There are several standards for coated abrasives, but by far the most commonly used are those of the Coated Abrasives Manufacturer's Institute (CAMI) and the Federation of European Producers of Abrasives (FEPA). Worldwide, the FEPA system is more common. The two systems are not strictly comparable, because FEPA defines a grade by specifying a range of grain sizes, while CAMI specifies an average particle size. For example, by the FEPA standard for macrogrits grade F180, no more than 3% by mass of the grit can have a particle size larger than 90 microns, and at least 94% must be larger than 53 microns. In F220 (a “microgrit”), no more than 3% can be larger than 75 microns, at least 50% must be in the range 50.0 to 56.0, and at least 94% must be larger than 45 microns. See the Standards section below for sources of detailed information.
In the abrasives industry, particle size is typically expressed in microns. But the CGPM, the controlling authority for SI, says microns should be called micrometers.
|Removing rust, paint, etc.|
|Coarsest grade needed in finishing surfaced lumber.|
|Many workers feel 180 is as fine a grade as need be used on raw wood that is to be varnished or lacquered.|
|Above are called “macrogrits” Below are “microgrits”.|
|P240||58.5 ± 2.0
|P280||52.2 ± 2.0
|P320||46.2 ± 1.5
|Coarsest grade used to sand grain raised by stain.|
|P400||35.0 ± 1.5
|P500||30.2 ± 1.5
|P600||25.8 ± 1.0
|Finest grit available in stearated paper.|
|P800||21.8 ± 1.0
|P1000||18.3 ± 1.0
|P1200||15.3 ± 1.0
|The remaining grades are used mainly in finishing metal and are most easily found at automotive supply stores.|
|P1500||12.6 ± 1.0|
|P2000||10.3 ± 0.8|
|1000 to 1500 are used in rubbing out lacquer finishes on wood.|
|P2500||8.4 ± 0.5|
The abrasive may be any of the materials listed below.
On closed-coat sandpaper, the grit covers 100% of the surface; on open-coat paper it covers 50% to 70% of the surface, the advantage being that the paper doesn't clog as easily. Wood is best sanded with open coat paper.
Some paper is treated with a soap-like substance to reduce clogging (“stearated” or “nonclog” sandpaper). Such paper is useful for sanding resinous woods and some finishes. Because it can leave a deposit, stearated paper should not be used if a water-based finish will be applied.
The grains of abrasive are held on the backing by glue, resin, or a combination of the two. The glue used in light duty papers is not waterproof.
An abrasive “paper” may be backed with either paper, cloth or a polyester film.
Paper backings are made in grades A through F, with F being heaviest. The A and B weights are used for finishing papers, C and D are general purpose weights, D and E are suitable for machine sanding, and F is used for belts.
Cloth backings are made in J, X, and Y weights, with Y the heaviest. The J weight is used when the sandpaper must conform to curved surfaces, and the Y weight is usually found only in heavy duty industrial applications.
Sandpaper is available in a wide variety of forms:
The standard sheet of sandpaper is 9 by 11 inches. Sanding appliances often call for a fraction of a sheet, and the fractional sizes are available.
Diameters of 6″, 8″, 9″, 10″, 12″, and 15″.
These are cylinders that fit over rubber drums used, for example, on drill presses.
Some of the more common sizes are
In widths from ¹⁄₁₆ to ¼ inch, with grades of 150 and 180 in aluminum oxide and silicon carbide. Crocus cloth is also available as tape.
The abrasive is coated on a round cord from 0.012 to 0.093 inch in diameter, in grades from 120 to 280, in the same materials as tape.
Foam blocks coated with abrasive are a popular substitute for a sanding block wrapped with sandpaper. Most are hand-sized, blocks 1 inch thick, 4½ inches long, and around 2¾ to 3¾ inches thick. Many other sizes and shapes are made. Those with sharp angles are particularly useful. The better ones are claimed to last 5 times longer than sandpaper, and are water-washable.
Sanding blocks are also made in which the abrasive, instead of being a coating on the block's surface, is incorporated throughout the block.
oscillating introduced by Fein and now available fr described as 3 by 3
ISO 6344. Mastergrits
B74-10. ANSI B74.12-2018
Washington Mills provides a detailed table based on ANSI standards:
FEPA-standard 43-1984 R 1993: Grit Sizes for Coated Abrasives; 32GB; 33GB.
The Unified Abrasives Manufacturers Association (www.uama.org) offers four lessons on abrasives. Abrasives 101 goes into some detail. The other three are sets of PowerPoint slides, unfortunately with minimal explanations.
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Last revised: 16 May 2019.