If you are a do-it-yourself type, you have had the occasion to use sandpaper. Have you ever given thought to what is actually on that sandpaper? It's not just sand glued on paper. There are four different types of minerals that make up the various grits of sandpaper. The finish you hope to achieve or the job at hand will determine which paper to choose for the results you want.
The Grades of Grit
Your sandpaper is graded according to the amount of abrasive particles (grit) per square inch. The six abrasive categories range from course to super fine and between them include medium, fine, very fine and extra fine. Your choices will depend on the finish you hope to achieve. These particles or categories consist of one of four minerals that make up sandpaper: aluminum oxide, garnet, ceramic (alumina zirconia) and silicon carbide.
If your sandpaper is brown in color, it is made up of aluminum oxide. This is the most common sandpaper used in woodworking. Its versatility allows it be used on both bare and painted wood. Popular because of its sturdy nature, it has a longer use life than either garnet or silicon carbide sandpapers. Because of its toughness it is also the choice for power sanders and sanding metal. Premium-grade sandpapers are often aluminum oxide.
When your sandpaper has a distinctive reddish brown to orange hue its mineral base is garnet. It does not last as long as aluminum oxide sandpaper. On the plus side, your garnet sandpaper gives a much smoother finish. This is the type of sandpaper you want to use when you intend to stain a piece of wood. Garnet sandpaper tends to burnish (close the pores) of the wood pieces allowing for a more even stain application.
Also known as alumina zirconia, this sandpaper is long wearing with a tough sharp grit. It leaves a rough finish and must be used with caution as it can easily sand away more than you intended. An expensive grit to use, it is often blended with other abrasives. When using a sander, either belts or disks, you are likely using a sandpaper with a ceramic grit. Sander belts are blue, while sanding paper is brown.
Known for its ability to be used for either wet or dry sanding, it unfortunately wears out quickly. You would usually use it for sanding between coats of paint and on metal finishes. The form used for wet sanding is black in color, though it can also be used for dry sanding. You can also find it in a gray color. Unlike aluminum oxide, there is only one grade of silicon carbide sandpaper.