What Causes Loose Ceramic Wall Tile?

Wall tiles become loose when water seeps through broken grout lines  that usually are installed over sheetrock. The solution is to replace the tile and backer board. Contractors either float concrete walls, use a cementitious backer board, or claim to use (greenboard) waterproof sheetrock.  Waterproof sheetrock does not exist. The correct term is moisture resistant sheetrock (M.R.sheetrock). Gypsum is not waterproof. The green paper on M.R. sheetrock makes it resistant to moisture. Grout absorbs moisture. Cracks in the grout absorb water. Water absorbs into the sheetrock like a wet sponge, eventually making the sheetrock fall apart.
   
Cementitious backer board (Wonderboard, Glasscrete, etc) is composed of a light weight cementitious material, half inch thick with a fiberglass mesh on each side. If water penetrates cracked or missing grout, the board absorbs the water without falling apart. If tile loosens up and falls off the wall, the adhesive can be scraped off the board; Apply new adhesive to the tile and place it back on the board.

Houses are constantly in motion, continually expanding and contracting with the forces of nature. Some houses are more stable than others. An easy way to tell how stable your house is by looking at your ceramic tile wall and floor seams. A seam is where a tile wall meets another wall, tiles meet the tub, tiles meet the floor, or any wall adjacent to the tiled surface. Expansion and contraction of your walls and floor place stress on seams causing grout to crack. Grout will sometimes crack in random areas due to stress created by the wall studs or backer board seams (where sheetrock joins other sheetrock etc.). To rectify this problem, I substitute silicone for grout on all the wall seams and use a flexible sealant, thus creating expansion joints at all the crucial areas. 
   
Silicone has a rubbery yet firm consistency that resists mildew and sticks well between tiles. Acrylic latex caulking is commonly used by contractors. Acrylic latex doesn't have the elasticity of silicone, tends to mildew faster, and shrinks as it dries. Acrylic is water soluble and easy to work with. Silicone is a petroleum based product that is more effective, yet harder to work with. I have approximately 15 years working experience applying silicone neatly and efficiently. Neatness counts: the less silicone you apply the neater the job. Potential problems are easier to spot when you don't have globs of silicone smeared all over the tiles.