Sandpaper is one of the most indispensable tools in your workshop. Sandpaper is simply a piece of thick paper or material with an abrasive attached to its surface, but it has a variety of uses. The most common use for sandpaper is to smooth and shape a surface. You can also use sandpaper to roughen a smooth surface, prepare it to accept glue or paint, or remove a layer of paint or stain.
Sandpaper dates back to the thirteenth century in China and was made by attaching crushed glass, sand, seeds and shells to parchment. Throughout the years, the process and materials used have changed significantly. Modern sandpaper is not made of sand at all and is mass-produced in a factory.
The sandpaper begins as a long sheet of backing material wound on a roll. The backing runs through a machine that uses large rollers to print product information on one side and apply a heat setting adhesive to the other side. The backing is made of a wide variety of materials and thicknesses, depending on what the sandpaper will be used for. Sandpaper intended for palm sanders and sanding sheets is made of paper, and sanding belts and disks are made of fabric. Mylar and vulcanized fiber are used when a more firm backing is needed.
Once the backer paper is coated with adhesive, it continues, adhesive side down, to an area where the abrasive is added electrostatically. A worker pours abrasive material onto a conveyor belt that runs underneath the backer paper. An electrode and ground plate create an electrical field that gives the abrasive an electric charge opposite that of the backing. The abrasive is attracted to the backing and sticks to the adhesive side, creating an even coating. The most commonly used abrasives are aluminum oxide, garnet, silicon carbide and ceramic.
Sandpaper is made in different textures, or grit. The smaller the grit number, the coarser the sandpaper is. You can use different grits of sandpaper to achieve different finishes, from a rough, rustic appearance to a fine mirror finish.
The sandpaper then goes into an oven to set the glue. Once the glue is set, the sandpaper is coated with a resin to secure the abrasive to the paper. The sandpaper may go through additional treatments at this stage, such as adding a grinding aid or a material to reduce static electricity. Paper intended for fine finishes is passed between two steel rollers in order to crush any protruding abrasive. Peel-and-stick adhesive is also added during this stage.
Machines cut the sandpaper rolls into a variety of sizes to suit different needs. Sanding belts are made by cutting the sandpaper into strips and then stitching the ends together. Sandpaper sheets are made by cutting the roll into 8-by-11-inch rectangles. A large stamp cuts circular sanding disks out of the roll of sandpaper, complete with the center hole.