If you’d like to avoid tenting, cracking and broken tile on your projects, learn all you can about movement joints. Construction materials will experience motion and sometimes they move a lot or very quickly due to factors like thermal cycling or deflection.
Entire buildings expand and contract, concrete slabs move due to live and dead loads, they sag or creep over time, and even well bonded tile can crack and come right off the surface. Tile assemblies should be designed to withstand dynamic forces by moving along with them. Soft, flexible joints within the tile assembly help to accommodate inevitable expansion and contraction. Movement joint fillers will absorb compression during expansion, whereas tile and grout are not designed to compress. Flexible sealants return to their original size after compression from tile expansion, over and over, or day in and day out; this is referred to as cycling. Throughout this video, we will be turning to Detail EJ171 - Movement Joint Guidelines in the Tile Council of North America’s Handbook for specific information. EJ171 begins: “Perimeter and field movement joints within a tile installation are essential and required.” That phrase is the single most important takeaway on this topic. These soft movement joints are installed at changes of plane and set intervals based on project conditions. Joints in the slab are also honored when carried up through the tile assembly. A construction or cold joint is formed between placements of concrete during the pour. Control, contraction or saw cut joints are added during or shortly after placement to help regulate expected cracking during curing of the slab. Expansion joints are created at adjoining parts of a structure to accommodate anticipated expansion beyond contraction. Isolation joints are located at changes of plane, such as columns, where vertical movement is expected. Joints that are designed to move out of plane should NEVER be covered with ANY type of floor covering. According to TCNA, all of these joints are considered active and must be carried through the tile assembly. That means creating soft, flexible joints at the same width as those in the slab directly below. Here are the default placements in each direction: For interior spaces, the maximum allowance is every 25-feet. When interiors are exposed to direct sunlight or moisture, the (requirement doubles;) spacing comes down to every 12-feet. For an above-ground slab, which can expect higher levels of deflection, the maximum spacing is also 12-feet. Due to anticipated thermal expansion and water exposure, exterior applications require movement joints every 8 - 12-feet depending on materials and conditions. Perimeter joints are always required at walls, changes of plane, or any restraining surface, including other floor coverings, especially over wood framed construction. Joint widths are calculated with a formula based on the linear thermal expansion of the tile. For exteriors, the minimum width is 3/8-inch. Some interior joints can go as narrow at 1/8-inch, but ¼” is preferred and is required for perimeters or areas exposed to sun or moisture. Use a sealant that is color-matched to your grout. And, the joint filler needs to remain permanently flexible, so choose a 100% solids silicone sealant that complies with ASTM C920. On commercial projects, the minimum joint width is typically no less than a quarter of an inch, and the ratio of width to depth is 2:1. ASTM C1193 details how the joint should be properly filled. Placement of movement joints is crucially important for successful tile installations and to maintain a good reputation for our industry.