Sanding a vehicle before painting is very important. In fact, professional painters often state that the sanding process is far more important than the actual painting process. Sanding too much or too little can cause imperfections on the surface of the car. These imperfections are almost always seen after the paint has been sprayed and dried. The only way to correct these imperfections is to sand the paint away and start over.
Sandpaper Grit
The grit of the sandpaper you use is one of the most important things to get right when sanding a car. A rough 80-grit paper is used to sand paint and primer away and reveal bare metal. This same sandpaper also causes small scratches in the surface of the metal. A lighter sandpaper, such as 150- or 300-grit, must then be used to remove those scratches but can cause even smaller scratches. The higher the grade of sandpaper, the finer it is, meaning fewer or no scratches.
Sanding Blocks
The long, flat sanding block is the most important tool in a complete paint job. The long sanding block is about a foot long and is used with sandpaper to cover the flat side of it. The sanding block is held with two hands and is slowly and evenly used to sand the flat surfaces of a vehicle. When used like this, the sanding block lightly sands the top layers of paint or primer on the car, revealing any low or high spots on the surface. These areas can then be repaired and made flush with the car's surface.
Wet Sanding
Wet sanding is done right before painting and again after the entire paint job has been finished and dried. Very fine sandpaper of 300-grit or higher is used for wet sanding. The sandpaper is kept soaking wet through the entire sanding process so that the debris is not rubbed into the surface of the car. Wet sanding before painting smooths the primer with no sandpaper scratches. Wet sanding after a paint job actually smooths down the clear coat of the paint to remove any slight imperfections. The clear coat will look dull, but then it is buffed and looks brilliant.
