Info.com discusses that sandpaper is a coated abrasive product that generally consists of flexible backing, a film of adhesive and a coating of abrasive grains. Different kinds of resins and hide glues are used as adhesives for sandpaper.
Most sandpaper products are made with silicon carbide or aluminum oxide, according to Info.com. Quartz grains are often used for wood polishing purposes. The grains are bonded using a strong glue. Additionally, heavy, flexible and strong paper is used.
Info.com states that the first recorded use of coated abrasive was in 13th century China. Natural gums were used to bind crushed seashells to parchment. In 1808, an article on coated abrasives mentioned that calcined, ground pumice was combined with varnish and applied on paper with a brush.
According to About.com, the first step in manufacturing a sandpaper product is printing the backer on the back of the paper. The grit and type of paper is noted on sheets of sandpaper. The grit, which comes from outside suppliers, is poured into a hopper. Different types of sandpaper use varying types of grit. Garnet and aluminum oxide are most commonly used in hand sandpapers. The next steps involve applying resin to the sandpaper, adding grit, drying the resin, adding a second coat of resin, flexing the sandpaper, applying the backing, printing the packaging and, finally, cutting and packaging.