Step-by-Step Auto Sanding

Sand old paint and primer off of a car using a dual-action sander and 80-grit sandpaper. This can be used to sand the car down to the bare metal without digging into the metal surface. A dual-action sander oscillates in a way that sands the surface without gouging the metal. Hand sanding at this stage is possible, but it won't come out as smooth and can take hours rather than the 30 minutes it takes to sand a car with the sander.

Use 120-grit sandpaper to sand down any body filler used on the car's surface. Place the sandpaper on a sanding block. Keep the block horizontal and move it at an angle to make X shaped patterns while sanding. Always lead each stroke with the long edges of the block, not the short ends. Using the short ends and moving the block left and right can cause a ditch in the filler that may not be noticed until the final paint has dried.

Cover the sanding block in 220-grit sandpaper to sand the primer coat after it has dried. Use the same techniques as when sanding with the previous grit. The primer should be gently sanded to only knock down the very top layer. Sanding too much can make the metal show through and make a low spot in the primer.

Go over the entire car using 380-grit sandpaper to get the smoothest finish before applying the paint. This can be done using your hand or a sanding block. Be careful to only sand gently and never sand the edges or corners of the car for more than a second or two. Sandpaper can easily dig too deep on the edges and cause the underlying layers to show through.