How-To · · 6 min read
Understanding Abrasives: Grit, Bond and Backing Explained
Two discs with the same grit number can behave completely differently. To pick the right abrasive, you need all three variables: the grit, the bond that holds it, and the backing that carries it.
Grit: coarseness and material
Lower numbers cut faster and rougher: 40–60 for stock removal, 80–120 for shaping, 180–320 for finishing. Aluminum oxide is the general-purpose workhorse; zirconia lasts longer on steel; ceramic cuts coolest under heavy pressure; silicon carbide shines on stone, glass and paint.
Bond and backing
Resin bonds tolerate heat and pressure — that is what flap discs use. Paper backings suit sanders and fine finishes; cloth backings survive edges and corners; fiber discs need a backing pad and a firm hand.
- Grinding welds: zirconia or ceramic flap disc, 40–60 grit
- Prepping steel for paint: aluminum oxide, 80–120 grit
- Sanding wood finishes: paper-backed aluminum oxide, 180+ grit
- Rust on curved parts: silicon carbide, medium grit, light pressure
Pro tip: If the workpiece discolors, you are using too fine a grit or too much pressure — let the abrasive cut, not rub.