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Is it ok to bury concrete rubble under garden?

I'm knocking down a garage in my garden.  The builder has broken up the concrete slab but is stating the it should be ok to bury the rubble.

I'm less certain.  A broken up concrete slab will contain a lot of alkaline. I'm also concerned about drainage.  

If left, the rubble will be ~ 40cm below ground level.  Part of the buried area will be turfed, part will be planted with flower beds.

Advice appreciated!


  • KT53KT53 Posts: 8,035
    I'm probably missing something, but how will base slab rubble end up 40cm (16") below ground level?  By definition, a garage slab will be at ground level when in use.  It would be far better to get it off site.
    Ground below the slab will be very compacted and may well cause drainage problems.
  • Thanks for the quick response.  My house is on a hill. The garden falls away from the house.  My driveway is ~1.6metres below the floor level of the house. A previous owner built a garage in the garden and sunk it into the garden.
  • LoxleyLoxley Posts: 5,232
    If well broken up, it's certainly possible to have a nice garden on crushed rubble, if you have a reasonable depth of topsoil over the top (40cm is reasonable). The lawn will be OK, but it will alter what you might want to plant in the beds. Because of the lime in the concrete and the drainage it will provide, you could think of it like gardening on chalk. Roses might struggle a bit, Rhododendrons would be out, but most of the classic 'Mediterranean' herbs and perennials would love it.

    What is the native soil like? If you weren't re-using the crushed rubble, would you need to import material to bring up levels?
  • How should the soil compaction issue be dealt with? 
  • The soil is full of flint and roses grow well if that helps.  The hole will be filled in with a mix of excavated soil from other areas of the garden (we're having a patio and a new driveway laid as part of the job) and new/imported soil.
  • raisingirlraisingirl Posts: 6,645
    edited April 2021
    What's your general soil like? In effect you're building a large soakaway, in principle the same as many gardens will have somewhere, taking the rainwater from the house roof. It's fine. The only caveat is if you have very heavy clay soil, it will form a sump in winter which gets very wet. If your soil is reasonably free draining, I can't see any issue with it. You won't particularly raise the lime content with old concrete. Plasterboard/gypsum can have that effect, but concrete that has 'gone off' is pretty stable - it won't degrade much so it won't leach cement - or only very very slowly

    As has been said, chose the plants with care for the situation
    “Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first” 
  • Thanks for the feedback.

    The soil in the general area is flint / clay.  I have an allotment across the road from my house which was grass and compacted soil when I took it on.  I have spent a lot of time pulling our rocks from the ground and improving the top soil.  In the back garden there's a thick layer of topsoil in the beds, I guess below that there's a similar flint / clay subsoil.

    I have the opportunity to ask the builder to take away the rubble or offer to pay for a bit more effort to do so.  I'm concerned that if I don't, I'll live to regret it.
  • DovefromaboveDovefromabove Posts: 83,837
    My instinct would be to get rid of it ... there'll be a Landfill Charge if it goes to a tip, but some builders crush it and sell it on as hardcore  ... if you bury it you'll be governed by the fact that it's there if you ever change your mind about what you're going to do with that area ... but if you're really convinced you won't ever change your mind then go ahead and bury it nice and deep. 

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.

  • FireFire Posts: 17,116
    I would suggest removing it else some poor sod in the future is going to have to deal with it. It's a bit like finding a garden full of buried bicycles and fridges.
  • Thanks for the quick response.  My house is on a hill. The garden falls away from the house.  My driveway is ~1.6metres below the floor level of the house. A previous owner built a garage in the garden and sunk it into the garden.
    I like your house.... a bit small but very pretty.  :smiley:

    Yeah, I'd bury it. 400mm is fairly deep and if its crushed fine enough shoudn't be an issue. You may want to consider advertising it on freecycle (or similar). Sometimes other people will want a small amount of hardcore. I wouldn't, personally, want to cart it to the tip - too much like hard work - on both yer back & car.

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