Underfloor Heating & Screed

[deansewell]

Quick question. We are having warm-water underfloor heating installed to a 4m x 8m are. This is being fitted to an open plan kitchen / dining area, with a 120mm concrete slab (not reinforced), 120mm of insulation over, then 80mm screed.

My builder has fitted steel screed rails over the pipes to assist leveling. My question is is this ok for a screed floor with underfloor heating pipes installed? He has added insulation to the edges to allow for expansion, but I am concerned that metal rails / batons will restrict screed expansion as the floor warms, and may cause cracking.

Has anybody had any experience using metal screed leveling rails and underfloor heating? Any advice would be greatly appreciated.

Regards,

Dean

 

[cider]

Cant imagine it will cause problems but give your underfloor heating designer a call.

 

[Kev F]

done quite a bit of ufh and can honestly say ive never heard of doing that, can he not screed very well.

 

[JohnEBoca]

A competent floor screed layer would not need to use such rails.

If he intends removing them before completion, then I see no problem.

 

[deansewell]

OK. Now I am concerned...

I will call the UFH Company first thing tomorrow as suggested (Continental UFH), and see what they say. From looking at the rails, they are not going to be easy to remove as they are a C section, the bottom half if the C is set in a concrete strip over some of the UFH pipe.

I will see what the UFH company say, and maybe he will need to remove them (very, very carefully so as not to damage the pipes).

Screed being delivered tomorrow!

Any further advice or experience REALLY welcome!

Thanks ALL,

 

[deansewell]

Having just checked, the "rails" are actually Dryliner Channel (galvanised steel)

My concerns are two fold:

1) This is an 8m x 4m area. Is it best practice (or even regulation) to include an expansion joint, thus making two 4m x 4m areas? (Currently the channel runs the full 8m length)

2) concern that the screed will crack due to continuous expansion and contraction due to the underfloor heating. However, I do recall that steel and concrete have a similar expansion coefficient of thermal, so maybe not a great issue!

Please help and advise!!! Screed is being delivered tomorrow, and I have no idea if this is a good design, but doesn't feel like best practice to me

Thanks.

 

[Kev F]

basically i would not lay any screed until the bars are taken out. The expansion areas will sometimes be decided by the manufacturers spec but normally an expansion edging round the walls is enough. I would call off the screed for the morning

 

[Norcon]

Leveling screeds are not normally used in small areas like these.
Most flooring contractors will form a screed with the screed material up one side of the room using a straight edge then the other side and then turn 90 degrees for the center.
On larger projects a laser level is useful. In some instances the receiver can be connected to the rake shaft that the operative is using thus allowing him/her to check the level at various points with a vibrating libellula following behind.

 

[Peterade]

Golly Deansewell,

What happened? Did they cut the metal. Did it work out okay?
You can't just leave us all in the lurch!