sandpaper

(coated abrasives)

contents

grades

composition of the grit

density of the grit

adhesive

backing

formats and dimensions

sheets

rolls

discs

sleeves

belts

tapes

cords

Grades

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 defining a range of grain sizes, while CAMI defines the 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 detailed information.

In the abrasives industry, particle size is typically expressed in microns, the old term for the micrometer. But the CGPM, the controlling authority for SI, says microns should be called micrometers.

CAMI
Grade
FEPA
P-grade
Grit Description Average
particle
size in
microns
(inches)
Uses
      1842
(.07174)
 
  P12     1815  
  P16     1324  
16   4 very
coarse
1320
(.05148)
Removing rust, paint, etc.
  P20   1000
(.03838)
 
20   905
(.03530)
 
  P24   764
(.02886)
 
24   3 715
(.02789)
 
30   coarse 638
(.02488)
 
  P30   642
(.02426)
 
36   2 535
(.02087)
 
  P36   538
(.02044)
 
40   428
(.01669)
 
  P40   425
(.01601)
 
50   1 351
(.01369)
 
  P50   336
(.01271)
 
60   ½ medium 268
(.01045)
 
  P60   269
(.01014)
 
  P80   201
(.00768)
 
80   0 192
(.00749)
Coarsest grade needed in finishing surfaced lumber.
  P100   162
(.00608)
 
100   2/0 141
(.00550)
 
  P120   fine 125
(.00495)
 
120   3/0 116
(.00452)
 
  P150   100
(.00378)
 
150   4/0 93
(.00363)
 
180   5/0 78
(.00304)
Many workers feel 180 is as fine a grade as need be used on raw wood that is to be varnished or lacquered.
  P180     82  
220   6/0 very fine 66
(.00257)
 
  P220     68
(.00254)
 
Above are called "macrogrits"  Below are "microgrits".
  P240     58.5 ± 2.0
(.00230)
 
240   7/0 very fine 53.5
(.00209)
 
  P280     52.2 ± 2.0
(.00204)
 
  P320     46.2 ± 1.5
(.00180)
 
280   8/0 very fine 44
(.00172)
 
320   9/0 extra fine 36
(.00140)
Coarsest grade used to sand grain raised by stain.
  P400     35.0 ± 1.5
(.00137)
 
  P500     30.2 ± 1.5
(.00120)
 
360     extra fine 28.8
(.00112)
 
  P600     25.8 ± 1.0
(.00100
 
400   10/0 extra fine 23.6
(.00092)
Finest grit available in stearated paper.
  P800     21.8 ± 1.0
(.00085)
 
500     super fine 19.7
(.00077)
 
  P1000     18.3 ± 1.0
(.00071)
 
600     super fine 16.0
(.00062)
 
  P1200     15.3 ± 1.0
(.00060)
 
The remaining grades are used mainly in finishing metal and are most easily found at automotive supply stores.
  P1500     12.6 ± 1.0  
800       12.2
(.00048)
 
  P2000     10.3 ± 0.8  
1000       9.2
(.00036)
1000 to 1500 are used in rubbing out lacquer finishes on wood.
  P2500     8.4 ± 0.5  
1200       6.5
(.00026)
 
1500       3?  
2000       1?  

Composition of the grit

The abrasive may be any of the materials listed below.

flint garnet  
aluminum oxide silicon carbide  
alumina-zirconia emery  

Density of the grit

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.

Adhesive

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.

Backing

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.

Formats and dimensions

Sandpaper is available in a wide variety of forms:

Sheets

The standard sheet of sandpaper is 9 by 11 inches. Sanding appliances often call for a fraction of a sheet, and it is sometimes also sold as

Rolls

4.5

Discs

Diameters of 6", 8", 9", 10", 12", and 15".

Sleeves

These are cylinders that fit over rubber drums used, for example, on drill presses.

Belts

Some of the more common sizes are

Tape

In widths from 1/16 to 1/4 inch, with grades of 150 and 180 in aluminum oxide and silicon carbide. Crocus cloth is also available as tape.

Cord

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.

Standards

ISO

ISO 6344. Mastergrits

ANSI

B-74-12; B74-10. Washington Mills provides a detailed table from the ANSI standard:

www.washingtonmills.com/guides/grit-sizes-ansi/specification-b74-12-2011-table-2/

FEPA

FEPA-standard 43-1984 R 1993: Grit Sizes for Coated Abrasives; 32GB; 33GB

www.fepa-abrasives.org

www.washingtonmills.com/guides/grit-sizes-fepa/specification-fepa-42-12006-macrogrits/

www.washingtonmills.com/guides/grit-sizes-fepa/specification-fepa-42-22006-microgrits

JIS: R6001-87.

Resources

www.washingtonmills.com/guides/grit-sizes-ansi/particle-size-conversion-chart-ansi/

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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