Cob water tanks

So my idea is to build an aquaponics system mostly out of cob. The fish tanks and the grow beds, maybe even a sump tank if I want one. My question to you guys is, "Will the cob be strong enough to hold all that water?" I'm thinking 16 foot diameter tanks holding about 30 inches of water. That's 3760 gallons of water. Will a circular tank with 1 foot thick walls be sufficient? I will line the inside of the tanks with dura skrim, fish safe super tough plastic sheeting. Thinking of attaching the ends to a board of wood and then burying it in the top of the tank wall. The grow beds will be similarly made, with longer trough like beds for flood and drain. It will be a very humid environment but open to the air. In south Mississippi it's always humid anyway. I would make the foundation very well drained and on a hill top to facilitate the run off to the beds using gravity. I don't see any glaring holes in the idea, do any of you guys?

Hello Michael,

I will do my best to answer your query...

"Will the cob be strong enough to hold all that water?"

That is a very tricky question...

Technically yes...but that only goes as fare as just about anything...including paper...can be "made to work." The real question is this efficient and ergonomically plausible...To that I would have to say very much NO!!

Building vivarium, aquarium and the relate artificial biome for aquatic animal is tricky enough without trying to through a material like clay into it. If all I had was clay, then that is the "ox I plow with," but the effort would probably make me look at other things besides "tanks above grade" and more like small ponds below grade...

I'm thinking 16 foot diameter tanks holding about 30 inches of water. That's 3760 gallons of water. Will a circular tank with 1 foot thick walls be sufficient?

That is pretty much a very large NO! These would need some form of "banding" to resist the volume pressures exerted by the water... Even with 1 meter thick walls there would still be the need of banding and then there is the issue of "proofing" the tanks with a natural material that is "aquatic life safe."

Now...to be supportive of the concept, if you wanted to "slipform" cobb that is one meter minimum against a permanent wood form wall of cypress that is pre built and well "banded" then you may achieve a water proof take that could last. I have seen a few of these many years ago in southern Louisiana.

Hope that answered your questions...

Regards,

j

I would dig my fish pond in the ground, and place grow beds around pond so they waterfall back into pond. Waterfall=DO. Maybe 2/3 buried and 1/3 above ground.And inground pound has insulation for hot and cold,( stops temp swinging around as much), also go deeper than 30 inches. The earth deep down has real constant temperatures. Block sun from pond to minimize algie. It can also make for a real cool kick back spot with waterfalls and fish and plants. I use clay/adobe for my aquaponics, it's cheap(free), but it wreaks havoc on water PH. I live in the Mojave desert so clay is abundant, you can't get away from it. It's in the air, here. But my plants are blowing up. Fish are happy. I have spinache, tomatoes artichokes and strawberries all growing, all producing with a water PH of 8.4. Use the cob go deep, build grow beds around edge of pond power with solar leave space for kicking back in your new microclimate.

Nice, I like the idea of using the fish tank (pond) as the sump. If I use a plastic, fish safe liner the ph shouldn't be as much of a problem correct?

Hello Michael,

The one challenge with "in ground" impoundments for aquaculture is the dependance on pumps to transfer and move water. If there is some reasonable topography to the project site, gravity, and siphon methods, can be put to really good use in draining and transferring water; then more can be done with less pumps. There are "bicycle" style pumps and related hand pumps, yet these are a lot of work, so be prepared.

Now following your original plan (you may have to play with the volume geometry a bit) going down 24 inches may yield enough earth to "berm" the takes to achieve your 30" or perhaps more.

Plastics as liners are considered "transient" and not permanent methods. Even EPDMs have a limited service life span compared to gleying methods for clay/lime based pond sealing methods. Most "fish farming" (organic or otherwise) is done with in ground ponds with clay bottoms and sides. There are countless ancient methods from both Europe and Asia, the latter being the oldest, that formulate gleying methods of animal manure, botanicals/cellulose and/or lime/clay matrix.

gleying methods

Sealing Fish Ponds

I would also note again that wood lined vertical "tanking" or sides is very effective as wood only rots above waterline and not below. Wood lined tanking gives shearer sides to the small ponds (a.k.a rearing pens) there by making the ergonomics and layout of the impoundments more space efficient.

I would also look into the augmentation/amendment to the clays with "hot lime" to create a stronger and more watertight seal to the gleying layers. I can also share that I have had some success in the past making my very first layer within the "dry fresh dig" with 10 layers minimum (30 or more is better) from old newspaper that is then wetted with a "rice soup" or other natural gluing agent. This is always done before ever using a "lining method" and seems to extend the lifespan for linings limited durability. Either way, the "paper layer" goes on first for small ponds and does a lot of good.

Good luck, and post picture please of your project so other can learn from what you are doing!!.....

j