Movement Accommodation and Joint Design
Movement Accommodation and Joint Design
All tile installations move due to thermal expansion, moisture changes, and structural deflection. Large format tile requires movement joints to prevent cracking and tenting. Key joints: perimeter joints (at walls and fixed objects), field joints (within the tile field), and expansion joints (over structural joints). ANSI A108.01 and TCNA EJ171 specify that movement joints are required at intervals of 20–25 feet for interior installations and 8–12 feet for exterior. For LFT, these intervals may be reduced. Joint width should be at least 1/4 inch and filled with a flexible sealant (e.g., silicone or polyurethane) that meets ASTM C920. Traps: omitting perimeter joints; using grout instead of sealant in movement joints; and placing joints too far apart. Worked example: A 30-foot long room needs at least one intermediate movement joint at 20–25 feet. If the room is 40 feet, you need two joints (e.g., at 13.3 feet and 26.6 feet). Perimeter joints are required at all walls. Use a backer rod and sealant.