Far longer than most people allow, if extraction keeps it clear — a disc is finished when it stops cutting, not when it looks dirty, and most are thrown away clogged rather than worn out.
Most sanding discs are binned with plenty of abrasive left on them, because they stopped cutting rather than wore out. Those are different failures with different fixes.
Clogging
Dust, resin or finish packs the spaces between the grains. The disc goes shiny and dark, stops removing material, and starts generating heat instead. This accounts for the majority of discarded discs, and working extraction is what prevents it.
Wear
The grains fracture and round over. The disc still looks reasonable and simply cuts more slowly and more finely than the number on the back suggests.
Telling them apart
Glazed and dark means it clogged. Even and pale, but the sander is taking twice as long, means it is worn.
Getting more out of them
Extraction first and always. A disc on a sander with a blocked hose lasts a fraction as long as the same disc with air moving through it.
Then: less pressure, mesh abrasive on resinous timber, and a crepe rubber cleaning stick, which recovers a clogged disc surprisingly well.
What a tired disc costs you
A worn 120 behaves like a 180 and leaves the surface under-prepared for the grit you think you used. That is the scratch pattern that appears after the first coat.
Last reviewed 2026-08-12