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  • Results 1 to 10 of 10

    Thread: Type of underlayment/liner

    1. #1
      Asura91 is offline Junior Member
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      Type of underlayment/liner

      I'm curious as to what the best material for underlayment would be for a new pond. Could I use a vinyl or poly tarp depending on the quality?

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    2. #2
      danzcool is offline Senior Member
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      You really want something thicker. Old school was to use old carpet or carpet underlayment assuming you knew three were none of the tacks left., but it could be anything, I guess even layers of cardboard would be fine, all it is for is to put a layer between the ground and the pond liner so that as it fills, any sharp rocks or roots won't puncture the liner... so for the bottom just sand would also be fine.
      Koiphen member since 05-13-2004

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      aquaholic is offline Supporting Member
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      A lot depends on what your soil is like. Cardboard or carpet would rot out in weeks so hardly any protection against sharp rocks. Sand with dry cement powder mixed in may be a consideration, depending on the steepness of pond walls. The thickness is easy to customise. It sets hard with moisture/time.

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      Most carpet is mainly polyester. I’ve always used old carpet (easily gotten for free) and had a couple of ponds that, years later when torn down, the carpet iwas still intact. In a wet PacNW climate, with a pond that has sloping sides, the area under the pond seems to stay fairy dry. A high water table would change things, plus give you a host of additional problems.
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      danzcool is offline Senior Member
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      even if the underlayment were to rot, it still leaves a layer of rotted material..
      Koiphen member since 05-13-2004

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      Grumpy is offline Senior Member
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      Could I use a vinyl or poly tarp depending on the quality?
      I believe these could work fine in some soil conditions. But for almost all soil conditions I believe carpet is better.

      Engineering design assumes that a load on the surface of undisturbed soil is supported as if that load is applied to the top of a confined soil cone with 45 degree slopes. The soil particles within that cone are assumed to spread the load evenly.

      When we dig a 4-6 feet deep hole, and install a water balloon, we greatly increase the load 4 to 6 feet down on soil that hasn't been exposed to it. This is one reason why a gravel layer in the bottom of the excavation is a good idea because gravel has high friction between particles and will spread out the load rapidly. But gravel will not work for the walls.

      The water balloon is flexible and will continue pushing and seek any weak spots in the floor and walls of the excavation while pulling some liner down into the hole. Your tarp would help spread the load and help the rubber liner in taking some of the tension load. Carpet will do much the same thing to absorb some of the tension load, but in addition it will also provide a thickness of compressible material to spread out the load. Think of the carpet as the difference between shoes and bare feet on wet sand.

      Materials that rot will actually do a poor job. It will initially spread the load, but will soon lose it's strength and thickness. It will create a long term issue that the liner will attempt to fill and the liner will try to pull into the hole more liner to fill the gaps.

      I believe a used short shag carpet is perfect under a rubber liner, but you must be so careful of catching all staples and sharps buried in the pieces. There are photos here of carpets done well.

    7. #7
      BWG is offline Senior Member
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      Carpet that has some natural fibers is still mostly synthetic. Most carpet is 90% plus synthetic. It will hold up long term. I've also used the geotextile material used in landscape construction and sold in big box stores. It's the same product as pond liner but typically less cost.

      I've used carpet instead of geotextile fabric under graveled areas at the farm and as pond liner. Once out of sunlight it definitely holds up.
      Last edited by BWG; 1 Week Ago at 01:51 AM.

    8. #8
      Asura91 is offline Junior Member
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      gotcha, thank you!

    9. #9
      Asura91 is offline Junior Member
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      thanks for the tips, I'll look into carpet for this as well

    10. #10
      Artemis is offline Junior Member
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      We used an inch of sand between the subsoil's fine-grained shale and our liner back in '95. Liner developed some slight holes about 7-8 years ago, and didn't spring a major leak until this year. It was a thicker TetraPond pvc liner, back before you could safely buy EPDM.

      If I had to do a liner in the ground again, I'd definitely make use of old carpet if it were available. Probably along with a geotextile (it's like felt on steroids) and maybe some sand for evening out irregularities. As long as sunlight doesn't touch carpet, the synthetics last a really long time. I've lived in a number of places where, while gardening, I've unearthed old pieces of carpet.

      I don't think I'd want anything waterproof like a PVC sheet between the liner and whatever's below it - seems like water could get trapped in there due to leaking seams/overlap, or infiltration at the top, and make the liner bubble in.

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