You have to keep wiping it down with a clean sponge or cloth just like you would do if you were doing a counter top.

I sat down one time, with a chopstick no less...to clean one mosaic.
and wouldn't you know it...I was sitting in the front row of a courtroom, with a friend, for a driving infraction.
the judge stopped the proceeding, to let me know I needed to take it out of the room.
she considered that chopstick contraband and otherwise dangerous.
so, I left the room and continued to clean the piece, after grout..yes, film is a bit of a time consuming cleanup part of it.