How to Sand a Run in the Primer Coat

Sandpaper is a vital tool for sanding and smoothing a vehicle's surface.

In the process of painting a car, primer is necessary to cover any bare metal, body filler or old paint before the paint is applied. The primer coat should be applied and smoothed before the paint is applied for the most flawless finish possible. When a run occurs in the primer, that run will show through the paint and cannot be repaired once the paint is sprayed. The only way to fix a run in the primer coat is to sand it smooth.

Things You'll Need

• Long sanding block
• 320-grit sandpaper
• 400-grit sandpaper
• Water

Instructions

1. Let the primer dry for 30 minutes after spraying it onto the vehicle. Leave the runs alone while the primer dries completely.

2. Sand the run in the primer coat using 320-grit sandpaper placed on a long sanding block. Keep the sanding block flat against the surface of the vehicle and sand evenly over the run. Keep the block horizontal and lead each stroke with the long edge of the block. Sand until the run is barely noticeable.

3. Replace the 320-grit sandpaper with 400-grit sandpaper. Sand the entire primer coat, frequently rinsing the surface of the vehicle and the sandpaper with water to keep the sanding buildup from scratching the surface. The 400-grit sandpaper smooths the primer coat, rids it of any remaining runs and gets it ready to be painted.