Dave

hi jeff use sharp sand and cement..mix with about 30% water so its quiet dry in consistency but with enough moisture to set...use a straight edge to screed with....
An easy way is to use copper tube in long lengths and set at the desired screed height..just set them in screed...then put screed down spread about taking care not to knock the poles..then screed back with straight edge on top of the poles. this will give you a nice flat floor..once set remove poles and infill the channels with screed using your float....for fast track tiling use a green screed adhesive........hope this is clear enough for you to understand....its a similar method to what block pavers use when screeding there sand beds for blocking..............dave..