A ceramic tile floor is about as durable and low-maintenance as you can get... Until it cracks. Maybe you dropped a heavy object onto the floor surface, or maybe the tile is starting to wear because it's 20+ years old. No matter the cause, cracks in ceramic can happen.
Loose tiles are noticed because they produce a distinctive sound when they're walked across, as well as a hollow sound when tapped. Though there are many factors that can cause the loosening of tiles, the most common factors are improper installation or problems with the substrate (level beneath the flooring).
Here are two methods to fix loose tiles - re-bonding or replacement of the tile.
If the tile is loose, but not damaged, one of the most practical solutions to remedy the situation is to inject a substance that will re-bond the tile to the substrate.
1) Using a powerdrill, drill into the grout joints adjacent to the loose tile. Ensure that you apply the correct amount of pressure to drill into the grout, so you prevent the drill from damaging the adjacent tiles. If you do not have a powerdrill, use a chisel and hammer.
2) Use a high-quality, two-part epoxy, mix according to manufacturer's directions, and pour into a construction syringe. Next, inject the epoxy into cracked or damaged area.
3) Dig the epoxy out slightly from each hole and allow it to dry. After drying, re-grout the cracks to level with the existing grout.
If a tile is badly chipped or cracked, then you must replace the tile. Here's how to do it:
1) Use a grout saw to cut through the grout around the tile you wish to replace. Be sure to cut through the center of the grout joint, and to saw completely through the grout. By doing this you will isolate the forces that will be exerted against the damaged tile.
2) Using a masonry chisel (with a 1" to 2" edge) and a hammer, tap the weakest corner of the tile until the corner breaks free. Remember to put the chisel at a slight angle when doing this, and do not exert too much force. You do not want to damage adjacent tiles.
3) Starting from the removed corner of the tile, place the chisel under the lip of the tile and tap it with a hammer. Do so gently and patiently, and you'll be rewarded as pieces of the tile break off. Be careful while doing so, since forcing it may chip or crack an adjacent tile. Repeat this process until the tile is completely removed.
4) Now you need to remove the thinset. But first, you should soften it by soaking the area in water for 15 minutes. Then, you can begin to break off small chunks of thinset, using your masonry chisel and hammer, until the substrate is completely visible. It may also be necessary to use a razor scraper to get the last remaining thinset, providing a clean base for your replacement tile.
5) To replace tiles, skim a thin but even coating of thinset mortar on the new tile with a trowel, then place it into the empty tile space in your floor. Push down firmly on the tile to ensure that it is level. Complete your repair by applying grout around the edges of the tile.
* Tip: Exercise caution during tile removal, as fragments of tile may fly in any direction during the removal. Wear protective goggles to prevent injuring your eyes. Masks are also good for preventing inhalation of ceramic dust, which can be irritating to the throat.
This Old House, "How to Replace a Broken Tile"