Uplifting Tiles

Moisture causes a variety of unwanted effects beneath tile, culminating in a compromised substrate-tile bond — the substrate is the tile installation surface. Moisture may be coming up through your home's concrete slab, causing the tiles to lift up, or loose tile may indicate an unseen plumbing leak inside a wall.

Don't ever lay tile without grout, the tile will prematurely crack and chip rubbing against each other. It might rub together if laid on a wooden floor/subfloor since movement is possible, his basement has a concrete floor and thus no movement. Thin set mortar will hold it tight enough it would not move and chip.

Hollow sounding tile is not a defect per industry standards. If there is no resultant damages to the tile or grout, then I would just let it go. Make sure you have extra tile for the future just in case they do get damaged you can replace them.

If the cracking is a result of issues such as a cracked subfloor, incorrectly spaced joists, or protruding screw heads, these will have to be dealt with in addition to the cracked tile. Natural causes. Natural circumstances such as moisture penetration, pressure changes, or aging can also cause cracks.