There is a very simple formula to make a fab job of cleaning grout, it’s called pre wetting. If you soak the grout with water prior to cleaning when you come to add the SRP Xtreme Heavy Duty Tile & Grout High Alkaline cleaner diluted accordingly through the mono rotary water tank it will then do it’s job and sit on the surface where the dirt is. You then agitate with a soft to medium brush fitted, allow to dwell, agitate again and extract. The grout comes up immaculate each and every time. If it is really really bad, on the 2nd agitate phase sprinkle honing powder into the mix, this then cleans the surface mechanically by removing a few microns off the surface. So you have a chemical clean and a mechanical clean at the same time. I find it incredulous that so many people make the same mistakes over and over by either trying to clean grout when the floor is dry, without pre wetting, or they try to clean using a pad instead of a brush, then stand there, scratching their heads and blaming the cleaning product when the grout is still dirty. It’s because the the whole technique was wrong and the cleaning product they applied is now sitting at the bottom of the porous grout doing absolutely no good whatsoever. This is one of the first lessons we teach on our hard floor courses. Cleaning is a science that needs doing methodically, it’s not just about chucking some bleach down, battering it with water pressure and hoping for the best
