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Abrasive Types / Materials

Abrasives come in many different materials and each has its own merits and uses for particular types of sanding. Choosing the right type to use for a project can be confusing. But, with a little understanding of the properties of each one, you can at least make an informed decision.

Some properties to consider when looking for deciding on a sandpaper to use are:

  • Friability - means that the grains in sandpaper break down to expose fresh cutting edges as the sandpaper wears. Fresh cutting edges help the sandpaper to stay sharp and cut through more material longer.
  • Grit - Grit refers to the size of the particles of abrasive material on the medium. Coarser grit material is used to take off more material faster while finer grits are used to smooth out the finished piece.
  • Open- and Closed-Coat:
    • Open-Coat - Most sandpaper for woodworking has an Open-Coat, meaning that abrasive grains cover only 40-70% of the backing material. The space between the grains give sawdust a place to go so the paper doesn't clog. open-Coat is better when less aggressive sanding is needed. It lasts longer than closed-coat sandpaper. Open-Coat sandpaper is good for sanding resinous softwoods such as white and yellow pine, and soft materials such as primer and topcoat paints.
    • Closed-Coat - Abrasive grains cover 95-100% of the surface of the backing. Closed-Coat produces a more uniform scratch pattern but clogs more quickly than Open-Coat. It's a good good choice when sanding finishes and for sanding hardwoods such as Oak or Maple. It provides more aggressive sanding and removes material quicker than Open-Coat.
  • Backing Material:
    • Cloth - Cloth backing is used on sanding discs and belts. Cloth is the stiffest and least flat backing material for abrasives. It will produce the coarsest and fastest cut. Cloth comes in two grades: J which is light and X which is heavy and less flexible. Cloth comes in varying degrees of these two grades as JF, J, XF, X, YX, and YY. JF through X are the lighter and more flexible of all the grades.
    • Paper - Paper backing is not as stiff as cloth backing but is flatter. It comes in grades A, C, D, E and F with A being the lightest and most flexible and F being the heaviest and strongest. Paper backing is generally used on sheet abrasives. The stiffer the paper, the less abrasive materials will deflect while cutting. They will cut deeper and faster. Softer backings will allow the abrasives to deflect more, giving light scratches and a smooth finish.
    • Film - Polyester film, including Mylar, look and feel like plastic. They are extremely flat, durable, and pretty stiff. Film backing is very smooth and even as opposed to paper backing which is made up of fibers and is irregular. Film backing abrasives give the most consistently even cut and at a faster rate than paper backed abrasives.

Material Form Price Grain Shape Friability Durability Suggested Use Formats Comments
Ceramic; Alumina Zirconia Manufactured, Synthetic $$$ Variety of shapes from blocks to heavy wedges to flake-like shards. More uniform in structure than AO or ZO. Not friable Better durability than AO. Extremely tough, sharp, and long-wearing. Very aggressive. Best for fast removal of material in woodworking. Best choice for hogging off stock, roughing out shapes, removing finish, and leveling uneven boards. Generally, available in coarse-grit cloth belts and discs. They are not friable and do not renew their cutting edges when sanding wood. Doesn't dull quickly. Alumina Zirconia, a tough alloy of Aluminum Oxide and Zirconium Oxide is actually a ceramic abrasive.
Aluminum Oxide (AO) Manufactured, Synthetic $ Blocky Friable Exceedingly durable with good shelf life. Works well for bare wood, painted surfaces, and metal. Can be paired with Silicon Carbide on woodworking projects. Found more often in Coarse grits. Most frequently used grain in the industry. Most economical. One of the best general purpose abrasives in woodworking.
Available in different grades:
  • White: Most pure, toughest, and hard wearing. Cuts well in metal working applications.
  • Pink: A good general purpose AO used in premium woodworking projects.
  • Brown: A little softer and works well in hand held applications.
Silicon Carbide (SC) Manufactured, Synthetic $ Needle-like grains that resemble shards of broken glass Very friable Less durable because it is brittle and has a more narrow shape that wears down at an increased rate. Very forgiving. SC is too friable for bare-wood sanding but, the friability makes it excellent for finer sanding. Can be paired with Aluminum Oxide on woodworking projects. Good for paint removal. Excellent for smoothing a finish between coats and for rubbing out film finishes like lacquer and shellac. Better than AO for cutting hard materials such as finishes, paint, plastic, glass, fiberglass, and metal. Most commonly found in Fine grits rather than coarse. Cuts quickly and produces a uniform scratch pattern. Almost always on waterproof paper. Can be washed and reused.
Garnet Natural $$ Blocky in shape Not Friable Dulls very quickly but it tends to create a smoother surface on wood than AO of the same grit. Produces the smoothest finish of all abrasives. Well-suited for final sanding of wood surfaces. Softness causes it not to leave pigtail-like scratches as AO will do. Pigmented stain prefers a garnet-sanded surface. Final sanding. The only natural material still widely used in woodworking.
Flint Natural $ Not very durable. Limited cutting ability. Sandpaper Classic tan sandpaper.
Zirconia (ZO), Zirconium Oxide Manufactured, Synthetic $$$ Very, very hard. A step or two away from Diamond. Tougher than pink and brown AO. Ideally suited for grinding very hard and dry woods because of the extremely abrasive-resistant ZO grit. Well-suited to high pressure machining and grinding. Best for grinding and finishing of steel. Zirconium is synthetic diamond. Struggles to effectively grind mill scale in metal work.
Cerium Oxide (CO) Manufactured, Synthetic $$$ Best material for very fine polishing and for polishing glass.
Trizact (from 3M) Manufactured, Synthetic $$$$ Precisely shaped pyramids of micron grade mineral Friable Because it is friable, disc life is extended up to 10 times longer than regular sandpaper. Use for precision polishing, detailing, and finishing. Used in automotive industry to polish fine scratches from auto clear coats. Discs Use when high gloss level is required. Use wet to achieve desired finishes.

Aluminum Oxide (AO) and Silicon Carbide (SC) are the two most widely used forms of sandpaper across the woodworking industry due to their versatility, affordability, and consistent performance.

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