My screed floor looks flat, but its certainly not.

Comparing the high and low points, there is upto 10mm difference in
height.

I was originally going to put some self leveling down, but my
neighbour (who is a tiler) talked me out of it. Instead, he said that
I could vary the thickness of the adhesive to level the floor.

Is this suggestion OK? If so, whats the maximum thickness of adhesive
that I can lay?

Jon