Been reading some conflicting information regards tiling on painted walls, so advice please. I'm looking to tile a small feature wall in a lounge (so not subject to moisture - approx 2.3m x 1m) using porcelain tiles, 150mm x 900mm x 9mm tiles with a rapid set flexi adhesive. The wall is plasterboard previously skimmed and painted. The paint is in good nick, no flaking, and other than a couple of very small areas survived a duct tape test and I've also used a sander. The conflicting bits I've read is whether to next scratch/score the area and also if a primer also needs to be used over the area (I've got SBR Bond if needed). Weight of tiles & addy is approx. 20kg per sqm. Last question, should I back-butter the tiles? Thanks in advance.