In production homebuilding, it’s common to make the mistake of not paying close attention to the floor installation. Blame it on rushed schedules, costs, or confusion about who’s responsible for ensuring the floor covering is ready for installation. Whatever the reasons, when tiles are installed too soon, problems like grout stains, poor adhesion, and cracks can develop.
Grout stains: A sign of moisture in a concrete slab
Grout stains typically occur when tile is installed over a slab that hasn’t fully dried. It’s common to think that a slab is dry once it has cured. However, a slab can continue to release moisture for up to a year after it's placed. Tiles installed over a wet slab trap moisture, providing only one escape route—through the grout joints. As moisture moves through the joints, it chemically reacts with grout and causes staining. Moisture under the tiles can also cause the adhesive to break down and the tiles to detach from the floor.
It’s important to test the vapor emission of the slab before the tiles are installed. A calcium chloride test is the accepted industry standard for testing vapor emission. The vapor emission shouldn't exceed 3 pounds per 1,000 square feet in 24 hours. If it does, wait to install the floor covering.
Poor adhesion: Proof of poor tile setting techniques
Many tile problems are caused by a poorly applied tile adhesive. A layer of tile adhesive locks the tiles into place, but only if it’s applied correctly. Tiles can’t bond to the adhesive if the thickness varies, the ridges are inconsistent, or the adhesive dries before the tiles are installed. Make sure you apply an even layer of adhesive, use a trowel with an appropriate notch size, and install tiles while the adhesive is still wet.
Tile cracks: Evidence of movement in the floor
Tile floors crack when they’re not protected against movement in the slab or other materials that touch the tile. The key to preventing tile cracks is to provide a buffer between the tile and other surfaces. A great way to do this is to install an isolation membrane over the concrete slab. In addition, separate tiles from perimeter walls, penetrating pipes, and kitchen and bathroom cabinetry with a ¼” gap filled with backer rod and silicone caulk. These expansion joints will provide space for materials to expand and contract without putting stress on the tile and cracking it.
The most important part of any tile job is the prep work. When the slab is level and dry, it will provide better support for the tiles. A tile floor that is adequately protected against water intrusion and expansion and contraction will be less likely to experience grout stains, poor adhesion, and cracks—problems that lead to customer complaints and rework.