Concrete expansion joints - what to use???

Discussion in 'Building' started by cruisey1987, 16 Apr 2019.

  1. cruisey1987

    cruisey1987

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    Hi all,

    First time posting here, found many good answers to DIY questions but haven't been able to figure this one out

    I'm putting down a concrete base for a wooden shed in the garden. Base is 3m x 2.7m and 75mm deep with 75mm gravel underneath

    It's my first time working with concrete and I'm mixing it myself so I'm trying to ensure I've all the bases covered.

    The base will be bordered on two sides, a block wall at the back and a wooden fence at the side. I want to take the concrete right up to both.

    On the fence side I'm going to place a length of treated wood as the border of the form and leave it there. I wasn't planning to put anything between the pad and the block wall

    Now, I'm pretty sure I should put down expansion joints between the pad and the wall/fence. But, I can't figure out how to make them or what materiel to use. The only thing I've found is Flexcell strips below

    https://www.goodwins.ie/products/Flexcell-Strip-12.5mm-150mm-X-2.44-Mtr.html

    I'm thinking I'll place these down on the wall & fence sides before laying the concrete, then cover then with outdoor rated sealant after the concrete is cured. Does this sound right or am I completely bonkers?

    Are there any other materials I can consider as the only place that sells this stuff is a bit of a distance away from me?
     
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  3. cruisey1987

    cruisey1987

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    Here's a picture to help describe what I'm doing
     

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  4. JohnD

    JohnD

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    who is reponsible for the maintenance of the fence and wall?
     
  5. cruisey1987

    cruisey1987

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    Me I would assume, they border onto other houses, not public land
     
  6. JohnD

    JohnD

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    not your neighbour, then?

    you will have to allow room for maintenance, especially for replacement of the fence when the timber rots. And possibly for the rescue of trapped kittens etc.
     
  7. cruisey1987

    cruisey1987

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    I see what you're getting at, the shed won't cover the whole base, there's be about a 30cm gap between the shed & fence/wall, enough to squeeze in to do some small work if needed.

    I know I don't have to take the concrete all the way to the fence, but I'd like a zero maintenance solution for the gap between the shed and fence
     
  8. lostinthelight

    lostinthelight

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    Theres going to be quite a bit of water from next doors and your roof if its a similar design, soaking into the last couple of posts and fence if theres no gutters?
     
  9. ^woody^

    ^woody^

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    You don't need any joints
     
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  11. cruisey1987

    cruisey1987

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    I was going to put a slight slope to the right to drain the water away, but perhaps a drainage gutter would be a smart idea. Probably takes care of my expansion issues too
     
  12. JohnD

    JohnD

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    If the slab is bigger than the shed, try to find a way to slope it so that water runs away, or make the shed-sized section higher than ground level.

    Otherwise water will collect under the shed and cause damp or rot.

    If the slab is inside the shed footprint, the shed will prevent rainwater falling on it.

    Rubbish tends to collect in those small spaces between shed and fence, alowing damp to creep upwards. And people tend to put things in the gap.

    Around utility cabins, a surround of cobbles or other large stones is often left, that can be sprayed with weedkiller a couple of times a year, drains well, and stays fairly clean. Or you could lay a strip of concrete angled like a gutter so that water runs away to your soakaway at the front of the shed.
     
  13. cruisey1987

    cruisey1987

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    So what I found was that I'd need a 50mm drop for the 3m width of the slab, which seems like it'd result in a wonky shed.

    I think a drainage gutter as you describe would be a better approach
     
  14. Tigercubrider

    Tigercubrider

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    My shed is close to the fence. I can just squeeze down for access if I lay off the pies for a while
    I left it as gravel because of. The possible drainage issues
     
  15. Paulg31

    Paulg31

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    no expansion joint is needed. over time the slab will shrink so I'd expect a small gap to form anyway.
     
  16. ivixor

    ivixor

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    Just shove some plywood/osb/chipboard strips between the wall and slab if you want. Doesn't matter if it rots later.
     
  17. DIYnot Local

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