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Discuss Commissioning UFH, cracked screed, large tiles, help in the Underfloor Heating Forum area at

  1. WhattheScreed

    WhattheScreed New to


    I'd appreciate it if you guys could help me out here; I've been reading as many threads as I could on the matter over the last few days here and while I think I have a fair understanding of things, I'd like to provide the specifics of my situation.

    I have a 68 sqm apartment in which UFH (Uponor) was laid down on a 30mm thick polystyrene layer (below it is the concrete slab).

    On top of this, there is about 70mm of cement & sand screed (no clue about the brand). I was told by the builder that the screed is "reinforced with glass fibers". Moreover, the plumbing company that installed my UFH provided the builder with some Uponor-branded flexible screed additive that I am told was used.

    The screed was laid down in October and, from what I can tell, has had time to dry. There are some artificial joints (although the individual areas sometimes exceed the 15sqm figure I read around here), and there is also a perimeter joint. I can't say what was used to allow for expansion but it is a soft blue sort of spongy foam.

    As I said, the screed appears dry, and only one crack has appeared (a hairline crack about 30cm in length, starting from one of the joints). The screen is not level (the joint areas are considerably higher than the sides of the room), and my tilers have said that we will need to pour a self-leveling compound before we can lay down the tiles.

    The UFH has not yet been commissioned (it is powered by the central heating and the building isn't yet hooked up to gas).

    I plan on tiling with 10.5mm thick, 900x900 porcelain tiles everywhere.

    The tilers in my country are not at all well-versed in UFH, nor are they very keen on reading instructions or doing research, but maybe I do not give them enough credit. So, please help me out with a few answers.

    1) Am I correct in understanding that, even in my circumstances, I *must* commission the UFH prior to tiling? And that I should do so by ramping it up gradually to maximum, letting it sit there for 4-5 days, and then ramping it down?

    2) What should I do about the existing screed crack (and/or any others that may appear post-commissioning)?

    3) Should I commission before or after the self-leveling screed is poured down? Will that not also risk cracking?

    4) What should I use to allow the tiles themselves to expand? Are grout lines (3mm) not enough for the job?

    My tilers basically insist that my screed is dry and strong and has the flexible additive mixed in, and because of that and the fact that the tiles are "very strong" (the maker is Casalgrande Padana) I won't have any cracking issues if we simply lay down flexible adhesive onto the self-leveling screed and lay down the tiles.

    Thanks for reading!
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