Sandpaper

Most do-it-yourselfers still refer to various grades of "sandpaper," but the proper term for these sanding sheets is "coated abrasives." There are four factors to consider when selecting any coated abrasive: the abrasive mineral, or which type of rough material; the grade, or the coarseness or fineness of the mineral; the backing (paper or cloth); and the coating, or the nature and extent of the mineral on the surface.

Sandpaper can be held in the hand or wrapped around a sanding block.

Paper backing for coated abrasives comes in four weights: A, C, D, and E. A (also referred to as "Finishing") is the lightest weight and is designed for light sanding work. C and D (also called "Cabinet") are for heavier work, while E is for the toughest jobs. The coating can be either open or closed. Open coated means the grains are spaced to only cover a portion of the surface. An open-coated abrasive is best used on gummy or soft woods, soft metals, or on painted surfaces. Closed coated means the abrasive covers the entire area. They provide maximum cutting, but they also clog faster and are best used on hard woods and metals.

There are three popular ways to grade coated abrasives. Simplified markings (coarse, medium, fine, very fine, etc.) provide a general description of the grade. The grit refers to the number of mineral grains that, when set end to end, equal 1 inch. The commonly used O symbols are more or less arbitrary. The coarsest grading under this system is 41/2, and the finest is 10/0, or 0000000000.

The following chart contains information on sandpaper types and uses.

SELECTING SANDPAPER

Grit	Number	Grade	Coating	Common Uses
Very coarse	30 36	21/2 2	F,G,S F,G,S	Rust removal on rough-finished metal.
Coarse	40 50 60	11/2 1 1/2	F,G,S F,G,S F,G,A,S	Rough sanding of wood; paint removal.
Medium	80 100 120	0(1/0) 00(2/0) 3/0	F,G,A,S F,G,A,S F,G,A,S	General wood sanding; plaster smoothing; preliminary smoothing of previously painted surface.
Fine	150 180	4/0 5/0	F,G,A,S F,G,A,S	Final sanding of bare wood or previously painting surface.
Very fine	220 240 280	6/0 7/0 8/0	F,G,A,S FAS FAS	Light sanding between finish coats; dry sanding.
Extra fine	320 360 600	9/0 _2 _2	FAS S S	High finish on lacquer, varnish, or shellac; wet sanding. High-satinized finishes; wet sanding.

1 F = flint; G = garnet; A = aluminum oxide; S = silicon carbide. Silicon carbide is used dry or wet, with water or oil.
2 No grade designation.

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