I'm having some difficulty cleaning some very VERY stubborn calcium tile staining emanating from a rockfall. I used acid, but had to use so much to get the job done that it partially consumed some grout. This time around I'd like to try bead blasting since I have access to a portable blaster. There are services in town that do just this, so I figure it will work, but I'm conerned about the proper way to go about this. I've heard that bead blasting can ruin glazed tile? Any suggestions?