hi Jamieogh, I'm empathise with u. I had 2 frens who did cement-screed, one did for his whole living, dining & kitchen area (industrial look), the other one cement-screed his bathroom & balcony area. The 1st one had same problems as you, in fact before even the contractor handed back to him, there were already some cracks, so he made the guy re-do the whole thing! Of course contractor not happy..but can't help it. So after hand-over, within 2 months cracks appeared over a few areas. He made the contractor came back to re-do and pay for his hotel stay. The 2nd fren didnt have this problem. When we chat with his contractor, he said its the level of water in the mixture as well as whether they had properly let the cement dried up in earlier layer. So if contractor rushed and the cement not dried properly, so when it dries up, the cracks appear due to the tension. Hope this help u to understand why. ;-)