Hairline cracks can develop in porcelain tile due to cracking in the concrete surface under the tile. The expansion and contraction of the concrete will put a strain on the tile and cause reflective cracking. Using a crack suppression membrane will stop these stresses from transmitting and protect the tile from hairline cracks.
Concrete has control joints that allow the surface to contract and expand, thus avoiding cracks. It’s possible to avoid hairline cracks in the porcelain tile by continuing the control joints through the tile. This method is recommended by the Tile Council of North America, as it prevents hairline cracks in the tile from developing if the control joints move. Unfortunately, no particular method for tiling over the control joints has yet been recommended.
Cracks in Concrete
If there are cracks in the concrete over which you’ll be tiling, you need to fill them before doing anything else. Once they filled and the surface is level, give it ample time to cure before moving on. That means several days rather than hours. By taking longer over this part of the process you lessen the likelihood of future cracks.
A crack suppression membrane performs 2 functions. It shields the tile from any movement in the concrete, which is its main job. It’s also waterproof, so it stops moisture from inducing cracks.
There are several ways to apply the membrane to the concrete. As it’s water-based, you can use a sprayer, roller, or a trowel. Roller and sprayer lend even coverage and takes less time.
Ensure that the concrete floor is completely clean. Sweep it thoroughly and then use a wet/dry vacuum. In some instances, you might also want to mop the floor and leave it to dry. Be certain to clean out all the corners, edges, and crannies on the concrete floor.
If using a roller, decant the membrane into a roller tray and cover the roller. You don’t need a very thick coat, just enough to give complete coverage on the floor. Start in the far corner of the room and work outward from there. It will be much easier if you work in sections, moving gradually toward the exit from the room. After finishing each section inspect it to ensure all the concrete has been covered. After finishing the room, leave the membrane to dry.
Once the membrane has dried, lay the porcelain tile as you normally would, using reference points and working from the center of the room. The thinset will adhere to the membrane, which will prevent hairline cracks in the tile.