Expansion joints, also known as movement joints or movement accommodation joints, are critical to the success and longevity of ceramic and porcelain tile installations. They are probably the least used, most misunderstood and one of the most important listings in the Tile Council of North America (TCNA) Handbook.
Without them—especially on floors subject to sunlight—most installations which otherwise appear to be done well will fail. Allowing little or no room for the tile assembly to expand causes the tile to pop up or “tent” in the middle of the floor. This situation occurs in both commercial as well as residential jobs, so neither of them is exempt from this requirement.
The Handbook statement is very clear: “The architect or designer SHALL show the specific locations and details of movement joints on project drawings.” Given this sentence, where does the misunderstanding begin? Many people involved in the installation of tile products don’t understand the tile does move. If this expected movement is not accommodated, the tile will become rebellious and most likely very expensive to the responsible person or company.
The attached Handbook detail (EJ171) shows the necessary components of the movement joint. Notice that the elastomeric sealant is attached only on the sides of the two adjacent tiles. One critical point here is the sealant does not contact or bond to the bottom of the joint. In this case, the insertion of a “rounded back-up,” or foam backer rod, allows the concrete floor to expand and contract. However, its primary role is to keep the sealant from touching and bonding to the bottom of the opening.
Think of the movement of the sealant like the action of an accordion: in and out. It will also allow the tiles to move in a back-and-forth motion similar to rubbing two hands together. However, these two movements can only occur if the sealant is bonded just to the tile edges. If the sealant is allowed to contact the two sides and the bottom, it is locked in place and will have zero movement ability.
Once these principles are understood and the joint properly installed, expansion joints will permit this required movement to take place and keep the tile flat on the floor where it belongs.