My first posting; I would like to thank all of the professionals and remodellers out there whose advice and pictures I have been gorging myself on. I have an urgent question as I just took a good look at the work on our bathroom project on my contractor's day off. He has installed 12 X 12 porcelain tiles in a small (5X8) bathroom in a plain square pattern; not grouted yet but at the corners where four tiles meet they seem to be out of whack and not level; I check with a level and the whole floor is not level. He specifically asked for 12" tiles not 18" because it would be easier to install. I was concerned when he said that he back butters each tile as he installs rather than puts all thinset down first; is this what has created the problem? Is this to be expected, or should a finished tile floor be level?? Should I insist this be redone? My house was built in 1988; not well I might add.