Have spent hours trying to make a similar ceiling look good. Looked ok when i finished at 5! Next morning bright sunshine it looked ****e, needless to say client wasnt to pleased. Ended up skimming it anyway! client happy!
Sorry tony! Handyman is right,every house i have worked in has some form of damp course, otherwise they would all be damp.
There can be many causes of the damp as mentioned, try to pin point yourself before calling out an expensive firm.
sometimes there can be a lot of waste, generally a minimum of 10% can be a lot more with bigger tiles. He will have had to cut a lot of tiles thats where the time can be taken up. This is why I price for the job and not by sqm so as not to have any confusion. By the sounds of it you agreed...