Under Floor Heating - Screed between joists

[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!!.

 

[corgiman]

Gawd only knows I am a plumber not a plasterer/builder

 

[chrishutt]

You say "between joists" suggesting that this is a timber suspended floor, in which case you won't be using a cement screed. The technique for UFH in timber suspended floors is different - check the web sites of the system suppliers.