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Thread: why some pond sealants fail

  1. #1
    MCA
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    Honmei MCA's Avatar
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    why some pond sealants fail

    We have seen over the years many instances of where painted/sprayed on sealants have failed and separated from the underlying pond wall and floor structure (block walls, concrete...etc.). Here are just some thoughts on the subject...

    Perhaps the problem is adhesion versus hydrostatic pressure. There may be water in the surrounding ground that is migrating into and through the pond floor and walls trying to migrate into the pond. This is the same basic problem set as in a having a below ground basement.

    The exterior pressure helps the sealant's adhesive strength to give way on the interior pond surfaces. Remember these sealants are designed to have pond water push them into the wall, not external water pushing them into the pond. If I were a sealant maker I would tell you that my products are made to be pushing into the walls and floor....not be in tough of war between two sets of water pressure.

    Water migrating through the walls and floor may case the concrete/mortar surface where the sealant is applied to give way...releasing the sealant. It is not a sealant fault if the substrate erodes.

    It strikes me that if building a concrete and block pond, we need to consider how a good basement is installed. There are waker proofing membranes beneath the floor concrete and usually some type of sealant applied to the outside walls. Also there is a french drain around the floor slab to carry away water....preventing the build up of hydroscopic pressure.

    If we prevent the buildup of water pressure from outside the pond, there should be little reason for a properly applied (follow maker's recommendations) sealant to pull away from the pond wall.


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  2. #2
    Oyagoi yerrag's Avatar
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    This is a very good topic Michael. My pond is built with CHB (concrete hollow blocks), and I'm glad it doesn't leak. A lot of careful attention to details, and some luck was involved. When the plastering was almost finished, days of strong rain created a lot of negative pressure (water pressure from outside the pond) and exposed the weak areas in the mortar. Water marks can easily be seen in the areas of the wall where water can seep thru, exposing these weak areas. When the rain cleared, I had to chisel out these weak spots and applied fresh mortar reinforced with fiber and acrylic emulsion. Without the rain, I would not have discovered these weak spots, and dealing with them later would have been infinitesimally more troublesome. It's too early to tell if my pond would be leak-free long term, but my pound is going on its 3rd year and leaks haven't been problem.

    From this experience, I would recommend simulating a heavy downpour by soaking the pond surroundings with water at some point before the final plaster layer, to expose weak spots, so that repairs can be done, before final plaster layer is applied.

    But I shudder at the thought of applying sealant at the exterior wall of the pond, as we are referring here to ponds that are below grade. It means extra work, involving both digging, and plastering and sealing the external wall. It adds to the costing, even as I understand the truism that the cheapest pond is a well-built pond.

    Because of cost concerns, many if not most ponds are built without external sealants. And my opinion is that there is not much cause for worry not having this safeguard. When a crack materializes, the pressure we should be worrying about is positive pressure, which is pressure exerted by water that is inside the pond. If we have sealant at the internal walls, it should do a pretty good job as the net pressure would be forcing te sealant against the wall because water volume is always greater inside the pond and because of this, the direction of water pressure will be pressing the sealant against the wall, ensuring a seal and preventing a leak.

    This, however, is just my 2 cents and I stand to be corrected on this.

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