The joint is the space left between the floor tiles or between the floor tile and another structure, such as a wall, stair post or bathtub. An expansion joint is required when you're working with certain types of tile, such as ceramic or stone tiles. These materials have no flexibility or give. As the areas surrounding the tile expand and contract, the expansion joint allows the floor tiling to do so, as well, since the actual material of the tile cannot.
Install all of the floor tiling except for the areas that will need expansion joints. These tiles will be installed adjacent to a hard surface or structure, such as a wall or column.
Insert a closed cell foam backer rod into the floor tiling expansion joint. This material presses right into the joint to allow for additional expansion.
Look for the appropriate expansion joint material for your floor tiling. You will need a flexible silicone caulk with a minimum hardness level of 35.
Apply a bead of the silicone caulk over the backer rod. The bead needs to be thick enough to cover the entire joint. Smooth it over with your finger for a more attractive finish to your tile floor.