thinner alternative to flowing liquid screed - views?

[mikeysoft]

Hi All,

 

My first ever post on buildhub, after nearly two years of lurking and reading good information - thanks.

 

I'm renovating our new home before we move into it. Part of the rennovation is installing a retro-fit under floor heating system on all floors. For the ground floor (existing concrete slab, ~165m2) and first floor (new posi joists, ~140m2) I'm using 16mm PEX-AL-PEX pipe contained in Profix PLUS panels.

 

Like many on here, I've decided to use a flowing liquid screed to encapsulate the pipes, most probably Cemfloor Therm, which would result in an overall heated screed height of 50 to 55mm.

 

Today, I stumbled upon a possible alternative which, like most options, has advantages and disadvantages, depending upon what is import to you personally.

 

The product is Sikafloor 440 Level Fibre Reinforced. Other companies make similar products, which I'm sure some of you will have used. I'm quoting this one because Sika specifically state this one is "Designed for the embedment of underfloor heating elements", and even the image on the 20kg bag shows a picture of it being poured onto UFH pipes. It seems to be very strong ("strong enough to take light vehicular traffic") and the mimimum depth is 5mm (max 30mm for self-levelling in one application).

 

This product has the potential to give a much thinner screed replacement - 25 to 30mm in my case, instead of 50 to 55mm (for said flowing liquid screed). For arguments sake, let's assume Sika are correct and it won't crack at say 5 to 10mm over the pipe (I spoke to Daghan at Sika today and his preference would be 10mm over the pipe with it having less rigidity than say something solid, like concrete). Some people will have no interest in saving 20 to 25mm floor height, but I do because I'm retro-fitting, so eating into existing floor to ceiling space on two floors (then resilient channels for ceiling plasterboard, etc.).

 

Obviously this is a very different proposition to a screeding company applying a liquid screed in half a day - it would be a much heavier and more labour intensive job (but some people may prefer doing it themselves). Also, it may work out more expensive, depending upon the size of the job. I think both of these points are down to personal preference and priorities - my big concern is not these, but heating system performance.

 

I'm interested to hear views on the viability and behaviour of such a thin heated layer. Thermal mass - I'm guessing it would somewhat change the reaction times (quicker heating up, quicker cooling down). Are there any significant differences it would give in terms of the heating system behaviour? Once it's fully heated up, and is giving off heat... I can't think of much but I'm sure some of you can!

 

Sikafloor 440: https://gbr.sika.com/en/construction/flooring/sub-floors-cementitious-flooring/self-levelling-compounds/sikafloor-440-levelfibrereinforced.html

 

Cheers

Mike

Edited February 14 by mikeysoft
highlight my point

[nod]

Anything Sika is good 

I’ve use there self leveling regularly 

Your going to need 2 bags per m2 

Nearly 300 to mix and lay Seems a shit load of work to save an inch 

I’d leave the rez bar off if it was that crucial 

[Nickfromwales]

4 hours ago, mikeysoft said:

I'm interested to hear views on the viability and behaviour of such a thin heated layer. Thermal mass - I'm guessing it would somewhat change the reaction times (quicker heating up, quicker cooling down). Are there any significant differences it would give in terms of the heating system behaviour? Once it's fully heated up, and is giving off heat... I can't think of much but I'm sure some of you can!

If you are happy with caveats because you want a "thin" system, then just treat the floors like a very nice radiator. Simples.

 

You'll get heat relatively quickly when you need it, but suffer a very big hysteresis; unless you can get the flow temp dialled in very well and address the under-over shoot with a bloody good (~0.1-0.2^oC increment) thermostat. 

[Russell griffiths]

12 hours ago, nod said:

Anything Sika is good 

I’ve use there self leveling regularly 

Your going to need 2 bags per m2 

Nearly 300 to mix and lay Seems a shit load of work to save an inch 

I’d leave the rez bar off if it was that crucial 

I thought about the amount of bags needed and thought he would need 4 blokes to do this, two mixing and two laying. 
seems like a lot of hard work when you could just pump it in. 

[Mr Punter]

Are you planning any ground floor insulation or is the slab already properly insulated?

[nod]

7 hours ago, Russell griffiths said:

I thought about the amount of bags needed and thought he would need 4 blokes to do this, two mixing and two laying. 
seems like a lot of hard work when you could just pump it in. 

The problem will be keeping it flowing 

You would several mixing and have to split it into sections 

[Big Jimbo]

Probably just me, but I can see that going very wrong, and ending up anything but level.

[bmj1]

You can do cemfloor at 45mm and call it a day. 

 

There's a couple of different cemfloor products but pretty sure we went as thin as 45mm on ours.

[JoeBano]

I used Weber floor system in my hallway needed something that could take foot traffic in 3 hours. It’s 50mm thick I used Ritmo render machine, 22 bags in 30 mins. It was warms up very quick compared to my traditional floor screed (65mm) in my kitchen but that keeps the heat way longer. Bag screed costs 3x times more than traditional screed. 

[Harpham]

Cemfloor do a Level Plus Flowing Screed - 12-25mm above pipes.

 

We are hopefully having this on our first floor on top of Uponoor Minitec UFH pipes which are 10mm laid.