Tip #5
Everything you need to know about Sanding! (continued)
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Where do you begin?

First, you need to familiarize yourself with the four most common types of abrasive materials available to the modern day woodworker: Flint, Garnet, Aluminum Oxide and Silicon Carbide.

FLINT is the least expensive - and least durable - of all abrasives. Made from crushed quartz, it's usually off-white in color. Because it's so inexpensive, it's best used for removing heavy layers of paint, wax or other finishes - or for sanding really resinous or “gummy” surfaces. When the abrasive “loads-up” with these clogging materials, just throw your sheet away and start with a fresh one. Since flint is really dull in comparison to other abrasives and has a tendency to leave flint dust embedded in the grain of the wood that can cause a chemical reaction with certain synthetic finishes, it is NOT recommended for any type of finish sanding.

ALUMINUM OXIDE is a synthetic abrasive, made from fusing bauxite in an electric furnace. It can be either red, brown, gray or black in color and offers very sharp grains that will out-wear Garnet abrasives. For this reason, it is the preferred abrasive for most machine sanding operations and is clearly the most readily available of all abrasive materials.

GARNET is an excellent natural abrasive that will leave an extremely smooth finish. For this reason, professional furniture and cabinetmakers prefer it for final, finish sanding operations. Although it is not a very “hard” material, it is probably the sharpest of all abrasives, with particles that have a tendency to fracture during use. This fracturing process is constantly exposing sharp, new edges... and that's why it cuts so smoothly. Garnet paper is almost always reddish in color.

SILICON CARBIDE is the hardest and most expensive of all abrasive papers. It is a synthetic product, made by heating silica and carbon to form a crystalline substance that is almost as hard as a diamond and very brittle.

It's usually only available in fine to ultra-fine grades. For that reason, it is not well suited for sanding unfinished woods and is best reserved for wet or dry finish sanding of paints, varnishes, urethanes and lacquers. Charcoal colored silicon carbide paper is used for both wet or dry sanding, while light grey colored papers are for dry sanding only.

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