Which sand for UFH biscuit mix?

[davejaydj]

I have been googling this question and although many people have asked the discussion always seems to go off at a tangent!

I am laying UFH pipes between joists on top of 50mm celotex and will top with 20mm biscuit mix - dry sand & cement @ 8:1

I have over-ordered and have a bulk bag of builders sand left. Can I use that or should it be sharp sand?

 

[Agile]

I would say that it should be soft ( builders ) sand.

But just based on my personal experience and I cannot give any technical reasons!

Tonby

 

[ree]

As above. Use the bulk bag. Believe me, we use whatever sand is at hand on site. No way will the job stop while we get picky. Most sands work in most mixes for most purposes - no call backs yet.

 

[davejaydj]

Thanks for the comments. In the end I decided to a mix - 4 sharp, 4 soft and 1 cement. Have finished the top floor and can't finish the UFH to the kitchen as around 150 bags of Monocouche render are stacked there! Soft sand gone now, so I will see what's around when I can get to finish the job!

 

[Pooley442]

Can I ask if the mix is going to be incased between PIR and floor boards, why add cement? Would just a sand mix not suffice??