There are several reasons tile flooring can lose its bond and buckle. Properly diagnosing the cause of the problem is essential to ensure any fix will have a long-lasting effect. After determining the root cause of the buckling tile, it's possible to fix all problem areas and protect your investment from future damage.
Floor Expansion or Shrinkage
Tile is a porous substance; therefore, over time it can swell with high moisture. With enough expansion, the pressure can cause the tile to pop up, resulting in a buckling floor. Alternatively, it may be the floor that has expanded and taken the tile with it. Floor substrates are often composed of a more porous substance than tile. The result is the floor my swell with moisture and humidity changes faster than the tile. Shrinkage can occur for the same reasons but in reverse. Tile or a sub-floor set in a humid environment may shrink if humidity is reduced for an extended period. Shrinkage can also occur due to the natural compacting of concrete as it cures or due to building load as it ages. For either shrinkage or expansion, the answer is to leave a perimeter expansion joint around the outside of the tiled room. This is a gap between the last tile and the wall that is not grouted or tiled. In large rooms, such as those wider than 20 feet, an internal expansion joint is a good idea. This would consist of not grouting between two rows of tile. Instead, fill this area with a specially formulated expansion joint caulk. You can use 100% silicone caulk, but it's available only in limited colors.
Using Old or Dusty Tile
Old tile may become brittle or shed ceramic dust. This causes the same problem as dusty tile in that the bonding agent used to affix the tile to the floor substrate will not form a secure bond. With the addition of other slight environmental stresses, such as humidity, the bond will lose its grip and the tile will buckle. Therefore, always use clean tile in good condition.
Improper or Poorly Mixed Bonding Material
The bonding material, also known as mastic, used to adhere the tile to the floor needs to meet the requirements of the work site. For example, plywood requires a different type of bonding agent than concrete. Similarly, outdoor applications call for different bonding agents than indoor installations. Make sure you use the proper mastic for the substrate and location. If a dry powder bonding agent was used, check to see if it was mixed properly. Small pockets of dry dust in the mastic will indicate a poorly mixed bonding agent. Always follow the mixing directions.
Some sub-floors are not appropriate for tile. Although you can use plywood as a sub-floor, it needs to be a minimum of 3/4 inch (preferably thicker) for large areas. Otherwise, the plywood will flex, which will ultimately pop and buckle tiles.
Improperly Set Tiles
Large or oversized tiles require a certain troweling technique to ensure they achieve a strong bond with the mastic. All tiles need a gentle whack with a wooden object when being installed to set them in the mastic. If not properly installed, tiles will pop off the sub-floor. If troweling lines are visible in the mastic below popped tiles, a sufficient bond was never achieved during installation.