There has been considerable discussion concerning the need for movement joints in tile assemblies. The question is not whether they are needed; that is a simple yes. The questions are “Where do they go?”, and “What is used to fill the joint in the tile assembly that will control or compensate for movement in the entire assembly?” There are several different types of construction movement joints defined by the Tile Council of North America (TCNA) that are needed in tile assemblies:
- Construction / Cold Joints are formed between two successive placements of concrete. Quite often the reinforcement in the concrete will continue through the two successive placements.
- Contraction / Control Joints formed in the concrete or sawn into the cured concrete. This creates a weakened plane in the concrete that regulates the location of cracking from natural movement during the curing cycle. The concrete will crack the same as the random cracks we commonly observe in concrete slabs, except with the inclusion of control joints, this random cracking is controlled to a specific location. There is a potential for continued movement that will cause these cracks to open and close the same as the unrestricted natural cracks that occur randomly.
- Expansion Joints are created in the concrete to compensate for excessive expansion, due primarily to temperature changes in the concrete. As the concrete cures it generally will shrink and as the temperature raises the concrete and tile assembly will expand. When the expansion exceeds the shrinkage the concrete needs a joint to compensate; if not it can bend and dome slightly, resulting in cracks in the assembly.
- Isolation Joints are typically found where two concrete surfaces meet. Most common is when a horizontal surface meets a vertical surface. Since these surfaces can move in three dimensions, it is important to isolate each from the other.
American National Standard Specification for the Installation of Ceramic Tile (ANSI), with the approval of TCNA members, has defined the size and frequency of movement joints for a successful tile or stone installation.
The placement and size of the joint is dependent on the environmental conditions at the location of the concrete. If the concrete subfloor is interior in a controlled environment there should be a movement joint place every 20-25 feet, in both directions. If that interior space is exposed to direct sunlight and will therefore have more significant temperature fluctuations the joints should be more frequent; every 8-12 feet. If the tile is to be placed over concrete in an exterior application, the concrete and tile assembly should have movement joints placed every 8-12 feet. In applications where the tile assembly will be exposed to temperature changes up to 100°F the width of the movement joint should be 3/8″ to 1/2″ depending on frequency of the movement joints. The width of the movement joint should be increased by 1/16″ for every 15° F increase in temperature change above 100° F. Generally it is acceptable for the movement joint width to equal the width of the grout joint in interior applications, but never less than 1/8″. The movement joint width in the tile assembly should never be narrower than that placed in the concrete subfloor.
The movement joint in the tile assembly should be placed directly over the movement joint in the concrete substrate; exceptions to this will be discussed later. The identified movement joint in the tile assembly should not be grouted with the cement based grout; it is to be kept open during the grouting process. Once the grout in the balance of the assembly has fully cured, generally 48 hours, the identified movement joint should be cleaned out of residual debris; i.e. dried grout, dried mortar, dirt, etc. A suitable backer rod shall be compressed into the open joint to within one half the width of the joint of the surface of the tile; if the movement joint is 1/2″ wide it should be filled to within 1/4″ of the surface of the tile with the backing rod. Suitable backing rod materials are defined in the ANSI specification as; closed cell polyethylene foam, closed cell butyl rubber foam, and open or closed cell polyurethane foam.
Once the movement joints are properly prepared they are now ready to be filled with the right flexible caulk/sealant. Using the wrong caulk will ruin the tile installation; the right caulk is one that will move with the tile assembly and hold up to the abuse of daily traffic. If the wrong caulk is used in the movement joint the stress that can develop in the tile assembly, from movement of the substrate, can damage the tile assembly. The damage can be as minor as cracks in the cement grout to major cracks through the tile or loose tile. It is tempting to use a low cost siliconized acrylic. These are generally available in a variety of colors and while they can be used to fill the space where horizontal surfaces meet vertical surfaces in some installations, they do not meet the ASTM C-920 requirements nor provide the performance required for a movement joint in most specified tile installations. Siliconized acrylics do not have the flexibility to move with the assembly in commercial application. ANSI recommends the use of a Silicone, Polysulfide, or Polyurethane Caulk that meets the requirements of ASTM C-920 for filling the movement joints.
Silicone caulk has many advantages over the other two:
- Available in a wide variety of colors.
- Better stain resistance to common materials.
- Better UV stability for exterior applications.
- Excellent bonding to glass and glazed surfaces of tile.
- Shorter tack free time, speeds full installation.
- Can withstand a greater environment temperature range.
For successful ceramic or stone tile installations it is imperative to incorporate movement joints in both the concrete substrate and the tile assembly. Ignoring the need for proper movement joints in the tile assembly will result in call backs and expensive repairs and the subsequent installation of movement joints. It is important that the ANSI and TCNA guidelines are followed for the proper placement of these movement joints. It is equally important to use the right materials meeting the requirements of the industry standards. To meet the appeal of today’s designers it is important to use a movement joint sealant/caulk that matches the color of the cement grout used throughout the