As I've written previously, all concrete slabs are not created equal. They all may look and feel the same, but they are not necessarily identical. On-grade slabs are never truly dry. Even a seemingly bone-dry slab that's been coated with a curing compound can be deceiving. In actuality, that curing compound can dramatically inhibit evaporation of water from the concrete.

In any event, if a curing compound has been used to slow down water loss as a means of enhancing the curing process, it is incumbent upon the flooring professional involved to remove the compound before he proceeds with a ceramic tile installation. Failure to remove the curing compound virtually ensures a loss of mortar bond at some point in the future.