Here is what I know from the information I received from 5 independent firms who specialized in cleaning tile and the installation of it as well.
Two of the firms were owned by Italians, and three by Mexicans. I mention this because of their history/backgrounds of specialization. (Note: my family; cousins; etc were all Italians and did a lot of stone work as well. Very good at it too!)
Anyways, here is what all of them told us:
1. Pre-treat and or, use a rotary scrubber. This is called: mechanical action. The rotary brush wil clean the porous grout.
2. Follow with a light rinse using no more than 100-120 psi from a wet/dry wand with nozzles.
Reason, will not dislodge grout that lost its integrity, less likely to get water behind underneath the tile causing it to pop, etc......
They all mentioned that doing it this way you will see the cleanest clean you've ever seen without possible liability.
Something to think about???????
The JAGUAR MX-2 ETM @ cross-american.com