I am rebuilding a pre-existing Koi pond that came with the house I purchased 3 years ago. The liner was cut off below soil level, and it did not have any filtration.
I am using 2 large food/shipping barrels as my filtration (in addition to a bog) and I am using uniseals to create water-tight junctions between the 4 inch PVC and the barrels. I've used them in the past and they've worked well, but this time they are leaking around the bottom of the barrels when any stress is applied to them. As such, I don't have any confidence in the uniseals holding and I don't want to backfill until I have created robust water-tight joints.
I applied a construction sealant to the joints, both inside and outside and currently they hold water and don't leak, but I want extra insurance. I was thinking of using an expanding foam, like LePage Tite Foam Big Gaps & Cracks, but I don't know how much force the foam could potentially exert and I don't want to destroy the construction sealant seals in the process of foaming it. Another option I thought of is putting bentonite clay around the joints in hopes that if there is ever a leak it will swell to fill the gaps. My only concern is that it can supposedly swell to 30 times its original volume, so I don't want the clay to expand and crush the barrels or rip apart the joints in the process.
With that in mind, how does the bentonite clay work? If I were to deposit ~25 lbs of clay in the area in the photo below to thoroughly surround the joints, if it ever got exposed to water (ground water, rain water from a heavy downpour (mind you this will be 2.5 feet below ground level) or from a leak, does the clay quickly form a watertight shell that expads slightly and prevents the entire mass of clay from getting wet? In that case, there would be minimal expansion and forces on the joints. On the other hand, if the entire mass of clay absorbed water before swelling and becoming impermeable to water, then I imagine it would rip apart the seals. In this second scenario then I would have to apply a very thin layer of clay precisely around the joints and backfill, which would be rather tricky to do I would think.
Is there any other method that's better? Would the clay be better than the expanding foam? Some guidance and information how bentonite clay would react in this scenario would be helpful (I cant find information regarding bentonite clay being used in a scenario like this, mostly I see it being used to waterproof the bottom of ponds). I just really don't want to backfill all this and find out I have a leak in the future and have to dig everything out and hope to find the leak...
