TYPES OF SANDPAPER

There are countless varieties of sandpaper, with variations in the paper or backing, the material used for the grit, grit size, and the bond.

In addition to paper, backing for sandpaper includes cloth (cotton, polyester, rayon), PET film, and "Fiber". Cloth backing is used for sanding discs and belts, while Mylar is used with extremely fine grits. Fiber or vulcanized fiber is a strong backing material consisting of many layers of impregnated paper made from rags. The weight of the backing is usually designated by a letter. For paper, the letters range from A to F, with A being the lightest and F the heaviest. Letter nomenclature is different for cloth, with the weight of the backing being, from lightest to heaviest: J, X, Y , T and M.

Materials used for the abrading particles are:

As well, 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.

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

Sandpapers can also be open coat, where the particles are separated from each other and the sandpaper is more flexible. This helps prevent clogging of the sandpaper. The wet and dry sandpaper is best used when wet and when using material like acrylic where it leaves a nice smooth feel afterwards.

Sandpaper comes in a number of different shapes and sizes.

Grit size refers to the size of the particles of abrading materials embedded in the sandpaper. A number of different 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 Manufacturers' 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 Japan Industrial Standards Committee (JIS), the micron grade (generally used for very fine grits). The "ought" system was used in the past in the United States. Also, cheaper sandpapers sometimes are sold with nomenclature such as "Coarse", "Medium" and "Fine", but it is not clear what standards these names refer to.

The following table compares the CAMI and "P" designations with the average grit size in micrometers (µm).

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