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  1. #1
    Senior Member Rank = Yonsai Tropheus's Avatar
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    Cavity Block Build

    Hi,

    Thought I'd create a separate thread rather than this get lost in my main build thread.

    My pond will be 2.5m x 4m x 1.5m with a smaller raised pond of 2.5m x 1m x 0.6m to be used as an anoxic filter and waterfall return. I'm pretty much settled on a cavity block build with vertical rebar and backfilled with concrete. My pond will be rendered and painted rather than fibreglassed.

    I've also seen others not using mortar between the cavity blocks. I'm not sure of the advantage, but will likely mortar.

    I will have vertical rebar for support. Do I need to add horizontal rebar for additional support? I noticed this on a couple of builds on a US forum and it's not something I considered or noticed with builds here.

    I'm likely getting into the realm of over-engineering.



  2. #2
    Senior Member Rank = Yonsai Tropheus's Avatar
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    This is the sort of thing I'm talking about. Seen it done along straight sections and also bent around the corners for additional support. Not done at every layer of bricks, but at bottom, middle and top of build for stability.

    Do people do this and I just didn't cop it previously or is it overkill?

    rebar.jpg

  3. #3
    Senior Member Rank = Yonsai Tropheus's Avatar
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    These blocks appear to have a groove for laying rebar horizontally. I'm thinking it's probably worth doing for the price of a bit of extra rebar.

    I'd hate to have the job of demolishing this pond in the future

    https://grange.ie/builders-providers...y-blocks-215mm

  4. #4
    Extreme Koi Member Rank = Sansai Hawk101's Avatar
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    I've just doubled the size of my pond and the extension is built with 9" hollow blocks dry stacked (no mortar joints).
    I've installed rebar into every hollow chemical anchored it into the concrete base and filled the hollows with concrete.
    I also ran a horizontal rebar every other course which is also chemical anchored into my existing pond wall.

    Not sure how much of your pond will be out of the ground but for the cost of a bit of rebar I would install as much as you can.

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  6. #5
    Senior Member Rank = Yonsai Tropheus's Avatar
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    Quote Originally Posted by Hawk101 View Post
    I've just doubled the size of my pond and the extension is built with 9" hollow blocks dry stacked (no mortar joints).
    I've installed rebar into every hollow chemical anchored it into the concrete base and filled the hollows with concrete.
    I also ran a horizontal rebar every other course which is also chemical anchored into my existing pond wall.

    Not sure how much of your pond will be out of the ground but for the cost of a bit of rebar I would install as much as you can.
    Thanks. That's what I'll do then. What do you mean by chemical anchoring?

  7. #6
    i built my pond using those, just bedded the 1st course and drilled holes in the slab every other cavity for the rebar, dry stacked the blocks and filled the cavities with concrete, really fast build and easy too. no need to chem fix anything or for horizontal rebar in my opinion, ill warn you those blocks are HEAVY though

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  9. #7
    Senior Member Rank = Yonsai farmergoggin's Avatar
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    Quote Originally Posted by Tropheus View Post
    Thanks. That's what I'll do then. What do you mean by chemical anchoring?
    You can drill a hole for the rebar to sit in/slide into and pump in a resin which sets rock hard.

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  11. #8
    rebar aint going anywhere when its incased in a 4 inch column of concrete, just drill a hole and drop it in

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  13. #9
    Extreme Koi Member Rank = Sansai Hawk101's Avatar
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    Quote Originally Posted by Tropheus View Post
    Thanks. That's what I'll do then. What do you mean by chemical anchoring?
    As has been said mate, there is probably no need for you to fix your rebar as its a complete new build.
    I was tying into my existing pond so drilled into the floor and walls at the join and used resin to anchor the join.

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  15. #10
    If you decide to bed the blocks in mortar make sure the mortar does not impede you pouring concrete down the insides of the cavities. Stacking them without mortar and then pouring concrete into them with rebar will make a very strong wall.

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  17. #11
    Senior Member Rank = Yonsai Tropheus's Avatar
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    Quote Originally Posted by the coyman View Post
    If you decide to bed the blocks in mortar make sure the mortar does not impede you pouring concrete down the insides of the cavities. Stacking them without mortar and then pouring concrete into them with rebar will make a very strong wall.
    Good point. I'll recommend dry stacking to the builder.

  18. #12
    Quote Originally Posted by Tropheus View Post
    My pond will be rendered and painted rather than fibreglassed.

    Are you sure about this?

    I mean really, absolutely, sure?

  19. #13
    Senior Member Rank = Yonsai Tropheus's Avatar
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    Quote Originally Posted by MustBeSomethingInTheWater View Post
    Are you sure about this?

    I mean really, absolutely, sure?
    Yes, I've given it a lot of consideration. I'm in Ireland and, unlike the UK, ponds of this scale are rare and we don't have people that specialise in this area.

    I reckon it would cost in excess of €2,000 and could end up being a bad job as the person how does it will never have done one before. I also have no control over them using a fish safe product.

    If this changes and I decide to do it in the future, I can go that direction. For them moment it's being painted.

    I understand why you're asking as it's rare to see a painted pond on here.

  20. #14
    Senior Member Rank = Nanasai algarth's Avatar
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    Have a word with Ken Alexander on here about fiberglassing and yes it isnt cheap but its permanant. you will be having to repaint quite frequently loosing good water and filter bacteria. Plus where do you put your fish whilst doing it?
    If its square or rectangle or a simple shape you can get box welded liners too
    Quote Originally Posted by Tropheus View Post
    Yes, I've given it a lot of consideration. I'm in Ireland and, unlike the UK, ponds of this scale are rare and we don't have people that specialise in this area.

    I reckon it would cost in excess of €2,000 and could end up being a bad job as the person how does it will never have done one before. I also have no control over them using a fish safe product.

    If this changes and I decide to do it in the future, I can go that direction. For them moment it's being painted.

    I understand why you're asking as it's rare to see a painted pond on here.
    Last edited by algarth; 09-07-2020 at 09:06 PM.

  21. #15
    Senior Member Rank = Yonsai Tropheus's Avatar
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    I had paint on my previous pond done 3 years ago and it was still perfect.

    I appreciate it's not as permanent as fibreglass, but just not an option.

    I had a word with Ken and he has no plans to travel to Ireland at the moment. The cost of expenses on top of a single job wouldn't be viable.

 

 

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