I have recently had a a conservatory built. The floor was laid in two stages as they ran out of cement. They laid polystyrene and put the screed on top of this. The problem is that the gap between my interior doors threshold is only 15mm and I cannot lay the tiles I want. The floor is very powdery and I swept up 2 carrier bags of loose cement. It has also cracked in the last 6 weeks and moves slightly by my entrance door. I suspect that this is because they never excavated the path that ran alongside the front of my house. The builder insists that "The screed floor finish is generally approximately the same level as the internal to the house, and that as when a carpet is laid the doors from the house into the conservatory need to be adjusted!" I would be really grateful for any advise on all of these points please. Thanks John.