UFH + Screed + Drying times + sealing

Discussion in 'Tilers' Talk' started by digga, Jul 19, 2018.

  1. digga

    digga New Member

    I hope someone can help, I have had a new living room built, wet UFH pipes laid on top of insulation and a DPM. The UFH was pumped to 5 bar prior to screed pour . A 70mm ish sharp sand+cement+fibre mix screed layer was recently laid.

    I want to install Karndean flooring in this room, ideally ASAP.
    I have been scouring the internet and there appears to be lots of articles and post and alot conflict. Can someone with experience please help answer the following.

    1.) Initial dry period :
    A) should we wait 5 days before opening any doors and or windows, to aid strengthening of the mix?
    B) Should the floor have plastic or sprinkled small amounts of water for the first few days to aid curing. Does this make much difference?

    2.) Curing: I read this should dry at approx 1mm per day. (i.e 2 months)
    Should all windows and doors be open (in this lovely weather) to help aid drying times? Or could this affect the strength?

    3.) UFH :
    Should the UFH be left off completely until dry, or should the UFH be put on minimum temperature (With 1 degree added per day) after a month or two to help aid drying?

    4.) Sealing:
    The contractor stated he usually lays Unibond sealer on to the screed to prevent damage from foot traffic.
    a) Is it worth doing ? - Will this affect drying times? - This room will be out of bounds
    b) Will this affect Karndean adhesives, or any prep for the flooring?

    5.) Karndean
    A) A floor stated you can lay a DPM and top level screed after getting to 75% humidity, will this cause any issues ? I.e how does the screed continue to dry if it's been sealed off? Will it affect the UFH etc.

    Thank you.
  2. rogerk101

    rogerk101 Well-Known Member

    Your UFCH pipes should remain under pressure for a minimum of 28 days. (Everything I've ever read says 6 bars, but 5 bars is probably OK.)
    There are two things to consider:
    1. screed setting time: 28 days (see above) - only important for when you can start heating, i.e. don't run any heat through the pipes during these first 28 days
    2. screed drying time: The only entity that cares about the moisture level of the screed is what you're laying on it.
    • If you're laying tiles, neither the tiles nor the adhesive cares about the moisture level of the screed, so you could start tiling a few days after the screed was put down ... it should have set sufficiently to have stopped moving by then. If it's UFCH, you'd be using slow set flexible adhesive anyway, so you should be fine.
    • If you're laying wood without a vapour barrier, then you would want the moisture levels of the screed and the wood to be roughly the same before laying. Only a moisture meter could tell you that.
    • If you're laying wood with a vapour barrier, then moisture levels can differ, but not enormously (In this weather, with windows open whenever possible, 28 days should be fine.)
    • I don't know what Kardean is, but its instructions should clarify.
    digga likes this.

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