Plumbers advice for underfloor heating and screed

[Steve Wegerle]

Hi guys,

I'm hoping to get some professional opinion on how my builder has gone about my extension and particularly screeding over the underfloor.

The project is to take a room which was originally 7m by 3m and extend it out 7m x 5m, and fitting underfloor heating throughout. The original space had a concrete block and beam based floor, the new extension has been made up by pure concrete. To prepare the floor for underfloor heating, he dug the original floor down to the concrete block and beam and then laid celotex insulation across the whole space. The original area came out slightly higher than the new extension. I then had a professional plumber come in to lay aluminium underfloor heating pipes. My builder has then laid a thick layer of screed on top. It's about 5cm over the original floor 7-8cm over the new area.

Up to here, I'm reasonably comfortable with what he's done although I think the screed on the new area is a little thick. He's then gone and got himself 10 x 20KG bags of Palace self level compound and mixed it with 4 x 5L of 709 Febflor Latex Plus (and presumably some water). This concerns me because :-

1) I believe this latex is for timber floors

and

2) It's the wrong quantities of latex to compound. I understand latex is important when laying over underfloor heating but im not sure why (I guess it's either heat conduction or maintaining its integrity when heated).

I am also concerned that the height is creeping up and up.

I will challenge him on his approach to all of this and I am sure he will play down that there is any issue so would really appreciate some input into whether I have cause for concern or not?

I've attached a couple of pictures before and after the original screed getting laid.

Thanks,

Steve

 

[Notch7]

Palace self level
PALACE SELF-LEVEL is a protein free cement-based, sub-floor smoothing underlayment that has been formulated to provide a consistently level finish to solid sub-floors prior to laying ceramic or decorative floor coverings, giving a consistently level screed from a 2mm up to 12mm thick

https://palacechemicals.co.uk/shop/flooring-range/self-level-floor-leveller/


709 FebFlor Latex Plus is a premium rubber based latex additive for use with Self Level Floor Compound and powder tile adhesives to both strengthen the mix and provide a limited degree of movement capability in the sub floor. Ideal for use when covering sound timber flooring substrates to allow for limited amount of movement
https://www.everbuild.co.uk/product/709febflorlatexplus/


I don't think it matters whether the substrate is timber or not, it's an additive designed to allow a bit of substrate movement.

Whether the 2 products are compatible or not, I imagine you would need to ring their tech dept to find out.

 

[Notch7]

Your builder should have lowered the inner skin of brickwork across the opening and run the insulation and screed across to the outer skin.

As it is either there will need to be a threshold across or if tiled over the bricks there's a risk of the tiles cracking.

 

[Steve Wegerle]

Thanks for the reply. I will try the tech departments of both companies but I would have thought they wont know each others products to comment.

Yes I see your point on taking the screed layer above the inner layer of brick. I've today had bi-folds fitted along the outer layer. The plan is then to have karndean vinyl floor tiles laid over the whole floor (including inner layer of brickwork). Hopefully because its vinyl, there's no risk of any damage to the finished floor.

Should I be concerned at all about the low quantity of latex comprising the self level compound?