Andrew Coote
Hi Clay Rafal and Martin suggested getting someone in to assess your problem - that is the only way to be sure of the cause. Here are the most common causes: 1. Tile is too heavy to be supported on the surface onto which it is tiled. An 8mm thick tile weighs about 16kg per square metre - and tile adhesive weighs about 4kg per square metre. Plaster on walls can only hold a weight of 20kg per square metre - so if your tiles are thicker than 8mm the plaster may have been pulled from the wall behind. 2. The walls behind the tiles are damp causing the adhesive to fail. Often happens in shower areas when people tile without waterproofing the surface to be tiled because they believe tiling provides waterproofing (it does not).Can also happen where damp from outside is affecting wall. 3. The walls had PVA applied before they were tiled. PVA has an opposite pH value to tile adhesive - so if someone mistakenly applied PVA to the walls (thinking it was a primer) then the adhesive never set. 4. The walls were painted and the paint has failed - so the tiles are no longer stuck to the wall. Many tilers will always remove paint from walls before tiling because emulsion paint in bathrooms is notorious for peeling off walls and causing tiles affixed tiles to fall off. So post the job - you may get free assessments if you advertise the job as a re-tiling (if the tiles are starting to fall off I recommend take all the tiles off and re-tile). That not only solves the problem properly but gives you a chance to redecorate at the same time.
