Used this product on a rental property of mine and the showers were caked with rust & soap scum. I used CLR, Lime Away and wasted my money. I bought this and voila' it melted the hard water deposits, rust & scum right off the walls with a scoaring pad. Spray it on wait about 3 minutes and presto, you can see the scum melt. Hope this helps those doubting thomases out there, it changed my mind :).