We have a feature wall made of bejmat tiles (which are unglazed zellige tiles, which are hand made clay tiles). Although they are fired in an oven, they do chip relatively easily. Having said that, our tiler did a fantastic job of putting up some 30m2 and they look great. I now want to put up some paintings and need to drill into the wall to install screws etc. If I damage the tile it probably won't matter as the painting will cover that bit of the wall anyway, but I still want to try to avoid damage as the wall is sound proofed, so I rather make my penetrations as small as possible. The tiles are about 14mm to 17mm thick (they are all irregular) and the grout lines are about 2mm thick. I'm thinking that the best option would be to drill into the grout where four corners meet. What drill bit size and raw plug should I be using and what depth hole and screw should I be using? Behind the tile there is plasterboard (this is not a bathroom or kitchen, just a feature wall in a lounge) and then 10mm of a honeycomb board filled with sand (for soundproofing) and then a void filled with mineral wool sound proofing. The paintings we want to hang are about A1 in size and probably weigh around 5kg. I'm hoping one sturdy screw will be enough per painting.