Guide to Sandpaper and Abrasives

The Grit
Abrasive materials are essentially natural minerals or synthetic grains (called grits) that are glued to a backing. The effectiveness of the abrasive depends on the size, hardness and sharpness of each grit. Grits can be glued to a backing in tight-packed formation, which means the abrasive wears longer but clogs with waste faster. Grit peppered across the surface leaves space for waste to fall out but wears faster. Abrasives that can be used wet last much longer than those used for dry sanding.

Backing
Paper can be thin and flexible or stiff and robust, tear-resistant or waterproof. Paper-backed abrasive is used for hand-held electric sanders and hand sanding corks or blocks.
Cloth is expensive but more durable than paper. It’s used for hand-held belt sanders and huge belt-sanding machines.
Fibre backing is made with layers of paper bonded together with a special resin and for disc sanders.
Combination Backings are robust laminations of paper and cloth and used mainly for floor sanders.

Abrasive Type
These natural abrasives commonly found in hardware stores.
Sand/Quartz/Glass is hard enough for sanding timber, but doesn’t have very sharp edges.
Garnet is a mineral with sharp points, ideal for soft materials like timber. It breaks down quickly when used on hard materials.
Emery is a mix of corundum and magnetite and is good for rust removal, polishing, deburring and corrosion and paint removal. These synthetic grits give a superior sanding performance.
Aluminium Oxide is tough and the wedge-shape grit makes it suitable for smoothing and polishing steel, bronze, fibreglass, plaster, hard timbers and even stone.
Silcon CarbideE is the hardest and sharpest abrasive, and can be used wet or dry. Water or mineral turps reduces clogging and extends the life of the abrasive. It is used to sand primers, sealers, paints and non-ferrous metals, as well as for final finishing.
Aluminium Zirconia is tough and self-sharpens as it wears. It is used for heavy stock removal of metal and wood, and often found on sanding belts and flaps.

Sanding Rules
• Always sand along the grain of timber, not across.
• Don’t use worn-out coarse abrasive for fine sanding.
• Let the abrasive do the work – don’t apply excessive pressure.

Grits
40-60 Coarse
80-120 Medium
150-180 Fine
220-240 Very fine
280-320 Extra fine
360-600 Super fine
Begin a sanding job with alow grit abrasive, switching to higher grits progressively.

Shapes, Abrasives come in different shapes, sizes and grits for various applications. Click here to download PDF