How to Repair Rusted Running Boards on Your Car: A Comprehensive Guide

Running boards are a practical addition to many vehicles, offering easier access into higher cabs and adding a rugged aesthetic. However, they are also commonly exposed to road debris, salt, and moisture, making them susceptible to rust. Ignoring rust can lead to further structural damage and detract from your car’s appearance. Fortunately, repairing rusted running boards is a manageable DIY project that can save you money and extend the life of your vehicle. This guide will walk you through the process of how to repair rusted running boards on your car, ensuring a durable and professional-looking finish.

Materials You’ll Need for Running Board Rust Repair

Before starting, gather all the necessary materials. Having everything at hand will make the repair process smoother and more efficient. Here’s what you’ll need:

• Wax and Grease Remover: For thoroughly cleaning the repair area and ensuring proper adhesion.
• Fiberglass Filler (Short Strand): A strong, waterproof filler ideal for restoring shape and providing a robust repair.
• Filler Hardener: Essential for activating and curing the fiberglass filler. Ensure you use the correct ratio as specified by the filler manufacturer.
• Mixing Board (Wax Paper over Cardboard): A non-porous surface for mixing filler and hardener without absorption or contamination.
• Applicator: For applying the filler smoothly and evenly.
• 80 Grit Sandpaper: Coarse grit for initial shaping and removing larger imperfections in the filler.
• 180 and 200 Grit Sandpaper: Finer grits for smoothing and preparing the surface for primer.
• Sanding Block: Provides a flat, even surface for sanding, crucial for achieving a professional finish.
• Flexible Rubber Backing Pad: Specifically for curved edges, helping maintain smooth contours during sanding.
• Wire Brush: To clean sandpaper and extend its usability.
• Gloves (Optional but Recommended): To protect your hands from filler and chemicals.
• Etch Primer or Filler Primer: To seal the repaired area and provide a base for paint. Filler primer is generally recommended for body filler work to ensure good adhesion and prevent reactions.
• Masking Paper and Tape: To protect surrounding areas from primer and paint overspray.
• Packaging Paper: A cost-effective masking option that absorbs paint well, preventing flaking.

Step-by-Step Guide to Repairing Rusted Running Boards

Now, let’s get into the detailed steps for repairing your rusted running boards.

Step 1: Cleaning the Area

The first and most crucial step is to thoroughly clean the rusted area. Contaminants like wax, grease, and dirt can compromise the adhesion of the filler.

1. Apply Wax and Grease Remover: Liberally apply wax and grease remover to the rusted area and the surrounding paint.
2. Wipe Clean: Use a clean microfiber cloth to wipe away all traces of grease, wax, and dirt.
3. Allow to Evaporate: Let the area air dry completely. This ensures the surface is perfectly clean and dry before applying filler.

Step 2: Applying Fiberglass Filler

Fiberglass filler is excellent for repairing rusted running boards because of its strength and waterproof nature.

1. Prepare the Filler: Following the manufacturer’s instructions, mix a small batch of short strand fiberglass filler with the hardener on your wax paper mixing board. Drag the filler across the surface while mixing to minimize air bubbles.
2. Apply the First Layer: Use the applicator to apply a thin layer of filler to the rusted area. Focus on pressing the filler into the rust pits and restoring the original shape of the running board. Don’t worry about perfection at this stage; multiple layers can be applied.
3. Work Time: Be mindful of the filler’s work time. Once it starts to harden, it becomes difficult to work with and may not bond as effectively.

Step 3: Sanding and Shaping the Filler

After the filler has fully dried, it’s time to sand it down to the desired shape.

1. Initial Sanding with 80 Grit: Begin sanding with 80 grit sandpaper wrapped around a sanding block. This coarse grit will quickly remove excess filler and start shaping the repair.
2. Shape and Contour: Continuously check the shape from different angles to ensure you are restoring the original contour of the running board. This may take time and patience, especially if you are new to bodywork.
3. Flexible Pad for Curves: For curved edges, switch to a flexible rubber backing pad to maintain smooth contours and avoid flat spots.
4. Address Low Spots: During sanding, you may notice low spots or imperfections. These will need additional filler in the next step.
5. Clean Sandpaper: If the sandpaper gets clogged with filler, use a wire brush to clean it and maintain its effectiveness.

Step 4: Applying More Filler (If Needed)

It’s common to require multiple applications of filler to achieve a perfectly smooth and shaped repair.

1. Clean the Area Again: Before applying more filler, clean the sanded area with wax and grease remover and let it evaporate.
2. Apply Second Layer: Mix another small batch of filler and apply it to any low spots or imperfections identified during sanding. Focus on building up these areas to create a level surface.
3. Drying Time: Allow the second layer of filler to dry completely.

Step 5: Fine Sanding and Priming

Once you are satisfied with the shape and contour, refine the surface for priming and painting.

1. Sand with 180 Grit: Sand the entire filled area with 180 grit sandpaper to remove the coarse scratches from the 80 grit and further refine the shape.
2. Final Sanding with 200 Grit: Finish sanding with 200 grit sandpaper to create a smooth surface ready for primer. This fine grit will ensure a seamless transition and excellent primer adhesion.

Step 6: Final Cleaning and Priming

The final steps involve cleaning the area one last time and applying primer to seal and prepare the surface for paint.

1. Final Cleaning: Clean the repair area with wax and grease remover to remove any sanding dust and ensure a pristine surface for primer.
2. Mask Surrounding Area: Mask off the areas around the repair using packaging paper and masking tape to protect them from overspray. Fold back the tape edge to create a soft edge and minimize hard paint lines.
3. Apply Filler Primer: Apply a light coat of filler primer, followed by 2-3 medium to wet coats, allowing 10-15 minutes flash time between coats, depending on temperature and humidity.
4. Remove Masking: Remove the masking paper within 5 minutes after applying the final coat of primer to prevent hard paint edges.

Conclusion

Repairing rusted running boards yourself is a rewarding process that enhances your car’s appearance and protects it from further corrosion. By following these steps and using the right materials, you can effectively tackle rust and achieve a professional-quality repair. Remember, patience and attention to detail are key to success in auto body repair. With your running boards now restored and primed, they are ready for paint, completing the transformation and ensuring long-lasting protection against future rust.