metal for patching. Smooth the edges with pliers, removing any kinks from the tin snips, and be careful not to scratch surrounding good paint. For very small pinholes, extensive cut-out might not be necessary.
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Aggressive Rust Removal: Complete rust removal is crucial unless you are using a specialized paint designed to go directly over rust (like POR-15). Avoid rust converter primers as they are often less effective. Use 60 or 80 grit sandpaper or a wire brush (wire brush followed by sandpaper is often most effective) to aggressively clean the metal areas exposed in the previous steps. Work on both sides of the panel if needed. Sand until you see shiny, bare metal. Scrape again to ensure the metal is solid and not just a layer over rust. Continue sanding and scraping until you reach solid, shiny metal throughout the rusted area.
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Feathering the Edges: Once the rust is removed, switch to finer sandpaper (150-220 grit). Gently sand and feather out the edges into the surrounding good paint. This creates a smooth transition and prepares the area for primer and paint, allowing for better blending. You should be able to see the layers of paint – bare metal, primer, color coat, and clear coat – as you feather outwards.
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Cleaning and Drying: Thoroughly clean the sanded area with soap and water using a plastic brush to scrub away dust and debris. Dish soap works well. Dry the area completely.
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Rust Remover Application (Optional but Recommended): For pitted areas where sandpaper can’t reach, use a rust remover compound. Naval Jelly (phosphoric acid) is a readily available gel that works effectively and stays in place. Follow the product instructions carefully and apply it to the affected areas. Avoid getting rust remover on undamaged painted surfaces; use masking tape and paper to protect these areas if needed. Naval Jelly leaves a white powdery residue after washing off, scrub this away with a plastic brush or sandpaper to reveal the metal underneath. Use clean 100-150 grit sandpaper between applications to ensure no rust is hidden beneath the surface. Complete rust removal is vital to prevent rust from reappearing under the new paint.
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Final Sanding and Drying: After all rust is removed, do a final sanding with clean 150-220 grit sandpaper. Clean the area again with soap and water, and dry thoroughly. Use a heat gun or hair dryer to ensure complete dryness and allow the surface to cool before proceeding. Don’t delay priming too long as bare metal will start to oxidize (surface rust) almost immediately.
2. Patching Holes in Car Runners
If rust removal has revealed holes in your car runners, patching them is the next step to restore structural integrity and create a smooth surface for finishing.
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Fiberglass Patching (Common DIY Method): Fiberglass patch kits are widely available at auto parts stores and are a common and effective way to patch holes. The exact procedure can vary slightly depending on the kit, so carefully read and follow the manufacturer’s instructions. Patching is typically done from the back side of the panel. Minimal surface preparation is needed beyond cleaning the area with a light solvent like alcohol.
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Applying the Patch: Ensure the patch doesn’t protrude beyond the surface of the surrounding metal on the outside of the panel; this will create a hump that’s difficult to smooth out. Allow sufficient curing time for the fiberglass patch according to the kit instructions before moving to the next step.
3. Filling Dents and Smoothing the Surface
Whether you have dents from impacts or patched holes, body filler is used to create a smooth, even surface ready for priming and painting.
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Metal Hammering (If Necessary): If impact damage has caused metal to protrude outwards, gently hammer it back into shape before applying filler. A body hammer or a regular hammer with a wooden block can be used. It’s easier to fill a slight depression with filler than to shave down excess metal.
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Applying Body Filler: Polyester body filler (like Bondo) is commonly used and relatively easy to work with. It requires mixing with a hardener to cure. Read the instructions carefully for proper mixing ratios. Apply the mixed filler to the dented or patched area using a putty knife, slightly overfilling the area. Allow it to cure completely. The curing time for Bondo is consistent regardless of thickness (when mixed correctly).
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Shaping and Sanding the Filler: Once the filler is cured, begin sanding with 100-200 grit sandpaper to shape it and bring it close to the level of the surrounding panel. Be careful not to sand into the surrounding primer if you primed earlier. For larger areas, a long straight edge (like a framing square or level) can help ensure a flat surface. As you approach the desired level, switch to progressively finer sandpaper. Use 300 grit wet sandpaper to achieve a smooth transition and blend the filler seamlessly with the panel. A flat, sharp file can be used carefully to remove high spots, or use sandpaper wrapped around a hard wooden block.
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Spot Putty for Minor Imperfections: For very small gaps or imperfections after the initial filler sanding, use spot putty. Apply it to fill these minor areas, allow it to cure, and then wet sand with 300 grit sandpaper to create a perfectly smooth surface.
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Final Cleaning: Wipe down the entire repaired area with a clean cloth and water to remove sanding dust and prepare for priming. Dry thoroughly.
4. Priming, Painting, and Finishing
With the rust removed, holes patched, and surface smoothed, the final steps involve priming, painting, and clear coating to protect your repair and blend it with the surrounding car finish. Refer to automotive painting guides for detailed instructions on achieving a professional paint job, focusing on proper application techniques, paint compatibility, and safety precautions.
Maintaining Your Runners and Preventing Future Rust
Once your runners are repaired, taking steps to prevent future rust is essential for long-term protection.
- Regular Cleaning: Wash your car regularly, paying special attention to the runners and undercarriage, especially during winter months when salt and road grime are prevalent.
- Rust Prevention Sprays: Apply rust inhibitor sprays or coatings to the runners, especially in vulnerable areas.
- Touch-Up Paint: Promptly address any paint chips or scratches to prevent rust from starting.
- Undercoating: Consider applying undercoating to the undercarriage and runners for added protection, especially in rust-prone areas.
Repairing rusted car runners is a manageable DIY project that can save you significant costs and extend the life of your vehicle. By following these steps and taking preventative measures, you can effectively combat rust and keep your car looking its best.
