I'm frustrated....how can I get some oldish travertine tiles in a shower really clean? and the grout? We bought a vacation condo and these tiles are probably about 10 years old and really need a good cleaning. Can anyone give me some tips that will really get the tiles AND the grout clean and not hurt the tiles? And the best way to keep it up once clean? I have been using the Finazzle products, but they are not working. Would appreicate any help in this. Thanks so much.