Quick answer: Coated abrasives are abrasive grain bonded in a layer to a flexible backing – paper, cloth, film, fiber or foam. Sandpaper, sanding belts, discs, sheets and rolls are all coated abrasives. They differ from bonded abrasives (grinding wheels, where grain is molded into a solid block) and loose abrasives (polishing compounds and blasting media). What a coated abrasive does is set by four things: the grain (aluminum oxide, zirconia, ceramic or silicon carbide), the grit, the coat density (open or closed), and the backing.
What abrasives do
An abrasive is a hard mineral used with friction to remove material from a workpiece – to reshape it, or to give it a finish. Depending on the product you can grind, cut, sand, lap, polish or buff. Every grain has sharp edges; pressed against a softer material and moved, those edges cut tiny chips. Coarse grits cut big chips fast, fine grits cut small chips and leave a smoother surface, and more pressure or speed removes material faster – up to the point where heat and loading take over. Two habits get more out of any abrasive: replace it when it stops cutting instead of pressing harder, and run dust extraction (and coolant on metal) so it doesn't overheat and burn.
The three families of abrasives
| Family | What it is | Examples |
|---|---|---|
| Coated | Grain bonded in a layer to a flexible backing | Sandpaper, belts, discs, sheets, rolls, flap discs |
| Bonded | Grain molded with a bonding agent into a solid shape | Grinding wheels, cut-off wheels, sharpening stones |
| Loose / non-woven | Free grain, or grain in a nylon web or compound | Polishing compounds, blast media, scuff pads, buffing wheels |
This guide is about the first family, which is most of what we make. Our how sandpaper is made article covers the coating process itself.
Coated abrasive products
- Sanding belts – the fastest way to remove stock. Knife makers, metal fabricators, floor sanders and woodworkers run belts for grinding, shaping, stripping and sharpening.
- Sanding discs – for random orbital, DA and angle grinders. Surface prep, rust removal, paint stripping and finishing on larger flat surfaces.
- Sanding sheets – for hand sanding and pad sanders. Light stock removal, detail work, corners and edges.
- Sanding rolls – for drum sanders and for cutting your own strips. Mostly wood; also metal and plastic.
- Flap discs – overlapping flaps of coated abrasive on a grinder backing plate; grinding and blending in one.
Abrasive grains
| Grain | Color | Character | Best on |
|---|---|---|---|
| Aluminum oxide | Brown, or gold/white when coated | The most common grain. Tough, friable (self-sharpening), lowest cost. | Wood, general purpose, paint; closed coat for metal |
| Zirconia | Blue or green | Tougher than aluminum oxide, self-sharpening, long life at coarse grits. | Metal grinding, weld removal, heavy wood removal |
| Ceramic | Red/orange | Hardest and longest-lived; micro-fractures to stay sharp; cuts coolest under pressure. | Steel, stainless, hardened and exotic metals; knife making |
| Silicon carbide | Black | Sharpest and hardest but brittle, so it wears faster on steel. Cuts very cleanly. | Glass, stone, plastic, brass, wet sanding, between finish coats |
Aluminum oxide comes open coat (50–70% grain coverage) for stripping and finishing wood, and closed coat (near 100%) for removal and grinding on metal – see open vs. closed coat. Ceramic wants pressure and speed to work; run it light and it glazes. Zirconia is the value choice for metal grinding; ceramic is the performance choice. Compare them in aluminum oxide vs. zirconia and ceramic belts explained.
Backings
| Backing | Weights | Use |
|---|---|---|
| Paper | A, B (light) · C, D (medium) · E, F (heavy) | A/B: fine grits and hand sanding. C/D: general sanding, small power sanders. E/F: belts, rolls and heavy discs. |
| Cloth | J (flexible) · X (standard) · Y, YY (heavy) | Belts and grinding discs. J for contours and metal finishing; X for most belts; Y for coarse grits and high pressure. Polyester is water-resistant; cotton is more flexible. |
| Film | Polyester | Waterproof, very flat – wet sanding and precision finishing discs. |
| Fiber | Vulcanized fiber | Resin fiber discs for angle grinders. |
| Foam / sponge | – | Hand sanding contours and profiles. |
More on cloth weights in J-weight belts explained.
Grit sizes
The lower the number, the coarser the grit. A "P" prefix means the European FEPA scale, which lines up with the US CAMI scale at coarse grits and drifts apart above 220 – see US vs. European grading.
| Grit | Grade | Use |
|---|---|---|
| 24–60 | Coarse | Heavy stock removal, stripping paint and rust, shaping |
| 80–120 | Medium | Removing planer marks, leveling, general sanding, sharpening |
| 150–220 | Fine | Final sanding before finish, prep for paint |
| 240 and up | Very fine | Between coats, polishing, wet sanding, final edge on blades |
Our recommendations
| Application | Grain | Backing |
|---|---|---|
| Knife making | Ceramic for grinding; closed coat aluminum oxide or zirconia for profiling; J-weight for handles | X or Y cloth |
| Woodworking | Aluminum oxide – open coat on softwood, closed on hardwood | Cloth belts, paper discs |
| Metal fabrication | Ceramic or closed coat aluminum oxide; zirconia for value | X or Y cloth |
| Glass and stone | Silicon carbide | Cloth or film |
| Auto body and wet sanding | Silicon carbide | Latex paper or film |
Not sure? Tell us the material and the machine and we'll spec the abrasive. Browse sanding belts, discs and specialty abrasives, or read the abrasives dictionary for any term you don't recognize.
