A few tiles in my building flat give a cracking noise when i step on them.Upon inspection i found that the tiles make cracking sound even when i press them with my hands but requires some strength.There is a small airgap in a few joints but the gap is very small.The tiles were installed almost 15 years ago and i dont know how old the building is but is considered an earthquake proof structure.The cracking sound is sometimes even for as long as 1-2 seconds when standing on it.So is it a lose tile or a foundation crack?
It sounds like the tiles has become loose. There is a chance that the subfloor may be loose as well depending upon what it is made out of and how it was installed. Wood subfloors can become loose if they are nearly nailed down and not screwed down. The best thing to do at this point is to take up the floor and inspect any problems with the subfloor and make any repairs. Then install new tile. If you want to save a few bucks you can take up just the ones that are loose and install new tiles that look best in their place.
You say the tile floor was installed about 15 years ago, which would make me think that the thin-set mastic used to adhere the tiles to the floor has dried out and allowed several of the tiles to loosen on the mastic bed. This allows them to move, albeit ever so slightly, each time you step on them. If the problem is not resolved soon the cracking sound will increase and there's a good chance the tiles themselves will crack and then need to be completely replaced. This could be sort of difficult seeing as how you'd be attempting to match 15 year old patterns. The repair is to remove the affected tiles, then remove the old thin-set mastic, being careful not to disturb the surrounding tiles, reapply new mastic and then re-set the tiles. Allow them to set overnight, undisturbed and the next day re-grout the cracks. If you don't feel comfortable doing the repairs or if it's not your building, either get your landlord involved or hire a flooring guy yourself.
