Whether you are removing all the tiles from a wall or simply replacing one broken tile, all the adhesive must be removed from the exposed space before any further work can be done. Remnants of the old adhesive create an uneven surface unsuitable for wallpapering, panelling, painting or replacement tile. The usual method for removing tile adhesive involves the use of solvents and a lot of scraping, but sometimes these methods fail to remove all of the leftover adhesive. When that happens, you must resort to sanding.
Wait until all the wall tile has hardened if you have made previous efforts to remove it. Two common methods for removing wall tile adhesive involve the use of solvents and heating the adhesive with a hair dryer. Both of these make the adhesive soft and gummy, and you cannot sand off gummy adhesive without gumming up the sandpaper and creating a high risk of damaging the cement board behind it.
Sand down the troublesome tile adhesive on a concrete or masonry wall with a power hand sander using rough-grit sandpaper. You may not be able to set the power sander completely flat on the exposed surface due to obstructions, such as surrounding tiles that you do not wish to scratch, but do the best you can. Only sand concrete or masonry walls in this fashion. If there is cement board under the tile, skip to step 3.
Rub a hand-sanding block with rough grit sandpaper over the stubborn tile adhesive residue, using firm strokes at a steady rate of speed. If you wish to save the cement board, you must sand all of the problematic adhesive with the hand-sanding block, as a power sander will gouge the board. For corners and other hard-to-reach areas, a hand-sanding block will need to be used for all types of walls.
Dust off the exposed surface when you think you are finished. Continue sanding if any adhesive remains.
Always wear a respirator mask when sanding in an enclosed area.