Ceramic tile and the grout between the tiles on a floor create a rigid horizontal mass of material. It is difficult to imagine this mass of material expanding and contracting because of external factors such as temperature and relative humidity, but it does. Installed correctly, ceramic tile floors make allowances for the movement of the floor over time. Expansion joints are areas of space between rigid surfaces that allow for expansion and contraction of materials.
Floor-to-Wall Expansion Joints
When you install ceramic tile on the floor, you must take care to create an expansion joint between the walls and the tiled floor. The Tile Council of North America recommends at least a quarter-inch gap between the tile floor and the walls. Never fill this gap with grout, because tile grout is not flexible. Instead, fill it with an elastic material capable of sustaining the movement of the floor and the movement of the wall. Caulking is the best choice for this application.
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Always install the ceramic tile floor before installing the wall baseboard trim. You must be able to caulk the space between the wall and the ceramic tile floor. Normally this area is underneath the baseboard trim.
Expansion Joints in the Floor
If the ceramic tile floor is wider or longer than 25 feet, you will need to install an expansion joint near the center of the floor. Caulk the grout gap between two adjacent rows of tile all the way across the floor. Install the caulk after the tiles have been set and before the grout is installed. Plan well to avoid mismatching the color of the grout with the color of the caulk at any mid-floor expansion joints.