Cemfloor - Hygrometer readings variation

Discussion in 'Subfloor Preparation' started by Aslan, Sep 21, 2021.

  1. Aslan

    Aslan New Member

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    Hello, looking for some advice on Cemfloor which was recently laid in our extension. I'm hoping there may be someone on the forum with greater knowledge of this product than the screed company that laid it, and our normal floor fitters are unfamiliar with it.

    For background, it's a block and beam floor, with plastic barrier on top, then 100mm insulation, another plastic membrane and then about 80-85mm of cemfloor liquid screed, no UFH, in a south facing extension with sliding doors that are frequently open to help ventilate. The screed went in 11 weeks ago, remains a bit dusty and slightly soft layer along one edge where we think there was some excess water. It's also about 10mm lower than the existing floor, so will need latex to try and level and smooth with existing floor. The screed company only provided a data sheet through our builder, which is similar information to their website stating it should be dry enough for LVT etc after 28 days for a 50mm floor, and that there should be no latence and no prep work needed.

    The floor company have come in, put a F-ball hygrometer in the centre of the floor and it's giving readings between 45% and 95% after 7 days down, depending on time of day, whether the sun its out etc. That variation makes no sense to me. We need a consistent reading below 75% for the latex to go down before LVT. The floor company say that due to the high readings, it will need a DPM before latex can go down.

    My problem is that I don't understand the variation in readings, for a floor that in theory should be well on it's way to drying. Even with a formula of 1mm a day for the first 40mm, and 2 mm a day for the remaining 40mm, that would give 120 days and we are already at 80 days. Surely a reading of 95% is not possible or reliable, if it is also reading 45% in the middle of the day in the sun?

    I'm not looking to rush it, I want it done correctly but nobody seems to know how long it needs or why those readings vary. Could it be that the cemfloor needs a sand to enable it to dry properly? could the hygrometer have been incorrectly set up? is 120 days about right for drying time to 75%?

    Any help would be welcome.
     
  2. Aslan

    Aslan New Member

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    Just to clarify, the hygrometer readings were taken last week once it had been down for 7 days (11 weeks after the screed went in).
     
  3. merit

    merit Well-Known Member

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    Hygrometers are a waste of time on those screeds. They are like a sponge and react to everything around them. As usual the screeding company don’t know anything about the products they are installing. Sounds like it needs more work doing to it. How has it ended up 10mm lower. Surely they can’t get it wrong with a liquid screed! I wouldn’t trust the screeders or the rate it’s meant to dry out. Better off just putting down a dpm.


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  4. Aslan

    Aslan New Member

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    Yes you would think it's impossible to get 10mm out with a liquid screed, but here we are... I think we are likely to have to put a dpm down as we cannot get a reliable answer on whether it is dry enough or not, and we can't take a chance. But I don't want that put down if it still needs sanding or other prep first.
     
  5. Rugmunching

    Rugmunching Well-Known Member

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    I'd still be giving it a good grind/sand down then going the epoxy DPM route
     
  6. Distinctive Adam

    Distinctive Adam Well-Known Member

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    As above
     
  7. J d clarkson flooring

    J d clarkson flooring Well-Known Member

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    Remove any laitence so you can see the aggregate and is dense and solid…. Then use an epoxy dpm to be safe.
    Builders say these are fast drying but dry the same as traditional screeds unless incorporating ufh based on experience.
    Your floorlayer will know the best route.
    Just done one and pre smoothed with latex screws then epoxy dpm and top coat of latex.
    Make sure the latex is moisture tolerant and so is the primer
     
  8. LKAB Gypsol Alan Jackson

    LKAB Gypsol Alan Jackson Well-Known Member

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    The flooring company are not using the hygrometer correctly if it's been on the floor for 7 days. As for the screeder they should be able to supply you with data sheets.
     

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