Screed for under floor heating

[bozzle]

Hi,
I am installing wet underfloor heating and upstairs I have been advised to surround pipes in a 25ml bed of 8:1 sand cement dry mix screed with ply above and insulation below.

Am I correct in thinking dry mix should remain as a powder or should I be adding water so it sets.

If a powder does it matter if the sand is a bit damp

Any advice would be much appreciated as I am pretty confused!!.

 

[noseall]

when you say upstairs, do you mean the first floor of a house, which has timber floors?

 

[bozzle]

I am also putting in UFH downstairs but I am referring to the 1st floor bedrooms

 

[bozzle]

Forgot to say that 1st floor is conventional layout with timber joists and insulation, pipes and screed will be between joists with 18mm plywood as the new floor on top of the joists