Concrete is a good subfloor for tile when it is prepared properly. The concrete needs to be in good condition before tiled is installed on top of it. If not, the tile will crack and break in the same areas where the concrete is damaged. The concrete also needs to be perfectly clean and totally dry before you can tile over it. The average do-it-yourself handyman can prepare the concrete for tile without a lot of trouble and with only a few tools.
Sweep the floor to remove any debris from the concrete. A good shop broom will work well.
Mop the floor with clear water to remove any dust that may remain. Let the concrete dry a minimum of 1 hour before you proceed. The levelling compound--that you will use to level out any unevenness in the floor--will not stick to the concrete if it is dirty, which will cause the tiles to come loose.
Repair any cracks in the concrete. Spread a 30-inch wide strip of thin-set adhesive--a type of concrete that will support the tiles and prevent them from cracking--over any cracks in the concrete. Cut and then place a 24-in. wide strip of isolation membrane, also called anti-fracture membrane, over the crack. Isolation membrane will absorb the shock--rather than the tile or the thin-set--of everyday stressors such as walking, running, dropping things, the weight of furniture, etc. Spread out the membrane with a flat trowel, forcing the membrane into the thin-set. Feather the edges. Let this dry per the labels direction before proceeding to the next step.
Apply a latex primer onto the concrete with a paint roller. Primer is available at your local tile or home improvement store. Let the primer dry completely before proceeding to the next step. Although 24 hours is usually time enough for most primers to dry, refer to the package label for the drying time for that particular product.
Move a 4-foot carpenters level around the floor. Look for any gaps that appear between the bottom of the level and the concrete. This will show you where any low spots are in the concrete. Mark the low spots with a marker.
Mix the self-levelling compound in a 5-gal bucket with cold water. Follow the specific instructions listed of the levelling compound packaging. Use a drill and a mixing paddle. You have only 15 to 20 minutes of working time once you start to mix the compound, so mix up only 1/2-bucket at a time. After 20 minutes, the compound will start to set and form chunks of dry compound in the compound. A self-levelling compound is a very thin concrete mix that will level out small dips in the floor.
Pour the levelling compound over the areas you marked previously. The levelling compound spreads out on its own to raise these areas to the level of the rest of the floor.
Spread out the levelling compound with a flat trowel to help it distribute itself. Let this dry completely. Most levelling compounds are totally dry within 6 hours, but to be safe, allow it to dry overnight.
For safety, wear protective eyewear and gloves, and a disposable mask, with mixing with thin-set. For comfort, wear thick knee pads when working on concrete.