If you have recently installed ceramic tile on a wall or in your bath, we recommend you save the leftover tiles for future repairs. One of the major difficulties in repairing a tile is matching the existing shade with a new tile. The second difficulty is the drywall behind the tile. If it has also been damaged you will need to have the drywall repaired before installing the replacement tile, and you may want to have this done by a professional.
The first step is to remove the broken tiles is to use a grout saw or utility knife to remove the grout around the tile(s) that have been damaged.
Now you can shatter the broken tile using a chisel and hammer - you should use goggles and other necessary precautions to prevent injury at this time. Once you've removed the pieces of tile you should scrape off any remaining grout and/or adhesive, but be careful not to damage the drywall.
Once you have the surface as clean as possible (and ensured the drywall is not damaged) you can begin installing the replacement tiles. If you are just replacing a single tile a standard silicone adhesive can be used. However, if you are doing a multiple tile replacement it would be best to use the same adhesive as the rest of the wall. For the best results try to apply just enough adhesive to ensure the replacement will be level with the existing tiles. Now you can press the tile(s) into place, wipe off any excess adhesive on the surface and tape the tiles in place to allow it to set. Let the adhesive set as long as required by the manufacturer's instructions.
Finally, you can apply grout to the joints between the tiles. You should try to match the new grout to the existing grout, and you may be able to get the right shade available pre-mixed. Excess grout should also be wiped off, and the joints shaped, using a sponge. This is a great time to regrout all your tiles, refreshing the appearance and making the repair less noticeable.
Tiles should be resealed once in a while to prevent moisture from getting in. Otherwise, the moisture may cause damage to your underlayment. The grout should also be regrouted at this time, or replaced entirely if it has become moldy. First you should clean the grout joints. Any dust or dirt that may be found in the joints must be removed before you can begin to regrout your tiles. After cleaning, you should allow to the area to dry, then apply a silicone or a water-based grout sealer. If you get grout sealer on the actual tiles it should be wiped off prior to drying. If there are cracks in your existing grout, it may mean a possible moisture penetration and damage of your underlayment. You need to examine it to determine if you need to make repairs, especially if your underlayment is drywall. If the cracks are small and appear clean you can simply apply new grout to the joints. However, if the cracks are big, or if there is mildew present (in either small or large cracks), you'll need to first remove out the old grout. You can do this by simply using a utility knife and then begin regrouting.
Proper maintenance of your tiles and grout is the best way to prevent any need for repair, as well as ensuring that your tile walls retain their beauty for years to come.