I was on an inspection yesterday that included a delaminated tumbled marble floor tile installation. How did I know that the floor tile had delaminated? I sounded the floor with a length of chain which identifies hollow resonance in tile that may be delaminated. The real test comes from striking the tiles with the butt of a margin trowel and feeling for vibration within the tile body. Hollow sound coupled with vibration indicates a delamination. The tile is then removed from the substrate to prove the theory. In this case, an improper sized trowel was used to lamainate the membrane to the concrete slab resulting in an insufficient setting bed to hold the membrane to the slab. The result was a delamination between the membrane and the slab. Hence hollow, delaminated, and moving tiles complete with fractures in the tile bodies and grout joints. My advice, follow the manufacturer's recommedations precisely!