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Concrete floor near damp course, it's up! (with pics)

Discussion in 'Building' started by Scarum, 15 May 2011.

  1. Scarum

    Scarum

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    Hi

    I did make a post yesterday about filling cracks in concrete but I have moved on from that... while chasing out the cracks I noticed a hollow sound and movement of the concrete in some areas.

    Since then I have dug up the channel of concrete between the main kitchen floor and the patio / brick damp course.


    I noticed the DPM doesn’t do all the way to the damp course and has a small split.


    I’m guessing some damp has got in and has attributed to the weakening of the concrete over the years (house is 13 years old), although it doesn't feel damp right now. There was a slight mouldy smell to the concrete when I removed it. The right side of the floor where the patio door opens feels sturdier and there are no cracks.


    Under the DPM are small pieces of breeze block that have been laid as some kind of foundation as shown below, is that good practice?



    Can anyone advise if I need to get the DPM going to the damp course under the patio door? And what material should I have under the DPM before relaying fresh concrete?

    Cheers
     
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  3. hotrod

    hotrod

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    The concrete floor should have been poured / tamped tight up to the vertical DPM section. On one of your pics it appears to finish about 25mm short of the DPM.

    Secondly, how thick is the screed that has been poured over the DPM? In your first pic it only looks about 15mm max - that is not thick enough for a standard screed.

    Take a look at this detail:-

    [​IMG]

    hth
     
  4. Scarum

    Scarum

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    Yes, the DPM is a few cm short of the vertical.

    The bricks under the DPM are elevating it a few cm. Should I remove these bricks, bond together with a good overlap an extra length of DPM to the existing DPM and lay to the DPC, then place a fresh concrete screed over?

    Cheers
     
  5. Scarum

    Scarum

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    I have removed the screed all along here, removed the breeze-block cut offs and will lay some tiles from the the breeze-block foundation to the damp course bricks (to create a bridge). Over that I will extend the DPM with an extra length with as much overlap and infill with fresh screed.

    If anyone interested will post more pics.
     
  6. noseall

    noseall

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    Floor screed will often crack at this junction due to differential movement betwixt the rather stable brickwork against the unpredictable floor.

    Clay substrate is particularly unforgiving due to 'heave' etc.

    The dpm has added to the problem by removing any bonding capabilities within the floor screed.

    We always remove the masonry below allowing the floor screed to have a bit of 'meat' to help overcome the differential movement. The dpm is still continuous but laid down in the trough to maintain damp proofing.
     
  7. Scarum

    Scarum

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    I've spent 2 hours early evening removing the other half of the screed, it was a lot more work to get out because it had no cracks except to the main concrete floor.

    I have removed all large/medium chunks of masonry/screed in the gap. I wormed my fingers down in some parts to find soil (I have a sandy soil). Now I started to panic thinking the damp course isn't laid on a foundation... but then the main wall of the main rear wall of this house is in line with those damp course bricks (as well as the other 4 hours in this terrace). Should I panic or am I paranoid?

    Too tired and hungry to post pics now.
     
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  9. Scarum

    Scarum

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    Rather than laying tiles, is there a cavity closure product I could use instead?

    Cheers
     
  10. Scarum

    Scarum

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    Two bags of screed rubble late last evening...






     
  11. theoldun

    theoldun

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    Mr
    We would confirm with great pleasure that you are 100% paranoid. The cure for that is wacky baccy.
    Your problem is general bad practice on housing sites.
    Your patio door has either been built in with superstructure or cut in after. Either way DPM has been turned over DPC level and then over site concrete laid then DPC
    Floor layer has come along and as top course of footings appears to be blockwork, all he has done is , thrown bit of rubbish in cavity and carried screed into recess over top of poly and DPC, washed his tools and gone up pub, consequently, period of time, crack forms across recess and recess area is hollow.
    To cure.
    Chop approx 100mm deep out of inside skin if blockwork or one course of brick if brickwork. Throw couple shovels of concrete into cavity up to one course below DPC, frame threshold. Throw 12mm of sand over top to blind. Lay new 1200g poly DPM tucked over or under existing DPM across recess and turn up 200mm above door frame patio door. Stick it to glass with bit of tape. If you have no DPM treble up some bin liners, lap well and use them. PVA edge of existing concrete and screed. Knock up a really sandy bit of ballast 4to1, throw it in, tamp her down, level her of and leave until end of day. Then rub her up and polish her off with steel float. Lay skim coat of latex if finish not good enough. Cut of DPM along threshold next day. Carpet will cover.
    oldun :cool:
     
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  12. Scarum

    Scarum

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    Here's what I done tonight, ready for the screed...




    No paranoia now and sleeping well :)
     
  13. Nige F

    Nige F

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    If only all build details were that good ;)
     
  14. Scarum

    Scarum

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    I mixed the screed and laid.

    Made sure it wasn't too wet; followed the rule of creating a cricket ball size, twisting and breaking cleanly in half.

    Yes, I brushed 1:1 PVA/water on the exposed concrete before filling the trench. Used my full weight on one foot to make sure it was well compacted. I plan to finish off with an epoxy levelling compound. Question: is it right I must wait for it to fully dry before doing that? I have covered the screed with bin liners and some vinyl off-cut to stop it drying out too quickly (patio door is south-west facing and it gets hot inside).

    At 6cm deep, should I follow the rule of 1mm per day drying time? Or as it is quite a small volume of screed could I wait less time?

    Cheers.
     
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