Sandpaper is paper or cloth that has a coating of abrasives. There are a number of types and grits available.
Sandpaper also comes in wet and dry types and should be applied accordingly based on the purpose. Generally, dry sanding is used on metal and polyester body filler/putty. Wet sanding is used on primer- surfacer and topcoats.
Sandpaper is made for use with both sanding blocks and disc-type sanders.
The grit size of sandpaper is defined as (P) and sanding capability differs based on this value. The smaller the (P) value is, the larger the grit size and the stronger the sanding power.
Different Uses of Sandpapers
For Hand Sand
For Machine Sand
Usage
P16?P40
Separation of old paint film/Rough sanding for rust removal
P60?P80
P60?P80
Metal putty sanding
P80?P120
P80?P120
Polyester putty sanding
P320?P800
P320?P600
Primer-surfacer sanding
P1000?P1200
Contaminant removal before polishing with compound
P1200?P2000
Color sanding and clearcoat dust removal
Structure and Material
Abrasive material:
Aluminum oxide and silicon carbide are the main abrasive types used.
Aluminum oxide is brown or white and suitable for polishing the hard film surfaces with a high abrasive capability.
Silicon carbide is black. It is suitable for polishing soft film surfaces.
Backing
Sandpaper is abrasive grains are adhered to backing of paper, cloth, wet-or-dry paper, fiber, etc. The grit size, the thickness of the backing and grain material are usually indicated on the backing.
Grit Adhesive Methods:
There are two kinds of adhesives; open and closed coat.
Open coat is mainly used for dry sanding because the grit distance is far apart to resist clogging.
Closed coat is used for wet sanding because the grit is more densely distributed.
