The month-later problem Cleaned grout that goes dark again in 30 days
Plenty of homeowners have paid for tile cleaning, loved the result, and then watched the grout darken back down within a month. The reason is simple. Cleaning opens the grout pores back up, and if nothing seals them, the next round of mop water and foot soil sinks right back in. The floor is now cleaner and more absorbent at the same time.
We finish with a penetrating grout sealer when the grout is in good shape and the homeowner wants the results to last. The sealer bonds inside the cement instead of laying on top, so water beads, soil sits on the surface where a mop can grab it, and the lines stay closer to their original color between cleanings.
If the grout is cracked, missing in spots, or crumbling under a fingernail, sealing is not the right call and we will say so. On stone floors that have gone dull, stone honing for dull floors or stone sealing for lasting protection may be the better follow-up than another cleaning pass.