As with all the other types of surfaces, that you will be installing tile, the new tile installation cannot be compromised by an unstable base surface. Therefore, if a concrete slab is cracked and spalling, it must be repaired. The best method for repairing a crack in a concrete slab, is to open the crack up by chiseling, hammering or using a masonry router to produce a V type joint, where the crack was. A V type joint, is a joint that is larger at the top and smaller at the bottom. There are manufactured and designed mortar mixes, which are used to fill in the V joint to bond together the two sides of the joint. This application should be done with a minimum of water, and the installation must be carefully applied, to ensure a consistent and complete filling of the V joint. If the concrete slab is spalling, which means the top of the concrete slab is breaking apart and separating, then this compromised material must be chipped off and cleaned. In this situation a full covering of thin-set material is recommended to be either poured or troweled over the top of the compromised slab. Manufacturers have developed special products that can be mixed and poured over the top of the slab surface and are what is referred to as “self-leveling”. These products will seek their own level, and provide a uniform, consistent and stable