thumb|upright=1.35|alt=Sheets of sandpaper with different grit sizes (40 (coarse), 80, 150, 240, 600 (fine))|Sheets of sandpaper with different grit sizes (40 (coarse), 80, 150, 240, 600 (fine))
Sandpaper, also known as coated abrasive or emery paper, is a type of material that consists of sheets of paper or cloth with an abrasive substance (grit) glued to one face.
There are many varieties of sandpaper, with variations in the paper or backing, the material used for the grit, grit size, and the bond. It is common to use the name of the abrasive when describing the paper, e.g. "aluminium oxide cloth" or "silicon carbide paper".
Sandpaper is produced in a range of grit sizes and is used to remove material from surfaces, whether to make them smoother (for example, in painting and wood finishing), to remove a layer of material (such as old paint), or sometimes to make the surface rougher (for example, as a preparation for gluing).
History
Since the ancient days, civilizations around the world used abrasive materials like fish scales or marble dust. The first recorded mention of a coated abrasive resembling modern-day sandpaper comes from 13th-century China, where crushed shells, seeds, and sand were bonded to parchment using natural gum. Modern coated abrasive technology developed throughout the industrial revolution, with inventors across the UK and USA refining the manufacturing process and trying new coating materials.
In addition to paper, the most often used backing materials for coated abrasives are cloth (natural or synthetic), PET film, and vulcanized fibre. Cloth is preferred for its high durability, and used in applications such as sanding belts.
Wet/dry sandpaper is more effective when used wet, because the water washes particles away from the grinding surface and reduces clogging.
Abrasive coating
The backing is coated in abrasive particles using an adhesive. Different parameters of the coating, such as the particle composition, size, or used adhesive can be changed to produce sandpaper suitable for different purposes.
Grit materials
Most sandpaper in the past used flint as the abrasive material. However, flint particles are too soft for most kinds of sanding, so flint paper is now barely used.
Several standards have been established for grit size, permissible tolerances and filtration method. The most prevalent standards are:
- The JIS grade, mostly used in Japan and other Asian countries.
- Micron grading, which specifies the exact size of particles in microns. Mostly used for extra fine grits (60-0.1μm).
Some sandpapers may only use descriptive nomenclature such as "coarse", "medium" and "fine", without referring to any standard. Those names are not regulated in any way and may differ between manufacturers.