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  • Results 1 to 13 of 13

    Thread: Liner over concrete?

    1. #1
      EDT is offline Member
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      Liner over concrete?

      Has anyone ever used liner on concrete? I have my pond dug out at 5 feet deep and I want the stability of concrete but I'm worried about cracks as I plan on using a thin layer, maybe 2-3 inches thick. I've heard people putting liner down and then concrete on top of it but I prefer putting the concrete down and then the liner on top. Will this work? I will put big rocks/boulders on the top shelf and secure them in place with some more concrete, all on top of the liner.

      Any thoughts? Thanks!

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    2. #2
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      I have heard of people doing it, but it seems like a waste both ways. If you are going to use liner, why bother with full concrete, a good collar should be fine. And if you are doing concrete, use re-bar, a good thickness, and an additive such as Xypex to make the concrete very waterproof. Then a liner isn't necessary. Anyway, that's my 2 cents, and worth every penny, lol!
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    3. #3
      EDT is offline Member
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      Quote Originally Posted by BarbJ View Post
      I have heard of people doing it, but it seems like a waste both ways. If you are going to use liner, why bother with full concrete, a good collar should be fine. And if you are doing concrete, use re-bar, a good thickness, and an additive such as Xypex to make the concrete very waterproof. Then a liner isn't necessary. Anyway, that's my 2 cents, and worth every penny, lol!
      My limited space has forced me to keep the dimensions 12ft long x 7 ft wide x 5 feet deep. If I had a bigger area to work with, I would make it much longer, wider and probably 3-4 feet deep. Many people suggested that at 5 feet deep, I risk the walls caving in. I guess I could use a liner and only concrete/rockwork for the first step/collar all the way around the perimeter of the pond. I'd still be worried about the inside of the pond caving in or damaging during Earthquakes (Im in Socal). My contractor whose helping me with the concrete said in order to prevent leaks, he has to apply some sort of sand coating on top of the concrete which isn't expensive but labor intensive. If I could spend under $200 for the liner, it would cost less applying the liner on top of the concrete vs this sand material hes referring to (he doesn't know the exact material name). The guy at the local pond store told me to use Nelsonite Pool and Deck Coating, Speed Cote 2000 paint on top of the concrete to prevent leaks. He also has Pond Shield Epoxy but its $80 per 1.5 quart. which may end up costing more than a liner.

    4. #4
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      You are correct in that if you are doing very vertical walls, just a collar would not be enough. From what I've read, most who do liner over concrete, and will have deep vertical walls, use concrete block with re-bar and concrete in the center of the blocks, for structural soundness. I'm pretty sure that's required building code for earthquake safety.

      I would be concerned about a thin layer of concrete without re-bar in earthquake areas, especially with very vertical 5' walls.
      With block walls, re-bar and concrete filled shell, you get strength, and I believe it would be cheaper than a shotcrete gunite shell.
      Btw, 12'x7'x5' isn't a small pond at all, that's a pretty decent size.

      But I am by no means an expert, I'm sure someone who is more experienced will chime in here soon.
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      EDT is offline Member
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      I was planning on using a mesh/chicken wire for reinforcement along with thin wooden boards for stability and to allow the concrete to grab onto something. Block walls would work too but that would take away 10-12 inches off my pond. I want to maximize size so I don't get the itch to build another anytime soon.

    6. #6
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      For concrete to have strength it requires both reinforcement and thickness. The reinforcement needs to have a couple inches of cover concrete to properly imbed it for protection of the steel and to provide the hinge strength to put the steel in tension in the event of stress or strain. Just putting a couple of inches up is going to just cost you volume, as it is neither thick enough to imbed the steel, or to provide any strength. Typical concrete walls will be 6 to 8 inches thick.
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      I used liner over concrete- actually used 2" foam in between. My pond has vertical walls and is set close to the house and on a hillside; also, in the northern climate I don't trust a concrete pond to not move and open up cracks. Finally, the cost issue. A spray in liner was five times or more the cost of a rubber liner.

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      How thick was your concrete John?

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      Quote Originally Posted by RichToyBox View Post
      For concrete to have strength it requires both reinforcement and thickness. The reinforcement needs to have a couple inches of cover concrete to properly imbed it for protection of the steel and to provide the hinge strength to put the steel in tension in the event of stress or strain. Just putting a couple of inches up is going to just cost you volume, as it is neither thick enough to imbed the steel, or to provide any strength. Typical concrete walls will be 6 to 8 inches thick.
      Thanks Rich, I read a little on your concrete post. Very in depth. Do you think 4 inches of concrete would suffice in keeping the pond strong and standing over 10-15 years? My goal is not to have an impenetrable wall but just to keep the dirt from caving in. Minor cracks overtime are expected, but thats why I want the liner on top. I assume the water pressure will also help in keeping the concrete, rebar/chicken wire and wood in place, but correct me if I'm wrong.

    10. #10
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      why not use 6" thick block with extra bond beams. That way you only lose 2" on each side. I'm struggling also. I live in San Diego and my soil is sand. Great for digging but I'm worried my collar won't be enough. I might go to 4' depth instead of 5

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      rbarn is offline Senior Member
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      There is always polyurea spray in liners too. Or fiberglass lining the pond. Several ways to skin this cat. You don't have frost heave problems in So.Cal so you should not need as strong of concrete shape. Really depends on your soil conditions on whether or not it hold up in the long run. What about earthquakes ?
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    12. #12
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      If the concrete wall is there to provide structural support, I think a minimum of 6 inches, but better at 8. If you are using some form of plywood for a form and are willing to leave the plywood, the concrete could be very thin as a backfill to the plywood. The water would be pushing the wood out against the concrete and soil. The concrete would make a better backfill than soil, being a liquid and flowing and easily compacted, whereas soil is hard to compact. It would normally be thicker at the top than the bottom due to the way excavations go, and that would act as a bond beam to help support the rocks or other edge treatment. Birdman has made some plywood formed ponds in the past.
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      Quote Originally Posted by EDT View Post
      How thick was your concrete John?
      I used 8x8x16 block, dry stack and rebar reinforced with holes filled. You can see details on John's River Pond Construction Thread, which is also good for comic relief in points.

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