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Hi guys,

I'm having some trouble with my builder and the plumber who fitted my underfloor heating. In a nutshell, the plumber has laid Hetta aluminium pipes over c. 40 square metres comprising of two zones. The builder has then laid around 6cm of semi dry aggregate-based fibre screed. He's then added self level compound on top. The only thing left to lay is karndean vinyl floor.

The problems I have identified to date are as follows :-

1. The water pipes were not hot when the screed was laid so I am worried that when they heat and expand, it will crack the screed. (I'm not sure whether this was the plumber or builders responsibility)

2. No insulation was applied around the edging of the screed so I guess there's a risk of cracking either within the screed or the wall plaster (again not sure if this was builder or plumbers responsibility)

3. The self level compound that's been applied was 10 bags of Palace compound mixed with 4 bottles of Febflor latex and 6 part water. (I'm not so worried about this given it's only about 2-3mm in depth).

particularly on the first point, it would be great to know what others recommend I do now? It's been about 3 weeks since the screed was laid so I believe it's too early for my to switch the heating on. I've got to make a call on whether I either :-

a) Crack on with laying the vinyl floor and fitting the kitchen and hope for the best


b) dig it all back out and do it again. This will cost c. £500 for the screed and another £1500 for the underfloor heating (presuming the pipes can't be saved).

Would welcome all opinions.





Staff member
S. Mod
Gas Engineer
Don’t need the heating on when you lay the screed but do need the pipes to be full of water and upto spec

this should be ok not the best or correct way but should be fine

normally 2L of water per bag but may differ consult manufacturers instructions
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Advent Win
Definitely no heat on whilst screeding. But should have been pressure tested to manufacturers requirement then left at a couple of bar whilst screeding. Slight pressure increase as the concrete goes in and heats up.
Plumbers issue, but builder would have had to let him know when he was screeding.

Edging insulation more to stop heat bleeding into the building structure.

Personally I would warm the floor very gradually in line with the requirements of the screed prior to laying the vinyl flooring. Also the same with the self leveller but that's just me. But I would be annoyed at the new screed needing a self levelling compound.


Gas Engineer
As said above, it isn't the ideal install but should be OK. My only other concern would be normally there is a foam edging strip placed around the perimeter of the room to absorb the expansion of the screed slab when it is hot, I believe it helps avoid cracking. Not sure how vital it is, may be worth asking a UFH company and see what they say.

king of pipes

Gas Engineer
Advent Win
As above not ideal the slab will expand and contract and it really should have perimeter insulation , pipework should of been pressure tested and left pressured up whilst screeding , I would warm the slab if possible over a week if you have floor stats this will be simple to do starting a couple of degree increase each day a long slow warming is better than a thermal shock which could possibly cause cracking , I wouldn't be laying any floor coverings until you're confident the floor is sound and the Ufh hold pressure. Kop

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