Our new house has very hard water and the glass in the shower is so coated with limescale it's hard to see through. I tried CLR for a few hours with little to no effect. I ordered this material, used 3000 grit and it came right away. Took me a few hours to sand all the tiles but now they look brand new. Be sure to dip the paper in water and rinse the glass while sanding to avoid scratching. I also mixed some dish soap into the spray bottle I used to wash the glass and it made the sanding a lot easier and didn't leave hard water stains.