Questions often arise regarding what constitutes a suitable substrate to which ceramic tile can be bonded. A number of sources can help you determine whether or not your surface is suitable and also advise you on how to prep these surfaces.
The two publications most commonly consulted for this information are the American National Standards Institute (ANSI) A-108 and Tile Council of America (TCA) handbook. Other valuable sources of information include the National Tile Contractors Association (NTCA) and the Ceramic Tile Institute of America (CTIOA). All of these organizations will steer you in the right direction.