DIY Frequently Asked Questions / Sandpaper')">
Comes in five general types, including garnet, emery, aluminum oxide, silicon carbide and alumina zirconia. Of these, the first two are natural minerals or abrasives; the others are synthetic materials that are tougher and longer wearing than the natural abrasives.
All U.S.-manufactured sandpapers conform to the same numerical system for grading coarseness. The smaller the number, the coarser the grit.
Coarseness generally runs from 12 (extra coarse) to 1500 (ultra-fine). Grit finer than 600 is usually measured on the European FEPA scale, and identified with a “P” immediately before the number.
The back of each sandpaper sheet contains important labeling information, including product and lot number, abrasive type, grit size, whether it is open or closed coat and backing. The backing weight is rated by letter. “A” is the thinnest weight, while “C” and “D” are the best options for hand sanding of wood. “X” is effective for heavy-duty sanding.
Manufactured on a variety of backings, including paper, cloth and fiber.
Garnet is a reddish-brown natural abrasive. By special heat treatment, a tougher, sturdier grain is produced. Garnet is used almost exclusively in the woodworking field; it is not suitable for use on metal.
Emery is a black natural abrasive that can polish metal surfaces. Emery is typically used in conjunction with an oil lubricant.
Aluminum oxide is the most common general abrasive. It is a synthetic brown that is hard and long-wearing. It is used on wood, metal or painted surfaces and is well suited to finishing high-tensile materials such as steels and bronzes, as well as some hardwoods.
Silicon carbide is hard and sharp—effective in sanding low-tensile materials such as cast iron, aluminum, copper or plastic. It is also useful between coats of finish.
Alumina zirconia is harder than silicon carbide and tougher than aluminum oxide. It should be used for grinding and shaping metal and wood—not for polishing.
Sandpaper comes in two styles: open coat (OC) and closed coat. “Coat” refers to how densely the grain is adhered to the surface. “Closed coat” means 100 percent of the surface is covered with grain. Open-coat sandpaper has greater spacing between the grains, which prevents it from clogging up as quickly with sanding residue. Closed-coat sandpaper, however, fills more rapidly with the substance being sanded and must be discarded sooner.
Many styles available in sheets as well as sizes for various sanding power tools.