that soap itself is more alkaline in general and that this, in and of itself, is the cause for the damage.   Soap reacts with lime to form an insoluble deposit (soap scum) in " hard water ": 2Na+(R-COO)- (aq) + Ca2+(HCO3-)2(aq) 2Na+(HCO3)-(aq) + Ca(R-COO)2(s) - where R stands for an