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Duh a hole, it’s drenched, need to concrete

Discussion in 'In the Garden' started by ryanwatson, 3 Feb 2021.

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  1. ryanwatson

    ryanwatson

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    So, this so my first concrete experience so I’m truly new to all of this. I have probably done this at the wrong time of year, but I’d like to try and find a way around it if that’s at all possible.

    I have dug a hole aprox 4 x 2.8 meters and hit a gutter pipe drainage on the way which I’m digging around to reroute. It’s been very wet over the past week and caused water levels to rise in the hole a little out of control. I have tried draining it as you see in the picture, this works but hours later there’s about 10cms more until it settles l suggesting a high water table.

    I need to lay a concrete slab (a little smaller than the hole), my current plan is as follows:

    1. Put a tarpaulin over the hole to stop any rain, I’ll need this for concrete due to the time of year
    2. Wait for the water to drop a little - hoping for a week or two
    3. Remove about 10 cm of muddy clay soil
    4. Add some rubble, I’ve got some just laying around, tamper it a small bit, I suspect this will be muddy still
    5. Put down a huge plastic sheet preventing water from the walls seeping in
    6. 4 inches of MOT1, tamper it down
    7. Pour 4 inches of concrete on top, I have some timber for supports

    Is this doable, is there another way... looking for some advice really. Thanks all.
     

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  3. johnny2007

    johnny2007

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    Pour the concrete.
    A little water will not make any difference.
    I've seen concrete being poured in what looked like half filled ponds, water floats out of it, doesn't mix.
     
  4. kingandy2nd

    kingandy2nd

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    Be careful with re-routing that pipe - you should have an inspection chamber at each change in direction really, or at the very least some swept bends in the pipe.
     
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  5. JohnD

    JohnD

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    scoop out the water and any soft mud

    shovel in well-mixed but DRY mix and tamp down well. It will absorb moisture from the wet ground later.

    mix up the rest of your concrete, just enough water to lubricate it so it will flow

    add the rest and tamp down well.

    If excessive water rises to the surface try not to overtrowel it. The creamy wet paste will lie on the surface and will form a weak crust when the rest has hardened.

    A technique used for utility cabins where readimix will be used, in wet weather, is to scrape out the mud and immediately lay a dry lean mix first and tamp down well to absorb the moisture and leave a clean bottom, then pour the readimix onto it so it will not be contaminated and weakened by mixing with mud.

    You can put a dpm on the drylean if you want. This will also prevent mixing with your main mix and keep it clean. It will get wet enough to properly cure later.
     
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  7. ryanwatson

    ryanwatson

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    Should have mentioned it’s semi structural as it’ll need to house a 6 ton water filled spa. Having a go like this worries me.
     
  8. JohnD

    JohnD

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    the drylean base is a correct and recognised technique.

    Tipping readymix into a muddy pond isn't.

    You can use sacrificial ply boards as shuttering to prevent mud from the sides getting in.
     
  9. ryanwatson

    ryanwatson

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    Some great advice on both your points l, thank you I’ll see what I can do with that
     
  10. ryanwatson

    ryanwatson

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    Inspection chamber is less than ideal so I’ll avoid if I can, but I’ll certainly now look for swept bends instead of putting in an elbow, this makes a lot of sense thinking about it.
     
  11. DIYnot Local

    DIYnot Local

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