Cement grout is porous, and it goes grey for three different reasons.
Diagnose first
Scratch a hidden joint gently with a fingernail. If a lighter color appears immediately, the dirt is on the surface and it will clean. If the grey goes right through, it is stained. If the joint is visibly lower than the tile, it has eroded.
Surface dirt: steam and a nylon brush
A detail nozzle with a small round brush, worked along the joint slowly, wiped immediately with a cloth. This is the single job steam machines are best at.
Stained through: colourant or replacement
Grout colourant seals and recolours the joint. It is a real solution and it is a coating, so it needs the joint clean and dry first. The alternative is raking out and regrouting.
Eroded: regrout
No cleaning method adds material back.
Then seal it
An impregnating grout sealer on clean dry joints is what stops the next round. It costs very little and it is the step almost everyone skips.
The questions we hear
Will steam make grout white again?
It will remove everything sitting in the pores, which on a kitchen floor is most of the discolouration. It will not touch dye that has penetrated, and it will not replace grout that has worn below the tile edge.
Is a rotary nozzle or a wire brush a good idea?
No. Both remove grout as well as dirt, and once the joint is below the tile surface it collects dirt faster and cannot be cleaned at all. Nylon brushes and heat only.
Last reviewed 2026-08-16
