I recently did both a carpet and a Tile & Grout cleaning job for a local Massage Envy franchise. On the lobby and bathroom tile, I sprayed down the cleaner, scrubbed with the Challenger T&G brush, went thru all the grout lines with my steam vapor machine, then padded up the whole mess. Customer called back the next day to report that the lobby looked OK but the light brown grout in the bathrooms still looked dingy. So I did a little online researching for highly praised grout cleaning products. I found many very strong reviews for ZEP Grout Cleaner & Whitener. I arranged to try it on a few grout lines in one of the Massage Envy bathrooms, as a test. It is AMAZING! It ate right thru the grimy top layer of the grout in just a minute or two, exposing the totally clean grout underneath. I highly recommend it.