Self levelling screed cracking with wet UFH

Discussion in 'General Flooring Chat' started by Ollie20964, Sep 1, 2019.

  1. Ollie20964

    Ollie20964 Member

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    Hi,

    1st post for me but desperately after some advice as to why my self levelling screed is cracking.
    Background:
    I am currently renovating a 1950’s property with no DPM.
    The first thing I did was remove the old parquet flooring and take up the old thin screed (15mm). I then poured a liquid DPM over the slab (Ardex DPM) followed by a thin layer of Ardex NA (within 48 hrs) as per manufacturers instructions. Two weeks later I primed the NA and started installing Uponor Minitec system. (A low profile wet UFH with 15mm height build up). I stuck the plastic egg crate panels down and fed all the piping in as per instructions.

    Next up was pouring the self levelling. I used CTD’s Ultra Trade One Deep fill floor leveller which it said was suitable for underfloor heating.

    I mixed it as per the instructions using their mixing buckets, correct ratio etc. I poured it to approx 18mm deep
    Within a few days of it drying (prior to turning on the UFH I noticed hairline cracks appearing. These started getting worse but it still felt solid. A week or so later I turned on the UFH as low as it could be 20 degrees. I gradually increased with one degree a day but as I did so the cracks got worse and worse so by the end the whole flooring had hairline cracks running through it (approx 1-2mm thick). It still felt solid though.

    I got a professional floor layer in and he couldn’t work out why it had done it but suggested I would have been better of using a reinforced one which had fibres in it however as the one I used was supposed to be suitable for UFH he said it should have been fine. He suggested filling the cracks with Ardex feather finish (which he did). After this he primed it again with F.Ball and poured F.Ball latex floor leveller on top (approx 3mm deep) to ensure it was perfectly smooth as I am having LVT put ok top.

    I didn’t put the UFH on and left it a good few weeks to ensure it’s properly dry. I then noticed one hairline crack appear. I decided to put the UFH on and have now got it up to 30 degrees. Now i have seen all the hairline cracks are coming back again. It still feels solid but my worry is they are getting worse. Will they eventually get so bad it starts breaking up? I just can’t work out why it is doing it? I did break up a small part in the corner and tested it for damp / trapped moisture but it is dry as a bone?

    I did phone the manufacturer of the floor leveller and they said that it is because I am putting it on top of Ardex NA and NA is a softer compound and there’s is a harder which is why it’s cracking. The NA was feather finished though and I had to put that down on top of the Ardex DPM as per the DPM’s instructions. I said this to the professional floor leveller and he said what they said was a load of rubbish. He is at a loss why it’s done it.

    I will attach some pics for reference of the worse cracks.

    Any advice would be much appreciated!!
     

    Attached Files:

  2. dazlight

    dazlight Super Moderator

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    You didn’t need to put the ardex NA down.
    That is a softer screeding compound so you shouldn’t of put a higher compression screed onto it so that can cause cracking.
    Also putting that screed down at 18mm in one hit is to thick going above a dpm. Would of been better doing 3 hits of 6mm.

    A fibre screed is always a better choice as that has more flex to it in case of any movement.
     
  3. dazlight

    dazlight Super Moderator

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    Which f ball screed has he put ontop ?
     
  4. merit

    merit Well-Known Member

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    Should of just kept with NA through out the job


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  5. mickyr2

    mickyr2 Active Member

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    Should of put na down first then dpn then na back on top seen this many a time done when its failed

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  6. Spacey

    Spacey Super Moderator Staff Member

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    Yep NA is to soft and when you do two layers of screed they must be the same compression strength and the top layer must not be thicker than the bottom
     
  7. Paul webb

    Paul webb Well-Known Member

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    I just put the first layer of screed on a similar system on Friday, i used a fibre reinforced screed which hopefully should be more tolerant of the expansion and contraction of the plastic pipes and doing it in two coats, due to the depth of the empty troughs, when the manufacturer states suitable for ufh, they may mean for on top of the finished slab and not for setting the pipes in
     
  8. Spacey

    Spacey Super Moderator Staff Member

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    The screed must be suitable to encapsulate UFH and able to be used at a suitable depth
     
  9. Distinctive Adam

    Distinctive Adam Well-Known Member

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    The ultra will have to be ripped up before it eventually fails, never mix different manufactures, stick to a system, almost any screed is suitable for use with UFH, just use it correctly, there’s some there are Pacifically designed for ufh but not so well known in the U.K. meaning you can go 5-6mm above the system rather than 10-12mm.
     
  10. Ollie20964

    Ollie20964 Member

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    Many thanks for all the replies. So it looks like it’s crackinf for multiple reasons, not being compatible with NA and not suitable to encapsulate the UFH pipes. I had no choice with the NA according to the spec sheet of the DPM, I had to put a thin layer of NA over the top. I guess I should have used a softer fibre reinforced screed poured over the top then.

    My next question is has anyone got any ideas as to what is likely to happen and is there a remedy? It hasn’t completely failed yet as although there are cracks when you tap it it all still feels solid. The small area I broke up it seemed well stuck to the castellated panels as well. That said there does appear to be more of these fine cracks appearing and the screed has been down since mine June.

    Is this likely to keep cracking and then eventually break up or will the panels keep it held together?

    Thanks again
     
  11. Ollie20964

    Ollie20964 Member

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    Sorry, to clarify the ultra is only a few mm above the system. Total build up (including the castellated panels housing the UFH) is 18mm. The ultra is a deep fill which says suitable up to 60mm in depth
     
  12. Ollie20964

    Ollie20964 Member

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    Not entirely sure, I know it was a smoothing one that was reinforced. He said I would have been better off using a reinforced one which I used for the pour on the castellated panels
     
  13. pf flooring

    pf flooring Well-Known Member

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    Ideal world take the screed up and start again, realistically speaking although very wrong and will probably still have an issue down the line feather finish the lot and hope for the best with no guarantee, really you should start again but it's your home at end of the day and your money.

    I did a plastic tray ufh job that had cracks in it as builder had not done it right, we sanded it all back to get a good key then primed and flex screed over it, 12/18 months later and it's fine but that was done with the builder signing a legal document saying if it failed he was libel for the full replacement.
     
  14. Ollie20964

    Ollie20964 Member

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    Thanks. What screed did you use?
    I really don’t know what to do at the moment. Because the screed seems solid and well stuck down at the moment (from the bit I broke out) it’s going to be a pig to get up, plus it’ll probably damage the liquid DPM I put down and be a nightmare to get it flat again so I can re-stick new panels down (without building up the floor height even more). Part of me thinks do I leave it and wait for it to fail? Hoping there is a chance that it doesn’t. It’s quite a bit of money to write off and then do it all over again. Has anyone used Mapei Eporip? It seems to be an adhesive that can bond cracks in screeds?
     
  15. mickyr2

    mickyr2 Active Member

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    Best thing to do is phone the ardex rep up get advice off him if it fails again it will be under warranty of them as they have advised you it's common sense really

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  16. Spacey

    Spacey Super Moderator Staff Member

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    You could prime, lay crack repair mesh over the whole lot then screed Again with NA or a firber reinforced screed
     
  17. Rugmunching

    Rugmunching Well-Known Member

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    If more cracks are appearing then how worse will it get...

    Either start over (which I dont think you are feeling) or mesh it, flood it with some fibre reinforced screed and hope for the best.
     
  18. Ollie20964

    Ollie20964 Member

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    Hi, it’s more the cost of having to redo it that’s the bitter pill to swallow as the pipework, panels, DPM will all need doing plus it will a very hard to get up. I’ll also have to break up quite a large section of the hallway as well as the pipes run out there to the manifold.

    I guess the mesh crack repair I’ll need to put a fair amount of self levelling down on top? And then if the stuff underneath does eventually fail the stuff on top will fail as well won’t it?
     
  19. Spacey

    Spacey Super Moderator Staff Member

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    [QUOTE="Ollie20964, post: 128806, member:

    I guess the mesh crack repair I’ll need to put a fair amount of self levelling down on top? And then if the stuff underneath does eventually fail the stuff on top will fail as well won’t it?[/QUOTE]


    Nope and no it shouldn't
    https://www.uzin.com/product/direct/256-uzin-reinforcement-webbing/
     
  20. dazlight

    dazlight Super Moderator

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    Lay Quickstep Impressive Laminate over it. I wouldn’t be gluing to it.
     

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