"Floor screed mix should be fairly dry" ?

[Darren1234]

I've read a lot of sites and discussion all pointing to floor screeding being a fairly dry mix (4:1). Squeezed in the hand it should retain its shape etc.
None of what I've read discusses what happens if you make it too wet?

I'm putting a 70mm 4:1 sharp sand screed over water under floor heating pipes (with a mesh on top) and was thinking of making it a wetter mix to make sure it flows as best as possible around the pipe work and below/through the mesh as best as possible.

Will it have an adverse effect making it too wet?

 

[^woody^]

All the water will float to the top, pond, and you wont be able to trowel it flat.

It will basically turn in to a right mess

 

[r896neo]

You can get pumped flowable self levelling screeds for this very purpose but they are not a diy option as far as i know?

But there is no middle ground between those and a conventional semi-dry screed.

 

[mointainwalker]

When I screeded my floor and the UFH pipes I laid a wetter mix to about the level of the pipes and then a drier mix on top immediately afterwards. The object was to do what the OP wants i.e. best coverage/contact with the pipes.

 

[noseall]

The problem with a wetter mix below means that the surface will still be able to wander around and 'float' on the wetter mix.

There is much effort and labour placed into working the dry screed so the last thing you want is it to float about as soon as you try and float-rub it and trowel finish the surface.

r896eno gave the best answer.

Either use a proprietary wet screed or use dry. Don't try and lay a hybrid it will be difficult to work. However, if you are not doing it professionally, i.e. have plenty of time, then it may be possible to lay some wet stuff, allow it to dry up then continue with the dry topping later on. This must be done the same day to avoid delamination of the screed material.

 

[Darren1234]

Thanks all, its done now thank god. 16m2 of 70mm screed by myself has took nearly all day and I'm knackered

I tried an initial wetish mix (it didn't self float by any means but was easy to tamp down into the mesh and pipes) and very roughly floated the top.
By the time I got to the 3rd mix I had exaclty what you said, the top was puddling and I had to force the water to the edge of the screed to get rid of it.
I then tried much drier mixes which you could still successfully push into the grid/pipes but it took a lot more work. There's no way I would have enough time ( or energy for that matter ! ) to do that all day so I found a happy medium between the two. I could reasonably work it into the job without it puddling too much. only when I tamped down with my batton did I get any real water and then only a little.

It's a conservatory floor I'm doing and it will be tiled so the finish doesn't have to professionally perfect .

My only concern now is the fact that the pipe is primed with water and I hope there isn't too much of a cold spell before I get the rest of the job done. I'm thinking of filling it with Fernox or something to act as an antifreeze. Thoughts?