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