Have recently picked up a job finishing a bathroom. I have done construction for over 20 years but have never seen tile this hard! I have drilled hundreds if not thousands of holes in stone, conc, tile, slate,so I have experience. I used glass/tile bits, carbide, and SDS hammer drill bit, 7 in all only managed 2 of the 8 holes I need. Tried start small and work up, tried slow speed with lots of pressure. It's a vertical surface (shower door) so won't stay wet to cool the bit. Installer deceased so I don't know what kind of stone tile it is,homeowner does not know either. Need 6 more 1/4 inch holes to complete. Considering relocating holes to grout joints but would have to re-drill slotted holes in shower frame. Any one been here before?