After I finished grinding a marble floor with a 120 grit I noticed that the is grout missing. Can I replace the missing grout without removing all the grout? How do I match the color of the existing grout?

Yes, you can replace the missing grout. Be sure to use only unsanded grout . You will also need to wait 24 hours before proceeding with honing or you can wait until you have polished the floor and then replace the grout. Matching the color of the existing grout can prove difficult since grout color will fade over time. The best way is to obtain grout samples from your local tile store and bring them to the job and compare the samples with the grout.

TIP To match the grout it may be necessary to color all the grout. If you choose this option, allow the grout to cure for at least 24 hours.