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UFH - Screed and Strip edge

Discussion in 'Plumbing and Central Heating' started by bassmonster, 20 Mar 2016.

  1. bassmonster

    bassmonster

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    Hi all,
    Looking for some advice please.

    I have just built a new kitchen extension which is just under 20 sqm.

    The ground level is quite low so we have 100mm of compacted gravel sand etc, damp proof membrane, Then 100mm celotex insulation. Followed by 100mm screed then another layer of damp proof membrane After we have another 100mm celotex insulation and under floor heating pipes clipped onto the boards.
    The floor has just had its final layer of screed on it of 65mm couple of days ago.

    However, I have only realised that we have forgotten to stick the perimeter edge insulation on the walls. Is this a big problem? What adverse affect will it have? Rather worried about this.

    Also, I have been reading about the drying times of screed. There is a lot of information to take in but it seems the general consensus is to allow at least couple of months before commissioning the ufh. I would like to know how long we should wait until we can start to tile?

    The screed mix is standard 1 part cement and 4 part sand. I believe the builder added something to make the drying process quicker.

    I have installed a radiator in the extension. Will this aid in helping dry the screed?

    Out curiosity, what would happen if ufh was turned on to dry the screed?

    Any info would be much appreciated.
    Thank you.
     
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  3. Dan Robinson

    Dan Robinson

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    Crack city. With a fair bit of heave. Sounds like a total cock up.
     
  4. bassmonster

    bassmonster

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    Do you mean the floor cracking?
     
  5. muggles

    muggles

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    Yes, the edge insulation is there to take up expansion and movement as the floor heats and cools. Without it, the floor will either buckle and crack, or start to push your walls out. Your screed supplier (if you've used a proper screed rather than just sand and cement) will be able to advise drying times and when you can lay tiles, but a month or two is not uncommon. Turning the heating on too early will certainly lead to the screed breaking up
     
  6. bassmonster

    bassmonster

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    Thank you for your reply Muggles.
    See as the screed is very soft still, will it be ok of we cut into the sides of the screed where it meets the wall and insert the insulation edge?
     
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  8. dilalio

    dilalio

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    Yes! It will be messy but, if you can, you should! It's not a big deal to rescreed the edges and your mind will be at rest ;)
    On UFH installs, we start to put heat in at a very low setting several days after the screed has gone down and step it up gradually over following weeks.
     
  9. muggles

    muggles

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    Yep, a 9" angle grinder held tight to the wall should do it (assuming nobody has been stupid enough to lay pipes tight to the wall). Then push the insulation down and glue it into place if you can. Once the glue's set you can trim it
     
  10. Agile

    Agile

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    That seems a rather strong mix for the final layer.

    I am also surprised at having two DPCs and would expect that to perhaps trap moisture unless the lower level was given a very long time to dry.

    Certainly retrofit the edge insulation!

    It is normal to wait a few days for the screed to become hard and then run the UFH from ambient ( say 20 C or less if there is no other heating ) and increase it by about 1 C every day. But that requires a system which is capable of fine control of the temperature.

    That will speed the curing of the cement and its drying.

    Tony
     
  11. bassmonster

    bassmonster

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    OK, it took me about 45 minutes to get the edges.... All done now... Just need to fillfill.

    Thank you for all your helpful replies.
     
  12. DIYnot Local

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