Poured depth for screed top on underfloor heating?

[Mike2007]

We aren't going to use loose sand and cement screed because we aren't builders.
So we need a poured top to our underfloor heating circuit. The original plan was anhydrite to give thin finish, but nobody local does it.

What is the minimum depth for a cement based poured screed?

 

[muggles]

Depends on the mix but around 50mm as a minimum