Hi Trevor
Its not grease on those floors its ground in soil from regular mopping with kentucky mops and high alkaline floor cleaners, the acid we used is food grade and not hydrocloric, for cleaning and maintaining hard surface floors on a daily basis, we recommend to use waffle microfiber floor cloths and a floor cleaner of between 7 to 9 on the pH scale and guaranteed those problems will never again happen, trust me it took 25 years to discover the solution to this on going problem in the cleaning industry.
Kind regards
Tadgh