cost of new concrete slab??

Hello all,
I live in a bungalow in west Wales (built 1970) with concrete floors throughout.
Whenever we have heavy rain, a large water stain appears in the middle of my lounge carpet.

After some investigations, it does seem that the Damp Proof Membrane beneath the concrete slab has been breached - allowing a serious amount of water to leak into the concrete floor in heavy rain.

The entire footprint of the bungalow is approx. 8m x 14m, but the damp/leak appears to be limited to the lounge which has a total floor area of about 4m x 5m.

What would be the approximate cost of digging up the concrete floor, replacing the DPM & then re-concreting this 4m x 5m area?

Thank you.



Comments

  • Bigphil1474
    Bigphil1474 Posts: 2,289
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    I don't know about the cost, but a damp proof course isn't designed to stop leaking or floods. You need to find out where the water is coming from. They are only really to stop rising damp, whereas it sounds like you have something more major affecting you. Could be a damaged drain if its rainwater
  • stuart45
    stuart45 Posts: 3,823
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    Prices will vary a lot, but it will likely be in the £8,000 range. Depends on the size of the firm, whether you want the floor screeded, any pipes etc in the floor, skirting etc put back.
  • gwynlas
    gwynlas Posts: 1,622
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    You should have some investigative works carried out to seek the source of this problem. I once moved into a flat where the kitchen/bathroom extension underfloor membrane had not been installed so the whole slab was replaced. This was over 30 years ago so no idea of current costs but it will be a huge disruption.
  • Thank you for those comments.
    Yes, I agree it would be good to know where the extra water is coming from exactly...
    A firm is coming round next week to investigate.

    To explain the lie-of-the-land, my (rectangular) bungalow sits on a slope, so that the one long edge (& floor) is much higher above outside ground level than the other long edge. 
    My leak is in a room where the floor level is a good 12" to 18" above the ground outside.   ...so it seems that the 'extra' water is being 'drawn up' into the house.....
    Is that possible or likely do you think?

    Stuart45: That ball-park figure of £8000 you provide...   that's for just re-concreting the 4m x 5m lounge floor area, correct?

    I have my own theory [nightmare] about the cause of this leak:
    About 3 - 4 years ago, there were some quite major roadworks done in the vicinity; new junction & traffic lights.
    Then, a year or 2 later, a sudden strong spurt of water appeared through the road-tarmac within 25m of my bungalow; literally water was gurgling up and across the road...
    The road was dug up and the 'leak' fixed.
    Could the underground drainage in the area have been disturbed by the major roadworks a few years ago, and an underground spring diverted to under my property?

    Thanks for sharing your experience & knowledge.
  • Section62
    Section62 Posts: 7,504
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    gutovicky said:

    To explain the lie-of-the-land, my (rectangular) bungalow sits on a slope, so that the one long edge (& floor) is much higher above outside ground level than the other long edge. 
    My leak is in a room where the floor level is a good 12" to 18" above the ground outside.   ...so it seems that the 'extra' water is being 'drawn up' into the house.....
    Is that possible or likely do you think?

    Possibly, but very unlikely.  Surface water will flow to the lowest point, and unless there is something unusual about the fill under the floor slab, ground water will drain away to a lower level.  You'd also expect quite a delay between rainfall and a build up of ground water enough to make its way up through the floor construction.
    gutovicky said:
    Could the underground drainage in the area have been disturbed by the major roadworks a few years ago, and an underground spring diverted to under my property?

    Again possible, but I wouldn't think the most likely.

    If I were to take a guess - not seeing the property or knowning much about it - I would wonder whether the issue might be central heating pipes buried in the concrete floor slab and one of them has started leaking.  In the 1970's less care was taken with underfloor pipework, and a cheaper grade of pipe was in common use to save copper (and money).

    Well-made concrete is relatively impermeable to water, so unless the quality of the concrete is also poor, I wouldn't really expect "a serious amount of water" to get through it in a short enough time-frame to definitively link it to rainfall.

    Have you had the water tested to see if there is any indication of source?
  • stuart45
    stuart45 Posts: 3,823
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    gutovicky said:
    Stuart45: That ball-park figure of £8000 you provide...   that's for just re-concreting the 4m x 5m lounge floor area, correct?

    Rough guide for breaking up the existing and pouring a new one. Based.on the cost of work for slabs with a sulphate attack. 
    Obviously you're not going to start ripping out the floor without expert advice on the cause of the problem. 
  • 35har1old
    35har1old Posts: 953
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    stuart45 said:
    gutovicky said:
    Stuart45: That ball-park figure of £8000 you provide...   that's for just re-concreting the 4m x 5m lounge floor area, correct?

    Rough guide for breaking up the existing and pouring a new one. Based.on the cost of work for slabs with a sulphate attack. 
    Obviously you're not going to start ripping out the floor without expert advice on the cause of the problem. 
    Solid floors are usually made up of a base of concrete then insulation placed on top which usually contains  heating pipes and then a screed of sand and cement
  • stuart45
    stuart45 Posts: 3,823
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    35har1old said:
    stuart45 said:
    gutovicky said:
    Stuart45: That ball-park figure of £8000 you provide...   that's for just re-concreting the 4m x 5m lounge floor area, correct?

    Rough guide for breaking up the existing and pouring a new one. Based.on the cost of work for slabs with a sulphate attack. 
    Obviously you're not going to start ripping out the floor without expert advice on the cause of the problem. 
    Solid floors are usually made up of a base of concrete then insulation placed on top which usually contains  heating pipes and then a screed of sand and cement
    Not in the 70's. Normal floor was hardcore, sand, DPM, 4 inches concrete, 2-3 inches sand/cement screed.
    '
  • 35har1old
    35har1old Posts: 953
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    edited 5 November 2023 at 8:23PM
    stuart45 said:
    35har1old said:
    stuart45 said:
    gutovicky said:
    Stuart45: That ball-park figure of £8000 you provide...   that's for just re-concreting the 4m x 5m lounge floor area, correct?

    Rough guide for breaking up the existing and pouring a new one. Based.on the cost of work for slabs with a sulphate attack. 
    Obviously you're not going to start ripping out the floor without expert advice on the cause of the problem. 
    Solid floors are usually made up of a base of concrete then insulation placed on top which usually contains  heating pipes and then a screed of sand and cement
    Not in the 70's. Normal floor was hardcore, sand, DPM, 4 inches concrete, 2-3 inches sand/cement screed.
    '
    So just minus the insulation
    What about the reinforcing?
  • stuart45
    stuart45 Posts: 3,823
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    Re-bar wasn't normally used. Concrete floors only became really popular after WW2 because of timber shortages. Up to the mid 60's a DPM wasn't part of the regs. As with most things in the building trade, it can take years to discover mistakes in the methods. Deep hard-core fills can result in the slab cracking. The fill next to the trench was usually a lot deeper. The DPM was usually cut off flush with the blockwork, rather than lapped into the DPC. The DPM wasn't often lapped or taped properly at the joins. Labourers often made holes in it to let out the water. 
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