Hello. I have made around thirty-five 4 inch tiles of a terracotta clay body. The backs are unglazed and porous... and not very heavy. I want to tile the inside of an arch between my kitchen and living room. The surface of the arch is satin paint over a meager amount of "orange peel" blown on texture, which in turn, I believe, covers whatever one would have used to form an arch. I am concerned about the upside down part of the arch and whether a mastic, or a thinset would most assure that the tiles would adhere? Also, do I need to worry about the tile and adhesive pulling the painted texture off? I would appreciate any ideas you might have. Thanks... Cherel

You should scrape off everything until you get down to the paster or drywall. Do not use thinset with these tiles. Mastic or modified thinset would work better.