Deep Cleaning Porcelain Tile and Grout
We started by mixing a strong solution of Pro-Clean and NanoTech Ultra Clean and left to dwell for 10 minutes to allow the mixture to penetrate the build-up of ingrained dirt and grime. Then using a stiff grout brush we scrubbed each and every grout line to remove all traces of dirt and residue. Next we attached a stiff poly brush to our rotary machine and covered the whole floor making sure that we scrubbed each tile at least four times to make sure we removed as much dirt and grime as possible. We then rinsed the floor several times using clean water and removing slurry with wet vacuum making sure that all product had been removed.The tile and grout now look much cleaner and hopefully you can appreciate the difference in the photographs above.
Source: Porcelain Tile Maintenance Advice