Hello fellow pond enthusiasts,

I'm in the process of constructing a pond and would love to get some advice from those with experience in concrete pond construction. The pond has been excavated, revealing a sloping bedrock at the bottom. The sides are steep, almost vertical, and part of the pond structure is above ground, reinforced externally with a thick layer of soil and stone.

I plan to use concrete blocks for the sides, but I want to maintain the natural slope of the bedrock. To do this, I'll need to create a level base or foundation around the sides on the bedrock before setting the blocks. What would be the best approach for building the foundation? Could a circular slab reinforced with rebar work? What would be the best waterproofing agent or coating to apply to the concrete to prevent water leakage and protect aquatic life from the alkali content of the cement?

I'm aiming for a durable and eco-friendly solution that ensures the health of the pond's ecosystem. Any tips, product recommendations, or construction techniques would be greatly appreciated. I know that it would be easier to just use a pond liner but I am optíng not to.

I just responded in your old thread, but now I see you have gone to Plan B!

Are the sides of the pond also cut down into bedrock, or are they unconsolidated material? Concrete block walls are not great at resisting lateral forces if there is water-saturated, unconsolidated material on the outside of the wall is trying to push into the pond.

Of course, the water in the pond will somewhat help resist the external lateral force. Will your pond usually remain full, or will the water level cycle up and down?

Is there any chance that the bedrock itself could be a seal for your pond? Even if there are natural fractures or a visible joint pattern in the bedrock, sometimes those cracks can be "blind", and not connect to any significant additional void spaces.

Can you drill into the bedrock with a hammer drill and a masonry bit? If so, rebar drilled into the bedrock that also extends up into your concrete pours would make an exceedingly strong foundation.

There are several "construction guys" in the forum. Hopefully some of them also have some expertise in concrete foundations to answer your specific questions.

Good luck on finishing your pond utilizing Plan B!

Thanks for the reply. I could drill into the bedrock. The problem is that it is on a rather steep slope, where at the shallow end it is only about 50 cm (20 inches) deep and at the deepest end it is almost 200 cm (80 inches). The bedrock is a great seal, it doesn't leak any water from there. The problem is the sides that consist of very porous soil. This is one of the reasons why I would prefer not to use a pond liner, it simply wouldn't be necessary for the bottom of the pond. I want to find a method to seal the sides without covering the bedrock.

I have seen some videos where they use shotcrete. I don't know much about it, but it looks like it could be a possible solution.

Look at how they make in-ground swimming pools.

If it was mine, I'd not worry about using the bedrock to be the bottom of the pond, I'd shotcrete the whole thing. I would first plan on somehow putting a drain in the bottom so you can drain it out. to clean it. With no dirt on the sides, and no dirt on the bottom, what you are describing is more like an aquarium. With those steep sides, the fish may not have any place to spawn. Without dirt in the bottom, you will have a hard time getting enough plants and bacteria in the pond to deal with fish waste.

So some type of filtration system may be needed.

If you only shotcrete the soil on the sides, how will you ensure that it is sealed to the bedrock so water doesn't leak out between the shotcrete and the bedrock? There will need to be a sire mesh/rebar structure built on the sides to give support to the shotcrete so it stays in place while it is still wet. Again. similar to how they build in-ground swimming pools.

What happens if the bedrock DOES leak? What's plan B to address that problem?

Im no professional on pools or concrete, come to think of it, I'm not really a professional on almost anything, but I don't think you will have much luck with laying up blocks, I can see very little movement make a block wall crack and leak big time, im like the rest, I would try the shot-crete thing or even a poured wall out of concrete.

And even the shot-crete needs to sprayed against a pretty solid backing to insure integrity and any water sealing properties for any extended period of time, and even more so if you were in an area where there is freezing and thawing going on.
Good Luck!

They're great for entertaining!

Theo, from Hearst Castle?