Figure 1 shows a familiar sight of a cracked tile. While the installation of movement joints will normally prevent such cracking, a particular problem can result from the tiles bridging a board joint over a timber substrate.
In some cases it is simply just not practicable to insert a movement joint over every joint in the floor, especially if the joint or crack is irregular.
Adhesives used to adhere tiles rely on a strong bond to keep the tile firmly fixed to the substrate. But this type of bonding can pose problems with the transmission of shear stresses to the surface covering, particularly where there are board joints in the substrate. A solution would be to remove the shear stresses between the substrate and tile using an uncoupling system.
The British Standards recommend isolating a rigid covering, such as ceramic tile or stone, from the substrate, which is dealt with in BS 5385 Part 3. This states that failures arising from variable stresses can be avoided by isolating the tile bed from the base by using a separating layer which prevents the two elements from adhering to each other, and thus allows each to move independently.