Hi, I’ve had a niche built in my shower (photo on left) I’d like a shelf inserted in the middle (similar to the top right photo) and I’m wondering the best way to do this. My plan is for the sides of the niche to be tiled in the same ceramic tiles as the shower and the back of the niche to be tiled in glass scallop mosaic tiles (lower right photo). I’ve been told it will be tricky to cut a slot into the mosaics to insert the shelf, due to their scallop shape. I’ve read that when you drill in shelf screw anchors the holes breach the waterproof membrane, which even if sealed I’d rather avoid. As the niche hasn’t been tiled yet I’m wondering if the shelf (27cmx11cm) could be embedded into the mortar and grout? Would embedding into the two side tiles be strong enough without embedding into the back mosaics? All advice welcome! Many thanks