Calculating materials needed for concrete slab

Discussion in 'Landscaping and Outdoors' started by MickeyD, Jul 6, 2021.

  1. MickeyD

    MickeyD New Member


    I am going to be pouring a concrete slab as a shed base to the follow dimensions:

    4.8m x 2.7m at 7.5cm thick.

    Thinkin of going with blue circle ready mix bags but not sure how many I would likely need.
    Open to alternative suggestions too.

  2. masterdiy

    masterdiy Screwfix Select

    Have you priced that up?
    Compare it to premix £s. Just so much quicker.
  3. Abrickie

    Abrickie Screwfix Select

    A bag does 0.01 cubic metre :eek:
  4. MickeyD

    MickeyD New Member

    So I am looking at about 100 bags.
    Hmmm.... that would be rather expensive.
  5. FlyByNight

    FlyByNight Screwfix Select

    You are looking at around 1 cubic metre off all in one ballast plus maybe 15 bags of cement. Cost around £150 ish.

    A bulk bag typically contains around 0.5 cubic metre.

    Using ready mix bags - 100 of them at around £5-6 each, so £550

    IN both cases you will have mixng time too. Be very sure of the depth, is it onto a firm base or into rough hardcore. Will you need a little more than 1m? you might if itis actually 80 or 85 mm.

    Also, get some polyester fibres and add a handful to each mix.
  6. Jord86

    Jord86 Screwfix Select

    I know it's nice to work hard and all, and there's a deep sense of satisfaction in calculating, mixing and laying the measured quantities out perfectly, but I would at least enquire with the local volumetric-mix it on site concrete suppliers how much they would charge for a cube, if it's in the region of £2-250 then I would bite their arm off and save all the faffing about.
    FlyByNight likes this.
  7. MickeyD

    MickeyD New Member

    Bulk bags of ballast are a possibility.
    It is a very solid foundation. I have put down type 1 MOT plus a layer of self-binding gravel on top. A little overkill but it isn't going anywhere.

    Will look into volumetric mix too. The only other company I found was Spotmix.

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