Why grout goes gray and whether sealing is worth it

Cement grout is porous. It absorbs whatever touches it: dirty mop water, cooking grease, pet accidents, the winter grit tracked into the entry. A mop moves dirt from the tile into the grout line and leaves it there, which is why the tile looks fine and the grout gets darker every year.

Cleaning grout properly means an alkaline cleaner to loosen the soil, agitation with a grout brush, and a pressurized rinse that flushes the dirty water out of the pore and captures it rather than spreading it. The turbo tool we use does this under a contained head so nothing sprays onto cabinets.

Sealing

A penetrating sealer soaks into the grout and fills the pores so water and soil sit on the surface instead of absorbing. Sealed grout still needs mopping, but the mop actually removes the dirt instead of pushing it in. Sealer lasts two to three years in a busy kitchen or entry and longer in a bathroom.

Is it worth it?

If you have just had grout cleaned and it looks new again, sealing is what keeps it that way. If grout has never been sealed since installation, it has been absorbing for years and the cleaning-plus-sealing combination is the reset. It costs a fraction of regrouting.