Steve -
We just got back this afternoon from doing that type of job. Customer said, and I quote, "Wow".
So, yes, it can be cleaned. But maybe not as easily as a quick mopping.
First, to avoid the job yourself, ask if anyone on this forum is near you.
http://www.network54.com/Forum/279673
They mostly know how to do this stuff. Much easier to just hire them and pay their oversized fees...or....
If you wants to do it yerself, ....
1. Protect surrounding surfaces with tape and plastic (blue first, then duct tape on top)
2. Vacuum to remove grit
3. Soak floor with heavy duty alkaline (degreasers) at high concentration.
4. Allow 5-10 minutes dwell time
5. Scrub with nylon brushes - rent rotary floor machine with stiff brushes, preferably. DON'T UNDERESTIMATE HOW INCREDIBLY SLIPPERY HIGH ALKALINES ARE OR YOU WILL KILL YERSELF GOOD.
6. IMMEDIATELY BEFORE THE MUCKY STUFF DRIES...WET VACUUM IT UP WITH HIGH QUALITY WETVAC, THE KIND YOU RENT, NOT THE CHEAP KIND HOMER SELLS THAT DUZZN'T WORK.
7. Before it dries, rinse well
8. Repeat if you didn't get all of it. Hand scrub edges and corners which will have mysteriously multiplied while you weren't looking.
9. Then repeat with different mophead and new water and acid solution. Can use sulfamic, or Viper Renew (made by Bridgepoint??), mine personal favorite, only after testing to see if it's too strong. Repeat the scrubbing and wet vaccing. Don't let the acid touch anything, especially marble or chrome and finished metal like brass.
10. Allow to dry or speed it up with air movers.
11. Analyze if the grout has cleaned uniformly or spotty and blotchy...(half the time)
12. If uniform, you're done cleaning and now just put some clear sealer on and wipe it dry and go bragging
13. If blotchy, select a grout color from any one of 4 major manufacturer's grout color chart, closer the better, and then order a grout stain/dye/color sealer that matches, wait til it arrives, use application instructions and prepare to be amazed that their product has made your floor appear to be a new install.
14. Act like you never had a doubt all along.
