1. Space in between the tile and the foundation. This enables movement underneath the flooring. If the movement is severe enough, it can even crack the tiles.
2. The grout was not fully packed into the joints. Tightly packed grout is critical to long term durability.
3. The grout was mixed with too much water. During the drying process, the water in the grout will dissipate, leaving just the right amount to bond with the cement in the grout. If there is too much water, the evaporation process will leave bubbles and holes in the grout, weakening the overall structure.
4. Grout packed on top of other grout, or an additional layer added after drying has already begun. This will ultimately cause the grout to turn rubbery, and it will not become the hard cement block that you need.
So, what do you do when you have cracked grout?
Simply put, you can either live with the cracks or you can regrout.
It is important for you to ensure that when the tile is originally set the grout is packed well, by a professional who knows how to properly mix the grout and properly pack the joints. Also, it is ideal that the underlayment be plywood specifically designed for tile setting or backerboards (often called “Hardibacker”). By screwing the underlayment sheets together, you have the best protection against grout failure later on.
Repairing cracks in your grout are a routine part of regular maintenance of your tile flooring or structure. However, by following the guidelines above you can rest assured that the maintenance will be minimized as much as possible.