Robert:
Twenty odd years ago, I had occasion to build a 10,000 gallon cistern using slipform concrete construction with forms from a Ken Kern Owner Builder Book, I can't remember which one. The form was made with two 1/8" x 4' x 3' strips set up with conduit and bolt spacers for a 3" wall thickness. It could be used either for straight walls or circular walls by changing 3/4" plywood templates tabbed to the outside of the steel strips. Mine was for an 8 ft radius. On the cleared site, I dug a post hole in the middle filled with concrete and a pipe nipple to take a 10 ft high center pivot post 1 1/4 inches--anything like that, size not important. A pivot arm 8 ft long with a T is slipped over the center post and pivoted on it and a plywood washer and clamp to support the T, a union on the outer end that mated with a union on the leading edge of the slipform. Drop a 1/4 mile coil of barbed wire down the center pivot post, resting on a plywood disc sitting on top of the T so the barbed wire could be dispensed simply by pulling on it. The center pivot post was guyed from its top to trees outside the building area. A trench was cut for a grade beam footing 10 inches wide, steel reinforced and 16" in diameter, with J-bolts protruding from it. A mortar cart was used to mix a very stiff mortar (a motor-driven mixer will not work). You want a dry mix you can handpack into the slipform that will stand by itself with the slipform is moved ahead. The barbed wire is fed in a single strand into the center of the slipform and buried in 4" of mortar. There is no vertical reinforcing in the wall. One 4" lift today is stacked on the previous day's ring. The form rests on galvanized mortar tabs that keep the form from slipping down the wall. When I got up 8 feet, I plastered a rich cement mix on the whole inside wall and then installed a drain outlet in the center leading to the pump from the bottom of a stainless steel salad bowl for a sediment trap with a foot valve screen for a filter in the line. Then a gravel pad was put down 3-4" thick, black plastic, then 6" wire mesh for slab reinforcement and a 4-6" concrete slab draining towards the collection bowl. The inside was finished off with multiple coats of emulsified asphalt foundation coating. Log joists in a timber deck finished the structure that became the center ring of a 40 ft diameter round house foundation. The 3" concrete wall supported about a third the weight of the whole house and never gave any trouble in the next twenty years. House air was drawn in over the cistern water and the humidity was very welcome in a wood-heated house. When Ken Kern was told about this, he was horified, but 24 years later it's still in good shape. The house structure came in at $6/sq ft built to code, including the cistern which had about $500 worth of materials in the cistern. 10,000 gallons of water in the basement is a great thermal flywheel when you leave a wood heated house for a couple of days in the wintertime. Even after a week of zero degree weather with no fire, there was no ice build-up on the cistern. Signed, Herb Merla's husband
