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  1. #1

    wall construction

    I'm just in the planning stage for a smallish pond... proposed dimensions approx 12' x 5' and 4' deep. Simple rectangle... about 7000l by my calculations. I'm planning to dig down around 18" and then the rest will be above ground... so the rim will be about 30" high. I'm planning on putting a concrete base down of the full dimensions, at the bottom of the pit, and then building the walls up from this using breeze blocks (like these). To get the height I think I'll need to use 6 blocks high, 2.5 of them will be below ground level. Questions are:

    Do I need to use metal bar in the base pad?
    How thick should the base pad be and what should the mix be?
    What size bead of mortar between the blocks?
    Will the walls be strong enough simply built up with mortar like a brick wall? I guess I need to render it once built?
    Anyone suggest any alternative methods that might be better, preferably cheaper?

    I'm planning on incoprorating a bottom drain, skimmer, windows and using pond paint (at this stage). I'll have the filter system a few metres away in a small bunker.



  2. #2
    You’re doing a single skin of blockwork if I read your post correctly?
    Welcome to the forum by the waywall construction


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  4. #3
    thanks :-) yes. Those blocks are 100mm thick. Am I underestimating strength required? Roughly half of it is below ground level...

  5. #4
    Subjective lol
    Personally, I wouldn’t use s single skin but someone will be along and say it’ll be fine. Although I’m all for “no overkill” 100mm block walls just don’t sit right with me. They’re just too wibbly wobbly for my liking.
    If using single skin then I’d say that most people would then add a second skin of facing brickwork tied to the inner skin to finish it nicely and provide additional strength.
    For your size pond I’d consider using sleepers. You’d get away with putting them in “tall way” up as opposed to flat so that’s gonna save you a few quid.
    Construct a concert collar and dig out your depth. Build your sleeper walls off the collar. Line it all with ply and celotex then put a box liner in. You won’t need a concrete slab then either, more money to spend on filters and fish
    Search the site for “sleeper” and there’s loads of examples plus they look pretty cool when they’re done properly.
    Have a few days browsing the other builds for ideas too. Makes great I-poo reading, especially Felines which is epic.
    Had a discussion recently with someone else about pond paint...I’m not a fan of that either. I’m pretty confident you could get a good quality box liner for the same money you’ll spend on paint.
    Other people may disagree but it’s an option to consider?


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  7. #5
    If you completely diss my idea then I’ll tell you more useless stuff wall constructionwall construction


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  9. #6
    thanks - no that's really useful. Definitely food for thought. I'm at very early stage so will consider anything :-)

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  11. #7
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    Quote Originally Posted by clippo View Post
    Do I need to use metal bar in the base pad?
    Yes. reinforcing mesh. 8mm with 200 mesh would be sufficient. it helps stop the base cracking if the ground moves

    How thick should the base pad be and what should the mix be?
    depending on ground conditions, but 150 should be ok, 200 at most. no need for a special mix. 1:3:5 or thereabouts is ok.

    What size bead of mortar between the blocks?
    Std mortar bead is 10 to 12 mm

    Will the walls be strong enough simply built up with mortar like a brick wall?
    No. You really want the 215 thick blocks. with 10mm+ rebar through about 1/3 to 1/2 through the cavities into the base and back filled with concrete. Water pressure will be pushing outwards and with most force at the bottom. A ring of rebar around the walls mortared in is stronger than verticals if you can incorporate it. Many get away with less it seems and your depth isnt great,.. but if you want to be sure...

    I guess I need to render it once built?
    Depends what you want to line it with. if box liner or fibreglass. no,

    [quote]Anyone suggest any alternative methods that might be better, preferably cheaper?
    What big carpchaser said...

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  13. #8
    thanks - wow, sounds like it's going to really bump the price up if I go that route.... will investigate the sleepers I think as I did originally want a wood finish anyway. I realise the depth isn't massive but I'm not actually planning on Koi, at least to start with anyway. I will probably go for half a dozen good quality Shubunkins (Londons if I can find any) and maybe a couple of individuals fish... tench maybe. If it all works well over a couple of years I might swap them out for half a dozen smallish Koi. I'm planning to build an arbour over the pond and to incorporate removable polycarb cladding/panels that can be emplaced over the winter to turn it into a greenhouse of sorts, so that should stop it getting too cold hopefully (gives me somewhere to furtle about too!). I'm also planning on using rainwater for an automated top up system and to incorporate a hydroponic filter somehow. Maybe to grow water cress, water chestnut... very early days yet though :-)

  14. #9
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    Quote Originally Posted by clippo View Post
    thanks - wow, sounds like it's going to really bump the price up if I go that route....
    It's not bumping the price up. You under estimated.


    besides its still cheaper than digging it up and doing it again

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  16. #10
    okaaay. Just trying to get my head around this... so as an alternative to the wall method, could I dig out a foundation trench, fill this with concrete and then build my sleeper wall on top of that? (seems to be what folks are doing in the sleeper threads). Then dig out the middle down to the base of the concrete foundations?

    If that's the case, surely the concrete foundation walls aren't a massively better option that a single skin wall held by earth are they?

    Are there any sites which allow one to actually calculate the forces involved as there seems to be the potential for underestimating or massive overkill here (and I don't have money to burn)

    Anyone know cheapest place for sleepers? If I do the foundations to ground level and then sleepers above ground it looks like I'll need 15... which comes to £500. Would be nice to get this down a bit.
    Last edited by clippo; 13-06-2018 at 04:06 PM.

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    If it's only coming 2 foot out of the ground then you don't need to go nuts really.
    What you can do is use the blocks upright as you were thinking up to ground level, then backfill around and lay a shallow concrete collar round the outside, and lay the above ground blocks flat (so the wall above ground is 20cm thick not 10). It is absolutely fine to just build in cement like a wall. You don't need rebar in 7N concrete blocks!!

    Using twice as many blocks above ground will obviously add to material costs and mean more sand and cement too, but it's not mahoosive.

    I would scrap the pond paint idea though- go with box weld liner or fibreglass and spare yourself the trauma of a leaking painted pond. If you were going with a liner you actually have the option of not using a concrete slab at all if you are keen to keep costs down. You can just make a concrete collar foundation for the walls and build up from that, and level the base off with sand to protect the liner. There are lots of options really.

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  19. #12
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    hmm... where does it say he is using 7N blocks? I read the question as 100mm hollow blocks....


    EDIT : Ok i see the link in the OP's original message - i could swear that was a link to narrow hollow blocks when i looked...

    My apologies - insomnia is getting to me.

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  21. #13
    cool. thanks! I'm planning on hiring a mini-excavator for this as I've got back problems... so I may well go with the original idea plus the flat blocks above ground as suggested as this allows me to just dig the entire hole to start with. I'd then build the single skin with backfill to ground level, then lay blocks flat above ground. Box weld sounds like the best option...

  22. #14
    Extreme Koi Member Rank = Yonsai muttley's Avatar
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    Standard mortar bed thickness is 10mm....Not 10-12. 225mm including bed for blocks and 75mm including bed for bricks..

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  24. #15
    just been researching this a bit over the last few days.... do folks think that rather than go with 440x215x100mm blocks laid flat I could instead go with 440x215x140 blocks standing up? I think the cost is fairly similar... it's just with the 215 thick walls in the first scenario, I am loosing quite a bit of pond volume given the space available. This is just for the half of the pond that is above ground... the lower half to ground level would still be backfilled 100mm blocks standing on a concrete base foundation of a few inches deep and then the bottom would be levelled, sanded and lagged (with something) for the box weld to sit on?

  25. #16
    quick sketch-up diagram... isn't finished yet. No capping stones, no riser in the centre rear for spillway structure, no pipework... note 'box' in rear corner which will ultimately be the filtration bunker. Limited on textures also so they aren't final.

    screengrab.jpg

  26. #17
    having thought about this for the last couple of weeks I am now considering digging out a foundation trench to a depth of about a foot and pouring concrete into this. Then I plan to build the above ground walls on top of this using 140mm hollow blocks to a height of about 2ft. I plan to insert 10mm rebar down through these also. Once that's done I will dig out the centre down to the bottom of the foundation wall and then another foot at least. At the bottom I'll be installing the drain and then a layer of sand before underlay and then box weld liner.

    Some questions.

    1) Is 12" deep enough for the foundation collar
    2) Does the rebar need to go down into the collar? (if so, do I put them in before the blocks... or drill the concrete??)
    3) How deep do they need to go into the collar?
    4) How do I get a nice flat finish on the inside walls of the collar so that it doesn't present an uneven surface once the centre is excavated?
    5) do I need to clad the insides, particularly the level which is below the concrete collar... as this will just be earth... I need to protect against roots I guess?

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  28. #19
    Senior Member Rank = Grand Champion voodoo_15_uk's Avatar
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    wall construction

    Can I ask why you want to do it that way and not dig all out first, lay base then build up?

    It will be very difficult to get a level even wall if dug out and you risk compromising the collar my digging down the side of it. You risk subsidence if the underlying soil becomes dislodged.

    You would have a slight shelf too as foundations usually need to be wider than the blocks to ensure stability.

    The rebar can be cut into smaller pieces so it’s half in the base and comes out enough to go half way through the block.

    What are you planning on lining the pond with?


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  30. #20
    thanks Laura - only considering it as I've seen sleeper ponds built in this way... but very good points! My initial plan was to build a flat base so maybe I will go back to this idea. Just means shifting more earth and buying a more blocks but hey-ho. I guess I could put the rebar right down through the 6 levels of blocks. Planning on a box welded liner :-)

 

 
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