Concrete to basement floors

Discussion in 'Builders' Talk' started by Cratchett, Jan 13, 2021 at 12:45 PM.

  1. Cratchett

    Cratchett New Member

    Hi,

    I have a few questions about concrete floors that I’m trying to get answers to before I contact BC.

    This is a DIY basement refurb with building control approval. DPM has been inspected and OK to pour concrete floors. There are four separate rooms to pour ranging from 13.7 Msq to 3.8 Msq all at 100mm thick. Jabcore hardcore replacement/insulation 100mm thick is installed above DPM with an additional layer of DPM covering ready for concrete. My plans require “100mm of concrete” with no further detail. Site access is terrible and I want to avoid ready mixed and pumping in as it will need to be done in two phases due to room layout. My preference is to do It with a couple of mixers and lots of hard work doing a room at a time.

    Is it a requirement to reinforce the concrete as it has an insulation layer below? If so what type?

    I’ve looked at NHBC standards for site mixed concrete to try and get a guide on what mix to use

    ST 2 or ST3 if un reinforced, ST5 if Reinforced.

    What proportions would a builder use If I got them to do it and would they reinforce it?

    Any additional advice/comments are welcome.
    Cheers
     
  2. stevie22

    stevie22 Screwfix Select

  3. Cratchett

    Cratchett New Member

    Thanks for the reply.
    Do you have any opinion on using reinforcing? I'm going to keep it as simple as possible so I'm leaning toward just cracking on with ST2 concrete.
    Cheers
    Any other contributions or different opinions out there?
    Cheers
     
  4. Severntrent

    Severntrent Screwfix Select

    What is the support under the bottom DPM
     
  5. Cratchett

    Cratchett New Member

    Hi I've pasted in some text from the data sheet for Jabcore below.This is what was approved by BC as access is so tight.


    "Jabcore is a closed cell expanded polystyrene(EPS) panel for use as insulation and replacement for traditional hardcore materials.

    Jabcore-Jablite Hardcore Replacement has been tested and approved by the British Boardof Agrément(BBA) as a structural support and thermal insulation in solid reinforced concrete ground-bearing floor slabs. Certificatenumber 87/1796."

    I'm trying to establish the correct concrete mix and reinforcing to use.
    Cheers
     
  6. Cratchett

    Cratchett New Member

    Just realised I didn't answer what you asked.
    Under the first DPM is 50 mm compacted sand blinding as per product installation requirements.
    Cheers
     
  7. Severntrent

    Severntrent Screwfix Select

    And under the sand?
     
  8. Cratchett

    Cratchett New Member

    Hi,
    Under the sand is the bare ground, bricks and rubble and soil from original construction 1898. All made level and whacker plated.
    All inspected and approved by BC.
    Cheers
     
  9. Severntrent

    Severntrent Screwfix Select

    Ok say you have a compacted sub base that will support your construction with no settlement? in which case there will be no bending stresses transferred through the Jabcore to you concrete slab and as such the slab will not require any reinforcement from a structural point of view if no settlement is envisaged. Your Jabcore appears to have a compressive strength of 4500kg/m2 and since the standard loading on domestic floor slabs is 150kg/m2 I can't imagine the Jabcore will compress to any extent that would cause any undue stresses in the concrete slabs (the 4500kg I believe is based on a value when the slab has compressed to 1% of its thickness but without actually reading the appropriate Standard BS EN 13169 I can not be definitive on this). So the only reason for any reinforcement would be to control shrinkage cracking during curing of the concrete, which, if you you don't make the concrete overly wet and given the size and thickness of the slabs any shrinkage cracks should be minimal if not avoided completely.
     
  10. Cratchett

    Cratchett New Member

    Thanks for the comprehensive reply.
    It appears, from your opinion, that I can use an ST2 or ST3 mix without reinforcement and I can be fairly confident that the loads won't cause any cracking. I'm more likely to get cracks due to the moisture content of the concrete. I'm going to need to get my mix and technique spot on but it looks like I can do a room at a time to keep the costs down. Do you think its worth reinforcing to control cracks from shrinkage? I might try the smallest room without as a test and see how it turns out first.
    Thanks for sharing your in depth knowledge here, much appreciated.
    Cheers
     
  11. Severntrent

    Severntrent Screwfix Select

    Doubt shrinkage will be an issue but if you want belt and braces A252 mesh centrally placed.
     

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