I had a ceramic tile floor fitted onto concrete in my kitchen about 12 years ago. They have just started bulge - as though they are under some sort of pressure. Around 12 are no longer attached to the floor and bulging upwards. The grout is starting to crack. I've removed a small tile and the adhesive is attached to the tile and not the floor. The floor seems to be sound, flat and dry. What could the problem be? Any ideas?