Sanding a car for repainting is a meticulous process of removing the old, damaged clear coat and paint to create a perfectly smooth, clean surface for the new paint to adhere to. The core steps involve starting with a coarse grit sandpaper to strip the old finish, progressively moving to finer grits to eliminate scratches, and finishing with a "guide coat" to ensure a flawlessly level surface. Rushing this preparation is the most common reason for a poor paint job.
The first step is always a thorough wash and decontamination. Any dirt on the surface will be ground into the paint during sanding, causing deep scratches. After drying, use a grease and wax remover to eliminate any invisible residues that could prevent the new paint from bonding correctly.
Sanding Grit Progression is Key
You'll work through a sequence of sandpaper grits, either by hand for small areas or with a Dual Action (DA) sander for larger panels. The goal is to replace deeper scratches from a coarse grit with the finer, less visible scratches of the next grit.
| Sanding Stage | Grit Range | Primary Tool | Purpose | Key Consideration |
|---|
| Paint Stripping | 320 - 400 | DA Sander | Remove clear coat and level old paint | Avoid staying in one spot to prevent burning through the paint. |
| Scratch Removal | 500 - 600 | DA Sander/Block | Eliminate scratches from coarser grits | Sand until the surface has a uniform dull appearance. |
| Final Finishing | 800 - 1000 | Sanding Block | Create a fine scratch pattern for primer/paint | Use a guide coat (a light mist of contrasting aerosol) to reveal low spots. |
| Feather Edging | 320 - 400 | By Hand | Blend repaired areas into surrounding paint | Gently taper the edges of any bare metal or primer spots. |
After the final sanding with 800-1000 grit, the surface should feel smooth to the touch. A guide coat is crucial; when you lightly sand over it, any remaining low spots will still show the guide coat, indicating where more sanding is needed. Once the surface is perfectly level, blow off all dust with compressed air and wipe the entire car down with a dedicated wax and grease remover immediately before applying primer or sealer. Never skip this final cleaning step.
