Ceramic tiles are made of clay and glazes. They are highly heat resistant and can withstand wear very well, but much of their integrity depends on the surface to which they are bonded. The weakest point of ceramic tile is the adhesive used to attached the tile to the floor. This is why manufacturers recommend that floors be completely even and clean before tile installation. If you have ceramic tile on a bulging or uneven floor, this creates a number of serious problems.
If a floor is bulging or uneven in the first place, this points to a moisture problem. Moisture will warp the subfloor and joists, creating this undependable surface. This type of moisture creates many problems. Not only will the ceramic tile adhesive and grout become weakened in the presence of moisture, but moisture can encourage the growth of mould in crawlspaces and indicates a leak or insulation problem in the house.
Adhesive is designed to bond the ceramic tile to an even floor. Ceramic tiles are flat, and the adhesive cannot make up the difference when the tiles are installed on top of bulges or other awkward surfaces. The end result is adhesive failure, where the bond breaks between the ceramic tile and the floor. The ceramic tiles become dislodged and must be replaced.
Grout can also suffer from uneven floors. Grout is essentially a mortar, and if it is placed on a warping floor it will eventually crack. Not only does this weaken the hold ceramic tiles have, but it also provides a way for moisture above the floor to seep in and cause even more damage.
If you have ceramic tile that is cracked and uneven, it may have been installed on a bulging floor. It is also possible that the tile itself is to blame. This is not as common as flooring issues, but ceramic tiles do expand and contract throughout the seasons, and if they do not have a slight amount of room to move and adjust, they can warp free of the adhesive and create problems.