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  • Results 1 to 12 of 12

    Thread: Sodium Bentonite Clay Bottom

    1. #1
      RockPond is offline Junior Member
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      Sodium Bentonite Clay Bottom

      I am building my new Koi pond and plan on using Sodium Bentonite Clay (either Benseal or Cetco Super GelX) to seal the bottom instead of a liner. Sides and some of the bottom are stone and concrete. The dirt bottom is about 12' x 8' (96 sq ft). Water will be about 3' deep.
      Steps:
      Till, rake and compact soil
      Lay down 250 lbs of clay (5 bags), compact
      This is a blanket seal method so I won't be mixing it into the soil
      Cover with 1-2" of sand to confine the clay

      Does anyone have experience with this method?

      I used this video as a reference...
      https://www.youtube.com/watch?v=IkUGu8h73dk&t=116s
      Attached Images Attached Images    
      Last edited by RockPond; 06-23-2020 at 12:19 PM. Reason: images

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    2. #2
      RockPond is offline Junior Member
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      I put some pictures up. You can see why a liner would be difficult to seal it. But I might put one down on the bottom to prevent them from tearing it up. I may dig it deeper if you think that is best, but the slope has to be less than 30 deg from the wall for the clay to stay put.
      It will be a large waterfall with a 8000 gph pump feeding it. Hoping all that rock and sunlight will act as a natural biological filter. What do you think?
      Last edited by RockPond; 06-23-2020 at 09:32 AM.

    3. #3
      pondfishguy is offline Senior Member
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      If you are not concerned about leakage through the walls, why not just pour some concrete.

    4. #4
      RockPond is offline Junior Member
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      I'm worried about the concrete cracking - new england winters. Bentonite is easy to lay down and waterproof forever. I suppose I could pour concrete on top of the sand...

      As for the walls They are 1 ft thick. Granite set in concrete. Not too worried, but I sealed them with greatstuff pond and stone anyway.
      Last edited by RockPond; 06-23-2020 at 10:47 AM.

    5. #5
      RockPond is offline Junior Member
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      I plan to put in 10 baby Koi (3-4") and watch them grow . (If they survive).

    6. #6
      stevek is online now Supporting Member
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      I think you will have leak problems at the stone wall sections. With freeze/thaw over winter, water will get into the inevitable cracks between the stones. You may need to rethink this one...

    7. #7
      pondfishguy is offline Senior Member
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      Quote Originally Posted by RockPond View Post
      I'm worried about the concrete cracking - new england winters. Bentonite is easy to lay down and waterproof forever. I suppose I could pour concrete on top of the sand...

      As for the walls They are 1 ft thick. Granite set in concrete. Not too worried, but I sealed them with greatstuff pond and stone anyway.
      No freeze thaw in submerged concrete. You should reinforce the slab with some mesh regardless.

      I'd be much more concerned in the above grade wall cracking/leaking.

    8. #8
      RockPond is offline Junior Member
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      I plan to put an inflatable pillow in during the winter - should alleviate stress on the walls.

    9. #9
      RockPond is offline Junior Member
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      I sealed the cracks with greatstuff pond and stone - we will see... Skimcoat of cement wouldnt hurt i suppose...

    10. #10
      stevek is online now Supporting Member
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      Quote Originally Posted by RockPond View Post
      I sealed the cracks with greatstuff pond and stone - we will see... Skimcoat of cement wouldnt hurt i suppose...
      I may be wrong, but I don't think I have ever seen a pond with dry laid stones used as a finished wall. Even with the greatstuff sealant, you have a million places for water to seep through when you get the inevitable openings due to freeze thaw of different materials.

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    11. #11
      RockPond is offline Junior Member
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      Yeah - will probably put a skim coat of cement on the inside - thanks. But this is not a drywall its a wet wall with stones on the outside and concrete in the middle and holding them together.
      Last edited by RockPond; 06-24-2020 at 05:21 PM.

    12. #12
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      All five of my ponds are lined with bentonite, though they are far larger in size 1/10th up to 1/2 acre sizes or so.

      One of the drawbacks to bentonite for sealing is that things will burrow through it readily. In my case crawdads and muskrats burrowing from under the water out etc. Then there all the creatures burrowing in like voles, ground squirrels and mice etc... I have a number of leaks in my dams from all of this.

      If you lined the bottom with bentonite clay you could get a mole burrowing up into your little pond. A liner would offer more protection against such incursions than bentonite clay does. Just something that you might think about and consider.
      Last edited by MountainGuardian; 01-28-2021 at 04:37 AM.

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