When someone goes to Las Vegas to play games of chance, there are lofty expectations of winning big bucks and a high probability of huge losses. Games of chance are exactly that. Sometimes you win and most times, you lose.
When installing backerboard, the two parts of the games of chance played by many tile installers are no thinset mortar under the board and no tape on the seams. The time-worn excuse is, “We have done it this way for twenty years and never had a problem.” (That they knew about) This mentality only works as long as your games of chance luck holds out. Beyond that, you are on your own.
Troweling thinset mortar under the backerboard is a requirement according to the TCA Handbook as follows: “Use dry-set or latex Portland cement mortar to establish the supporting plane of the backerboard per the manufacturer’s directions.” In the manufacturer’s instructions, the use of thinset under the board is required to fill the subfloor surface imperfections and provides uniform support for the board. This keeps the board from moving up and down over areas that have low spots which can lead to cracked tile.
Embedding 2” wide high-strength alkali-resistant glass fiber tape (not drywall mesh tape) into the mortar and level with the surface of the board bonds the sheets together to create a single sheet of backerboard. This step keeps the individual sheets from moving independently which also can cause cracked tile as shown in the attached photograph.
All manufacturers require the use of thinset under the board and mesh tape to reinforce the joints. Manufacturers provide these installation guidelines because they have been tested and they work. The most important reason to follow these instructions is because the manufacturers provide warranties that support the installer if a problem arises. The manufacturer can be your best ally when there is a complaint. However, when a suspect installation is inspected that reveals no mortar under the backerboard and no taped seams, the installer is all alone.
With the cost of pennies per square foot to provide both the supporting thinset mortar and mesh tape, is it really worth playing this game of chance? Stop spinning the roulette wheel and hoping it will work. Failure is not an option; do it right the first time.