Body Filling, Panel Repair, and Dent Removal
What this domain tests
Dent repair, metal finishing, body filler selection and mixing, application, sanding, panel replacement, and corrosion protection.
Core rules
- Remove the cause of the dent where possible. Hammer and dolly to bring the metal close to shape before filler; filler is not a substitute for metal work.
- Use polyester body filler on clean, abraded steel or cured primer. Mix cream hardener at the ratio on the sheet, usually about 2%, and never guess by colour alone.
- Apply in thin passes. A thick blob traps air, shrinks, and cracks. Build only to the contour.
- Sand with 80 to shape and 180 to finish before primer. Use a block or board, not fingers, to avoid waves.
- Feather the filler edge into the surrounding paint; a ridge telegraphs through the topcoat.
- After welding or grinding, neutralise and prime bare metal immediately. Apply cavity wax or seam sealer where the original had it.
- Replace rather than repair a panel when damage is in a structural edge, a sharp crease, or an area that cannot be restored safely.
Worked example
A 150 mm dent in a steel door is filled with one thick application and sanded with 320 only. It later shows a ring and cracks. Reasoning: the thick filler shrinks and traps solvent; 320 does not shape the contour. Correct method: hammer and dolly, grind to bare steel, apply two or three thin filler passes, sand with 80 then 180 on a block, guide-coat, prime, and sand with 400 before base.
Traps
- Too much hardener makes filler brittle and fast-setting.
- Filler over rust or wax will lift.
- Sanding through the featheredge leaves a visible step.
- Skipping corrosion protection inside a repaired panel.