Hi. I am planning tile on tile job, by laying glass mosaic tiles on existing glossy tiles in the bathroom shower area. The materials I have bought are Mapei Eco Prim Grip, Mapei Aquadefence for membrane. I also tried to remove glossy surface with sanding machine (240 grit), but didnt notice any difference - the old tiles are still smooth and shiny. Today, I tried to apply the primer Mapei Eco grip for a couple of tiles, and afer a few hours I tried to remove it with a rag and some water. And it was gone. Is it supposed to be like this? I imagined it would stay even with application of water. Or am I doing something wrong? I really dont want to have the job done and then see the tiles to fall over the wall. Please advise. Thanks everyone.