The short answer
Window sill tracks collect everything the window keeps out — grit, pollen, dead insects, leaf fragments — and moisture turns it into a black paste that bakes into the corners. Cleaning a track means vacuuming the loose material first, then working the corners and weep holes by hand, wiping the channel, and leaving it dry so the sash glides again. Years of baked-in grime can leave a faint shadow even after a thorough clean.
Why tracks fill up
A window track is a horizontal channel at the bottom of a vertical opening — a perfect trap. Airborne grit and pollen settle into it, insects end up there, and any water that gets past the weatherstripping pools in the low corners. Mix that together over a few seasons and you get the dark, slightly greasy paste that's hard to shift.
It's worst on windows that are rarely opened, because nothing ever disturbs the build-up.
How a track is cleaned properly
Dry-vacuum the loose debris before anything gets wet — wetting it first just makes mud. Then the corners and the weep holes (the small drainage slots) are worked by hand with a detailing tool and cloth, the channel is wiped, and the track is left dry. The sash is opened and closed to confirm it glides.
Track detailing is usually added to a window visit rather than booked on its own.
Last reviewed September 2026. Written by the Aloe Cleaning team.