I think it is acid, erebus. Does it say to wash brushes afterwards with water or white spirits?
I used slightly different stuff for a similar reason - apply it, wait about 10-20 minutes, then agitate it with a brush and wipe it off. Sometimes you need to repeat it until the layers of stone sealant or polish come off. Wear gloves as it numbs the tips of your fingers.
Give the area a good wipe over with meths afterwards and it should be completely grease free.