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Concrete floor slab issue

Discussion in 'Building' started by Jdot, 2 Jul 2021.

  1. Jdot

    Jdot

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    Hi. I am having an extension done and had to be away quiet a bit for work reasons so not always there to see what was happening. Floor slab has been poured about 10 days ago and i noticed the thickness is only around 50-60mm (no mesh). Building plan specified 150mm hardcore, 25mm sand, 1200 dpm, 100mm insulation, 1200dpm, 100mm concrete and 75mm screed.

    Now i am not sure what to do about it now. Is it going to be ok, this is going to be living/kitchen. To get the floor level with existing floor i reckon we are now looking at 100mm screed on top of this slab. Being a novice, can i ask what is the solution now? Can concrete be poured on top of this slab to bring the level to 100mm?Does it need breaking down and re-pouring or i might get away with this 50-60mm concrete slab with 100mm sand/cement screed without major problems in future? Many thanks in advance
     
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  3. Mr Chibs

    Mr Chibs

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    Think I would Scrape off any laitance (if any) then apply a coat of primer Or two, then another layer of concrete to get to where you want.

    Then do you insulation/screed as needed.

    If you can find a volumetric ready mixer supplier, you can just pay for what you need, as they mix as they pour.
     
  4. Notch7

    Notch7

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    put in more insulation

    you could use cheaper Xps for the lower layer to save money -although you are only talking about an extra 25mm
     
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  5. Jdot

    Jdot

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    Thanks for the replies. 100mm insulation is already there under the slab. The problem is with the thickness of concrete slab which is about 50-60mm as opposed to recommended 100mm. So i assume it is not enough? And may crack in future?
     
  6. Have the builders replied to you yet after you asked them why they didnt build to the plan?

    Who designed the floor? What do they say about the difference between what they designed and what the builder built?
     
  7. Jdot

    Jdot

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    Builder is just fobbing off saying it will be ok. Build plan was done by structural engineer but i haven't discussed it with them yet. So is it going to be ok like this now with hardcore, 100mm insulation 60mm concrete slab and 100mm screed or i am looking at issues after a few years?
     
  8. You need to do that as a matter of urgency.

    Dont forget you are also now in the position of not having done what the plans for building regs said.
     
  9. bmb4cjt

    bmb4cjt

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    Did you get anywhere with your 60mm slab issue? Only ask as I'm in a similar situation, extension is divide by a load bearing wall but one part is 100mm thick and one is only 60mm as they didn't leave enough room for UFH etc. Brought it up with them but they said as with you it'll be reet and the building inspector is as much use as a chocolate fireguard.
     
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  11. Jdot

    Jdot

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    Had a chat with structural engg who wasn't happy but still in negotiations to sort it out with added fibre in screed..will keep you posted
     
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  12. bmb4cjt

    bmb4cjt

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    Please do! Yeah asked the structural engineer and he said it's not ideal but will prob be ok, tbh I find our SE like he's doing me a favour, he ain't the most helpful either ‍
     
  13. Jdot

    Jdot

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    My SE is a friend as well so ok on that part but agree with your comments about BCO. Apparently they came down when insulation/dpm was put down before slab pour and also to see air vents extended through the extension. Couldn't they see what was the depth left for slab to be poured on?!
     
  14. bmb4cjt

    bmb4cjt

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    That's what you'd think / expect someone to be doing maintaining building standards, feel they're half checking and take a lot of what builder says on face value.

    Was in when they did the last check at insulation/dpm and all they did was ask the builder guided questions to the answer they're after to which the builder just says, "yep that's what we've done" and off they go. Didn't really inspect anything.

    Has the builder said anything since your friend said he wasn't happy with the 60mm slab or just shrugging it off?
     
  15. Notch7

    Notch7

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    I would say put mesh in the screed - although I'm not sure how strong screed is.
     
  16. Basically, at the builders expense they dig it all up and start again from scratch and do it properly.

    If you dont make them do that then you are colluding in them robbing you.

    And setting yourself up as a soft touch who can be robbed again by them doing shoddy work again.
     
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