QMT Stoneclean is an acidic cleaner (very acidic) even when diluted with water it reads 2 on the ph scale you really have to be careful with these types of cleaners, how badly soiled are the tiles, I would recommend to try a small area with a damp microcleaaning pad impregnated with some micelles based floor cleaning solution if this gives you the required results then you can complete the job safely, if you need a company in the UK for samples of the above mentioned products to carry out some testing, send me an email with your full postal address and I will have them send you on the required samples.