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Clayboard requirement if using piling ?

Discussion in 'Building' started by Cypermethrin, 20 Mar 2017.

  1. Cypermethrin

    Cypermethrin

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    NWe are getting quotes to pile foundation a 4.5 x 1.8m utility room which is single storey and single bricked utility room. It was built at the back of the single story kitchen extension built in 1977(ish) and has signs of slipping into the adjacent brook - although its hard to tell if its recent or old movement.

    We moved in last November - we are located near Reading in what the geo-maps say is London Clay

    We have had 6 quotes for piling and RC slab foundations ranging from 7 to 11kGBP

    Only one of the contractors has come back with the potential requirement to have Clayboard installed on the piles before the slab at an additional cost of 2k

    http://clayboard.co.uk/products/residential-clayboard/

    I thought that as the piling were 6+m deep and the slab built directly ontop that accounting for any clay heave would NOT be required

    Thanks for your counsel in advance

    Tim
     
    Last edited: 21 Mar 2017
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  3. tomfe

    tomfe

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    I would like to know how you can put clay board beside your piles.

    Is your slab ground bearing?
     
  4. russellsmiler

    russellsmiler

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    have you any drawings from a S/Engineer regarding the pilecap, and ring beam, (as a strip foundation) or are the piles installed on a grid with a RC (sub) slab??
    Clayboard may need to be installed if the soil conditions dictate.
     
  5. Cypermethrin

    Cypermethrin

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    Thanks for your reply - the piles are proposed to be installed on a 200mm thick reinforced concrete stab with 110mm Clayboard underneath resting on the pile
     
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  7. russellsmiler

    russellsmiler

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    I am uncertain what you are doing? You say the utility WAS built, so is this a stabilization job??
    surely you mean the RC slab will be cast on top of the piles? I assume you have a piling layout??
    If it is piling within the already built utility then will the existing floorslab be removed?

    the clay board should lie as a barrier for the subsoil (clay) and the concrete. the piles have to be cast into the slab. there will be no barrier of clay board between top of pile and slab.

    9M2 of clay board should not cost much, although there is the excavation that the board will displace to consider.

    But please a better description of your project!
     
  8. Cypermethrin

    Cypermethrin

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    You are quite right - my description is not great so I'll try again.

    • Single story existing utility room 1.8 m x 4.1m build sometime in 1977 on back of single story kitchen extension of the same date.
    • Utility room shows sign of slippage to one side - has approx. 10 mm gap in masonary between utility wall meeting kitchen wall - gap is linear top to bottom
    • Utility room runs adjacent to small brook which runs 1 m below it and approx. 1 m from utility room wall
    • Utility room single bricked and build on a concrete slab which is clearly not sufficient
    The Plan
    1. Without demolishing the utility room install new piled foundations resting on reinforced 200mm concrete slab
    2. Only one company I have approached has claimed to be able to do this without demolishing first
    3. Their proposal was
    a) Taking up floors and reducing levels
    b) installing the piles up to the allowed depth
    c) breaking out and supporting below walls
    d) installation of clayboard and reinforced concrete slab

    Having spoken to the company they have explained that of course the slab would rest directly on the piles - but the Clayboard would provided gap between the substrata and the concrete which would then degrade over time leaving a gap between the substrate and the new concrete slab to account for any clay heave

    My contention is the clayboard and is it really needed as the quote for it is 2kGBP extra (!)
     
  9. russellsmiler

    russellsmiler

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    Right its looking clearer
    Yes the 2k for clay board is excessive. its 9M2 the board itself should be circa £25.00 M2 making it a £225.00 purchase the dig off for this board is 110mm x 9000mm = less than 1 M3 another £300.00 (MAX) = placing board etc £100.00 Max , so should be sub £700.00 for clay board item of this work.

    Must admit though , a single skinned utility of this size?? spending 11 K just to stabalise it seems a big investment.

    Just one last note. breaking out and supporting below walls, they will not break out completely and support your utility ( this is almost impossible as the supports would have to be cast in, find out more about this support, It would have to be a hit and miss system.
     
  10. Cypermethrin

    Cypermethrin

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    Thanks again for help - and I am right there with you wrt the costing for what is essentially a utility room. Even if I demolish it and remove the existing slab to get piled foundations installed would be 7k from the cheapest contractor - then cost of the new brick work and the roof rebuild - so that would take it to probably nearer 10k. So either way its way too much for a small utility room in my view.

    The contractor I spoke to about retaining the existing structure and underpinning advised that the supporting walls would be supported by steel pins at 3 foot interval as the foundations are removed; these would then remain in situ whilst the piled r/c slab is cast and set; apparently they have done this for whole streets of terraced houses previously and seem to knoiw what they are talking about.

    I will ask the contractor about the 2kGBP for the Clayboarding - I could see this being accurate @ 2k if they did proper soil testing at a lab to determine if its required - so that is what they may have factored into the quote
     
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