Tiles in public toilets and similar areas whether they be quarries or porcelain have one job…..which is to grip and be as non absorbent as possible. This means that naturally they grip dirt as well. All these areas, public toilets, changing rooms and gymnasium floors are therefore the most difficult to clean and moreover, to keep clean. The only way to clean them effectively is a mechanical clean coupled with an acidic or high alkaline chemical as well. If you use a low speed rotary machine fitted with a soft to medium brush, hot water (preferably) , high alkaline or acidic cleaner (test to see which works best) and finally honing powder the tiles and grout come up like new each and every time. However, the most important thing each and every time is to seal them afterwards to ensure ongoing cleaning is easier and the installation of a correct cleaning programme.
Kevin