MATERIALS : To Smooth Things Over, Get Abrasive

Sandpaper is the common name for a variety of abrasive papers and cloth used on wood, plastics, plaster and metal. Sanding jobs vary from removal of old paint finishes and rust and rough shaping of wood stock to providing a final, silky-smooth surface.

Sandpaper is made of abrasive particles glued to paper backing. Abrasives are also affixed to emery cloth, which is stronger and more flexible than sandpaper. Particles are spaced close together (closed coat) for average work or spaced widely and evenly apart (open coat) for materials that tend to clog.

Coarse, open-coat grit is used for fast shaping of stock or removal of paint and rust while fine, closed-coat abrasives are used for soft substances--aluminum, plastics, resinous wood, plaster patches and paint between coats.

Abrasive papers are graded by number. The higher the number, the finer the grit: ultra fine (above 400), superfine (360 to 400), extra fine (280 to 320), very fine (160 to 240), fine (120 to 150), medium (80 to 100), coarse (50 to 60) or extra coarse (30 to 40). Some also come in “wet and dry” types, which can be used with water or oil for extra smooth finishes.

Use course or extra course grit to shape wood and remove heavy finishes, medium grit to smooth rough edges and cuts and to sand wood and plaster patches, fine or very fine grit to sand before finishing and extra, super or ultra fine grit to smooth undercoats and polish finishes. To avoid marring a finish, don’t use a grade coarser than necessary. Work in steps from coarse to finer grits.

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All abrasive papers and cloths come in pre-cut sizes or in sheets that can be folded and torn to size. Pre-cuts come in shapes designed to fit specific types of hand and power sanders, including disc-shaped ones to fit rotary sanders.

Common grit materials are flint, aluminum oxide, emery, garnet and silicon carbide.

* Flint is the least expensive abrasive, but it cuts slowly and dulls rapidly. It’s a good choice.

* Aluminum oxide is a tough, highly durable, synthetic material that’s an all-around paper for hand or power sanding on wood, metal or plastic. On wood use extra coarse or coarse for stripping and heavy sanding, medium for moderate sanding and fine for finish sanding. Use very fine after sealing or priming for varnish and paint. On plastics, use coarse for shaping, medium for light sanding and fine or very fine for finishing or scuffing. Aluminum oxide can also be used on metal: extra coarse or coarse for rust removal, coarse or medium for light sanding and medium or fine for removing burrs and for cleaning.

* Emery cloth is a fine, natural abrasive used on metal for stripping and rust removal (coarse), for removing burrs and cleaning (medium) and for finishing and polishing (fine). Because of its slow cutting action, it’s being replaced by other abrasives.

* Garnet paper is also durable and a natural grit. It’s used for heavy and moderate smoothing on hard and soft woods and for finish sanding and preparing wood for sealing and finishing.

* Silicon carbide is an extremely hard synthetic abrasive. It cuts fast and smooth and is used for wet or dry sanding. For varnishes and paint, use extra fine after sealing or priming and super fine between coats. For finishing or scuffing of plastics, very fine is best. Use medium for initial sanding and fine for finish sanding on plaster or wallboard.