A strong base is the key to installing Porcelain tile that remains great looking and crack free. A flat floor is essential. The bane of ceramic tile and natural stone flooring installations is that these products have great strength if a given tile has a solid base under it that will not flex, but if that same tile has a hollow space between it and the sub floor or the sub floor flexes, the tile can easily bend and crack.
The issue of ceramic tiles cracking grows exponentially as the size of the tile gets bigger. Small ceramic tiles can be very forgiving but large (18 to 20 square inch tiles) demand perfect installation conditions if you expect your new floor to remain crack-free.
The most important step is to ensure the surface you are installing the tiles on is in the same plane. The floor does not need to be level, but it must be a perfectly flat. Small humps or depressions in the floor create hollow voids under tiles as you lay them. You must make the extra effort to eliminate humps by filling in all depressions with a floor leveling compound. This process is commonly called “floating the floor.”
A prudent step to take before floating the floor is to check for efflorescence. Efflorescence is the movement of moisture upward through portland cement and concrete slabs. The result of that moisture is a visible white powdery substance that is seen at times on the surface of grout joints. Generally, efflorescence can be cleaned off the tile and joints by a good washing with pH balanced cleaners. In extreme cases, it can be cleaned with acid washing. Do not use any acids other than sulfuric or phosphoric. Use them according to the manufacturers instructions and remember that Portland cements are alkali based. Acid eats alkali. To check for the likelihood that efflorescence might be a problem, tape a small piece of plastic polyethylene film on the slab to be tiled and make sure the tape seals all of the edges. If water condensation appears under the plastic within a day or two, efflorescence will most likely occur. To avoid bonding and grouting problems a waterproofing membrane may be necessary.
When To Begin Grouting
Once the tile has been installed and has dried properly, the grouting process can begin. But, allow tile to set firmly before grouting. Grouting tile too soon, before the setting material has set-up, can lead to problems. Uncured setting material may bleed through the joints and discolor the grout. Also, there is the risk of destroying the bond by shifting tiles, so allow as much time between setting and grouting as feasible. Two days is advisable, but as much as four days might add a level of assurance.
Prior to grouting joints between tiles must be clean and free of excessive setting bed materials. Once the grout has been applied, begin cleanup immediately by sprinkling dry grout over a workable area. Using terry-cloth rags and a circular motion, rub dry grout into the fresh joints. Rub until the joints are uniform and the tiles are clean. A second, very light sprinkling of grout over the same given area, polished in the same manner, will give a perfect joint. This method increases joint hardness, removes excess water, and fills the joints, making them flush with the surface of the tiles. Proceed to the next area and continue grouting in the same manner. If grout film appears, wipe with a lightly dampened sponge, rinsing and wringing it often. Polish floor with a terry-cloth rag.
Damp curing is always recommended to improve the strength of the grout. Cover the finished installation with non-staining kraft paper for three days or wipe the joints with a damp sponge or mop daily, after the initial 24 hours, for a period of three days.