Hello everyone,

I'm currently working on a pond project and I'm facing a challenge. My pond is approximately 8x4 meters (26 X 13 feet) in size and almost 2 meters (79 inches) deep at the deepest end, average depth of about 80 centimeters (32 inches). I was planning to use sodium bentonite as a sealant but due to space constraints, the slopes of my pond are steeper than the max recommended 1:3 ratio (V:H) for using sodium bentonite as a sealant.

From what I've read, sodium bentonite is not a good option for me as it tends to creep downwards on steeper slopes. If I were to follow the recommended slope for bentonite, I would have to reduce the depth of my pond to just 67 centimeters (26 inches), which is not good since I live in a region where freezing temperatures are common, thus maintaining a deeper pond is crucial.

I came across a comment on YouTube suggesting to use 10-20% Portland cement mixed with clay or soil as an alternative method to seal ponds with steeper slopes. Has anyone here tried this method?

Please note that I'm not interested in using pond liners, ducks, or pigs for this project. Any other advice or suggestions regarding using natural materials to seal a pond with steep slopes are greatly appreciated!

What would the ducks and pigs do?

Cement of some sort might be your best option for it staying where you put it but you will still have to seal it or add sealer to the cement because its porous (then it is only water resistant, not waterproof). Cement is just a mix of limestone and clay, adding more dirt or clay may make it even more porous. Or it may become so waterlogged, it melts. Also, if you plan to have anything living in your pond, fish or plants, you will have to seal it to keep the alkali in the cement from killing everything (its a pH problem).

I think you will have to build some sort of framework to hold the cement in place like chicken wire and/or rebar.

Let us know what you do. I'm fascinated. I have a clay bottom pond - I have to keep a hose running in it or it goes dry in a day or so.

Thank you for the reply. The pond is dry, I've just finished digging it. I have now been in contact with several distributors of bentonite and all of them say the same thing, sodium bentonite is not a good option for me as it tends to creep downwards on slopes steeper than a 1:3 ratio (V:H). Guess I'll need to look for another solution.

Ducks and pigs can be used to seal ponds.