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First, I'm open to alternatives and creative solutions, so the simple form of the question is, "Can I use bentonite as a lining for a normal (chlorinated) swimming pool?" But, in case there are other solutions, I'm describing the situation.

I have an old barn about 300' behind my house, in a wooded area. I'm going to be renovating the barn. Near it is a lagoon, about 200' long by 25-30' wide. I'm thinking of using the end of the lagoon that's near the barn as a swimming pool. This is in the middle of the woods. Even though we're going to have to clear the area around the pool and barn to some extent, we want it to look as natural and pleasant as possible. (I do not want to use vinyl liners or anything like that. Everything I read about them indicates they have to be replaced in under 10 years.)

Another issue is that this is a remote area, 1/2 a mile off the road, with several turns and the need to go over a creek crossing. I'm not sure a truck carrying a fiberglass pool could make it back there and successfully unload a swimming pool form and place it properly.

I've been researching to learn about pools that use chlorine or salt water (and I know the salt water pools use chlorine from the salt), as well as natural pools. I'm still trying to decide whether to go with a chlorinated pool or a natural pool. While reading about natural pools, I see one good solution for lining the bottom is to use 3-4" of bentonite clay.

What I find frustrating is I don't find details on this anywhere. I don't know if the clay hardens into a firm surface when tamped down and when water is over it, or if it's still slightly porous and still allows water to leak through it. I also have no idea if the bentonite would interact with chlorine if I use it to line a chlorinated pool.

I have several reasons why, if I make a chlorinated pool, I want to use bentonite. Naturally, I'm aware that it'll cost less than fiberglass or concrete. But I also want the sides to slope down, from ground level, and into the pond, to give it a beach like feel. Bentonite is also white (or white-ish), so it can look a bit like a sandy bottom. While I could do slopes like that with concrete (which is the most expensive option), I can't do that with fiberglass. (And I can't make a custom shape with fiberglass, either.)

With what I have learned, bentonite seems my best choice for a liner, but I don't know yet if I'll be making a natural pool or a chlorinated one and I'm open to suggestions for alternatives for lining the pool.

So can I use bentonite for lining a chlorinated pool? And are there other suggestions, given the situation I've described, that might work better?

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Bentonite clay at the bottom of a pond does not form a hard surface that could be walked on. The clay layer will be a goo which is virtually impenetrable to water, but absolutely unsuitable for walking on. If you were going to do this, I think you would have to have a layer of sand or gravel on top of the bentonite layer.

How common is a "natural" swimming pool where you are? Have you researched how to prevent the growth of the amoeba Naegleria fowleri? https://www.mayoclinic.org/diseases-conditions/naegleria-infection/symptoms-causes/syc-20375470

  • As best I can tell, natural pools aren't used much around here at all. I know they're big in Europe, but I can't find much useful info. At this point, I've been seriously thinking of bentonite for the liner, then using chlorine as one would in a normal pool. I know there are issues with various parasites and diseases, but considering that I've spent many years swimming in lakes and rivers (and preferring them over ponds), I figure a natural pool would be safer. A layer of sand or gravel would be fine - no problem there. My concern is if bentonite interacts with chlorine. – Tango Nov 2 '18 at 18:44
  • If the soil around the barn are contaminated with the feces of domesticated animals, this would not be a good place for a swimming pool. – Jim Stewart Nov 2 '18 at 19:20
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    Yes, that’s a good point and I’ve discussed that at length with the state DEQ (Department of Environmental Quality) nad with many others. Basically it has not been used since the early 1990s, over 25 years ago. The septic area was dredged out by the previous owner and I’ll be dredging it again. The short answer, from anyone with the biological or environmental background is that it’s been so long that it’s not an issue. Everything would have degraded long ago. – Tango Nov 2 '18 at 21:03

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