Hi Everyone, I'm new here and was really hoping for some professional advice. I bought a new build 21 months ago. Within a couple of months we noticed hollow tiles that knocked and tapped when walked on. After 18 months the builder finally agreed to redo a number of the tiles for us as a gesture of goodwill. The tiles themselves Marazzi Treverkever 20x120 cm came up in one or two pieces and were totally clean on the back of the tile. The Adhesive left on the floor was so brittle and crumbly I could remove much of it with my fingers. We have had recommendations to go to TTA but we simply cannot afford it for the area we would need looked at. The builder is adamant there wasn't a fault with the floor even thought the tilers on site admitted they believe it wasn't primed. Not all of the floor has been done and I am now concerned about those areas left. I have attached a couple of photos that show the tiles came up clean for reference. Would really appreciate any tips/advice/pointers I have no idea where to go from here when the builders are refusing to admit there was a problem. Thank you in advance!