missing damp proof membrane

Discussion in 'Building' started by backupnorth, 30 Oct 2019.

  1. backupnorth

    backupnorth

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    when the floor slab was cast some of the polythene membrane disappeared into the concrete. when we had a lot of rain last week we had a puddle on the floor by the low level window. The builder has coated the inside of the floor and the thermalite blocks that weren't covered by the membrane with bitumen. Is this OK? My thought was that the bitumen will eventually dry and crack or that there might be some settlement and get cracks which will let more water in. Am I wrong?
     

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  3. bobasd

    bobasd

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    the usual order for a poured floor is roughly: first the DPM membrane then the insulation, and then the pour to about its benchmark height.
    the membrane is taken up the walls about 150mm above FFL height.

    you show one pic with no DPM.
    and the next pic with what appears to be DPM material going up the walls - or is that black "skirting" the bitumen you talk of?
    is that floor level waiting for another pour to bring it up to about FFL height?
    has the plaster been stopped high for that reason?
    i dont understand why bitumen has been painted on the floor?

    why not post photos showing the outside of the low level window, and the patio doors at ground level?
     
  4. ^woody^

    ^woody^

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    The problem with that surface coating is that what is most likely to happen is that the damp will still be getting in to the floor slab and could travel further along because the surface coating prevents it evaporating away, and it pops up where the coating ends.

    This will be longer term and will depend on the amount of continuous wet weather you get. So it could be fine for a while and then once the builder has long gone, you get that horrible mould smell and rotten carpets or squishy laminate.

    As this is a builders defect, either get him to correct it by taking up area of floor and sort the DPM out, or to coat all the floor with a proper surface coating (not a tin of £4.99 bitumen from wickes), and to seal what should have been the DPM/DPC junction.
     
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  5. backupnorth

    backupnorth

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    Bobasd the second photo shows where he has bitumined the "skirting". the floor is waiting for insulation and skim.

    woody, I am preferring your first option

    it rained again yesterday and water came through coating!

    Builder back in again and hopefully getting better fix.

    thanks for advice

    attached photo shows cast slab photos of outside to follow
     

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  6. backupnorth

    backupnorth

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    attached is outside view of low window, not many details as the patio has been put down
     

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  7. ^woody^

    ^woody^

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    Oh dear.

    Has the building inspector passed that, or just walked past it?
     
  8. backupnorth

    backupnorth

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    building inspector also didn't notice that the plates holding the two halves of the beam supporting the back wall of the house had 5 missing bolts and the uprights were not bolted to the floor or fixed back to the walls
     
  9. bobasd

    bobasd

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    OP, the patio is too high, its bridging the DPC in the outer skin - also, its presumably allowing moisture to creep under the low window frame.
    the render is also, presumably, bridging the outer skin DPC - plus it might be in ground contact.
    render should not touch the ground surface and should be finished with a Bell cast just above the outer skin DPC.

    i take it your outside walls were not built off the slab thats shown in the "cast slab" photo?
    and that wherever the membrane (DPM) has reached and gone up the wall its on the inside of the inner skin wall?

    for the rest i'd follow the other above suggestions.
     
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  11. backupnorth

    backupnorth

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    Thanks bobasd for advice. I've put in a few more photos which give better insight and I hope some of your points are covered
     

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  12. conny

    conny

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    That rendering needs to be at least 150mm above the outside floor level. It probably bridges your dpc and will certainly not prevent upsplash from falling rain.

    I'd also point out your concerns to the building inspector and if he says things are ok then ask him to put it in writing to you. (He won't).
     
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  13. backupnorth

    backupnorth

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    just one question. The bifold doors open onto level patio ( see pic window and bifld) . What should have been done with regards to the dpc?
     
  14. ^woody^

    ^woody^

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    Didn't whoever did the plans detail the arrangement? Did the work get built to the plans?

    The render is a no-no as mentioned, but you could have the paving level with the cill or floor level as long as a cavity tray and maybe a double DPC is used.
     
  15. martin hill

    martin hill

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    Hi There

    By the looks of the garden it slopes towards the house too. Rain water will run upto the house walls. I'd get the patio taken up leaving a gap between it and the wall so as not to bridge the DPC. Have a drainable channel fitted sloping towards the downpipe drain on the left. My back garden is level with the frenchdoors and slopes up away from the house. I have a 20cm wide trench going 3 bricks below the DPC with decorative gravel in the bottom. When heavy rain the wall gets slightly wet but no issues with damp etc and soon drys
     
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  16. backupnorth

    backupnorth

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    upload_2019-11-5_9-48-14.png

    this is architect's spec

    builder is now talking about k11 tanking. is that a reasonable solution?
     
  17. ^woody^

    ^woody^

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    The builder has not conformed to the spec nor to BS 8215 for the DPC install, or to BS EN 13914-1:2016 for the rendering - so does not meet building regualtions and is a breach of your contract with him. So any remedial works needs to be at his cost, but more importanlty they need to be properly specified by someone with knowledge, and not just the product the builder can get on offer at the merchants.

    Any tanking needs to be considered in context of the potential issues it could create. Also how is this going to stop the cavity fill becoming damp, spreading and then creating a cold spot on that lower wall and potential mould?
     
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