Sandpaper

The first recorded instance of sandpaper was in 13th-century China when crushed shells, seeds, and sand were bonded to parchment using natural gum.[1] In the Bible, King Solomon is mentioned to have used a mysterious abrasive called shamir allowing the king to build his temple (e.g. cut huge blocks of stone) without using iron tools, since the temple was meant to be a place of peace and iron was used in war. Shamir was also held in Hebrew lore as being a magical worm capable of cracking glass when resting on it.[2][3]

Shark skin (placoid scales) has also been used as an abrasive and the rough scales of the living fossil, Coelacanth are used for the same purpose by the natives of Comoros.[4] Boiled and dried, the rough horsetail plant is used in Japan as a traditional polishing material, finer than sandpaper.

Glass paper was manufactured in London in 1833 by John Oakey, whose company had developed new adhesive techniques and processes, enabling mass production. Glass frit has sharp-edged particles and cuts well whereas sand grains are smoothed down and do not work well as an abrasive. Cheap sandpaper was often passed off as glass paper; Stalker and Parker cautioned against it in A Treatise of Japaning and Varnishing published in 1688.[5]

In 1921, 3M invented a sandpaper with silicon carbide grit and a waterproof adhesive and backing, known as Wet and dry. This allowed use with water, which would serve as a lubricant to carry away particles that would otherwise clog the grit. Its first application was in automotive paint refinishing.[6]

320 grit silicon carbide sandpaper, with close-up view

In addition to paper, backing for sandpaper includes cloth (cotton, polyester, rayon), PET film, "fibre", and rubber. Cloth backing is used for sandpaper discs and belts, while mylar is used as backing for extremely fine grits. Fibre or vulcanized fibre is a strong backing material consisting of many layers of polymer impregnated paper. The weight of the backing is usually designated by a letter. For paper backings, the weight ratings range from "A" to "F", with A designating the lightest and F the heaviest. Letter nomenclature follows a different system for cloth backings, with the weight of the backing rated J, X, Y, T, and M, from lightest to heaviest. A flexible backing allows sandpaper to follow irregular contours of a workpiece; relatively inflexible backing is optimal for regular rounded or flat surfaces. Sandpaper backings may be glued to the paper or form a separate support structure for moving sandpaper, such as used in sanding belts and discs. Stronger paper or backing increases the ease of sanding wood. The harder the backing material, the faster the sanding, the faster the wear of the paper and the rougher the sanded surface.

Types of abrasive materials include:

• Glass: No longer commonly used.
• Flint: No longer commonly used.
• Garnet: Commonly used in woodworking.
• Emery: Commonly used to abrade or polish metals.
• Aluminium oxide: The most common in modern use, with the widest variety of grits, lowest unit cost; can be used on metal (i.e. body shops) or wood.
• Silicon carbide: Available in very coarse grits all the way through to microgrits, common in wet applications.
• Alumina-zirconia: (An aluminium oxide–zirconium oxide alloy), used for machine grinding applications.
• Chromium(III) oxide: Used in extremely fine micron grit (micrometre level) papers.
• Diamond: Used for finishing and polishing hard metals, ceramics and glass.
• Ceramic aluminum oxide: Used in high pressure applications, used in both coated abrasives, as well as in bonded abrasives.

Sandpaper may be "stearated" where a dry lubricant is loaded to the abrasive. Stearated papers are useful in sanding coats of finish and paint as the stearate "soap" prevents clogging and increases the useful life of the sandpaper.

The harder the grit material, the easier the sanding of harder surfaces like hardwoods such as hickory, pecan, or wenge. The grit material for polishing granite must be harder than granite.

Different adhesives are used to bond the abrasive to the paper. Hide glue is still used, but this glue often cannot withstand the heat generated during machine sanding and is not waterproof. Waterproof sandpapers or wet/dry sandpapers use a resin bond and a waterproof backing.

Sandpaper can be either closed coat or open coat.[7] Approximately 90% to 95% of the surface is covered with abrasive grains with a closed coat. Closed coat sandpaper is good for hand sanding or working with harder materials. In comparison, 50% to 70% of the surface is covered with abrasive grains with open coat sandpaper. The separation between particles makes the sandpaper more flexible, which prevents the sandpaper from clogging. However, the gaps in grit coverage limits the sandpaper's ability to perform even polishing jobs. Open coat sandpaper is better for softer materials.

Wet and dry sandpaper is more effective used wet because clogging is reduced by particles washing away from the grinding surface.[8]

Sandpaper comes in a number of different shapes and sizes:

• sheet: usually 9 by 11 inches (23 by 28 cm), but other sizes may be available
• belt: usually cloth backed, comes in different sizes to fit different belt sanders.
• disk: made to fit different models of disc and random orbit sanders. May be perforated for some models of sanders. Attachment includes pressure-sensitive adhesive (PSA) and "hook-and-loop" (similar to Velcro).
• rolls: known as "shag rolls" by many contractors
• sponge: for tight places

Grit size refers to the size of the particles of abrading materials embedded in the sandpaper. These measurements are determined by the amount of the abrasive material that can fit through a square inch filter.[9] Several standards have been established for grit size. These standards establish not only the average grit size, but also the allowable variation from the average. The two most common are the United States CAMI (Coated Abrasive Manufacturers Institute, now part of the Unified Abrasives Manufacturer's Association) and the European FEPA (Federation of European Producers of Abrasives) "P" grade. The FEPA system is the same as the ISO 6344 standard. Other systems used in sandpaper include the Japanese Industrial Standards Committee (JIS), the micron grade (generally used for very fine grits). Cheaper sandpapers may sometimes only use descriptive nomenclature such as "coarse", "medium" and "fine" without referring to any standard.

The following table, compiled from the references at the bottom, compares the CAMI and "P" designations with the average grit size in micrometres (µm).

Sandpaper tends to be a generic term for several simiar abrasive papers and cloths

• Belt sander
• Emery (mineral)
• Grain size
• Grind
• Grinding machine
• Polishing
• Rotary tool
• Sander
• Sanding block
• Sanding sealer

• Michael Dresdner (1992). The Woodfinishing Book. Taunton Press. ISBN 1-56158-037-6
• Bob Flexner (2005). "Understanding Wood Finishing — How to Select and Apply the Right Finish". Fox Chapel Publishing. ISBN Hardcover:978-1-56523-548-9. ISBN Paperback:978-1-56523-566-3

Wikimedia Commons has media related to Sandpaper.

• Federation of European Producers of Abrasives
• sizes.com on sandpaper
• Conversion Chart Abrasives - Grit Sizes