Building a rainwater cistern
Water is critical to sustaining life -- either plant or animal. The problem is as populations increase so does the demand for water. Also, droughts or dry seasons make access to water difficult for large segments of the population. One solution for water shortages is to capture and hold rainwater in a cistern. A outdoor cistern is something that a homeowner with enough space and project skills can build at home, but it is a fairly big job so be prepared before you start. Does this Spark an idea?
Instructions
1. Start by digging a hole at least 8 feet deep by 8 feet wide by 12 feet in length. Make it bigger or smaller depending on your water needs. A cistern with these dimensions will hold about 7,500 gallons of water.
2. Form the floor of the cistern similar to the floor of a foundation or sidewalk. Place 2-by-4s at 2-foot intervals with stakes on the outside to form the outside of the cistern floor. The forms should be in a rectangular shape, sitting on the bottom of the hole you have dug out.
3. Start in one corner of the frame and roll out the steel mesh, or chicken wire, to fit in the frame. You may need to roll out several widths to cover the entire frame. Cut the mesh to fit the inside of the frame. Tack the mesh to the middle of the 2-by-4s with a staple gun, so that the mesh is off the ground about 1 to 2 inches. When the concrete is poured have the mesh sit in about the middle of the material to provide support.
4. Pour the concrete floor. This requires quite a bit of concrete so contract with a local supplier to give you enough material. Fill the entire floor form so that the material is slightly higher than the forms. Vibrate the concrete to get rid of any air bubbles with a vibrating machine. Smooth out the material with the concrete trowel.
5. Insert re-bar vertically around the edge of the floor into the wet concrete. These should be about one-foot in length. This provides strength for the walls as well as help hold the walls together with the floor. Allow the material to dry thoroughly. Once dry, remove the outer forms if possible.
6. Build a 2-by-4 framework for the outside of the cistern walls similar to how you would with a conventional stud wall. The studs should be 16 inches apart and the plywood on the inside of the wall should be 3/4-inch thick. Repeat for all four walls. It is very important that you wire the walls together at the corners and provide support with bracing boards so they don't fall outward when the concrete is poured.
7. Build an inside framework similar to the outside framework, only slightly smaller and reversed. Space it about 4 inches inside of the outside framework so when you are finished there is a channel between the two walls, all the way around and about 4 inches wide. This channel is where you pour the concrete and ends up as the walls of the cistern. Position the vertical re-bar in the middle of the channel all the way around. Brace the inside forms before pouring the concrete.
8. Pour the concrete into the forms, by contracting with a local supplier. Slowly fill the forms, going all the way around in layers. Every 6 inches of depth insert re-bar to provide strength throughout the entire form. In the corners, use re-bar bent to a 90-degree angle so that the two walls are connected together. Fill the forms up and use a vibrating tool throughout to remove air bubbles. Finish off the top with the concrete trowel. Insert re-bar vertically into the walls every 2 to 3 feet so that about 3 inches are sticking out of the concrete. Allow the concrete to cure for several days to make sure it is thoroughly dry. Remove the inside and outside form walls.
9. Build a ceiling for the cistern. Form up the ceiling using 2-by-6s, similar to how you would put together ceiling joists. Start by laying out two 2-by-6 boards the width of the cistern. Hold these two boards 3/4 of an inch below the top of the walls inside of the cistern with posts. Fasten 2-by-6 boards between these two boards to form the ceiling of the cistern. Place posts to support the boards that span the ceiling. Be sure the frame is well supported as there is quite a bit of weight sitting on the frame once the concrete is poured. Lay 3/4-inch plywood on top of the 2-by-6 forms and attach using nails, it should be level with the top of the walls. Cover the plywood with a layer of 6 mil plastic sheeting to prevent the concrete from sticking to the plywood.
10. Build a 2-by-4 frame on the top of the cistern walls. The frame should sit just outside of the walls. This is the frame for the ceiling. Repeat the process of laying out wire mesh and attaching to the frame as you did with the floor. Build a 2-foot by 3-foot frame out of 2-by-4s and lay it in the middle of the ceiling frame. Attach it to the plyood with nails so it does not move when you pour the concrete. This small frame serves as a passageway, or door, into the cistern once the concrete has been poured and cured. It is not filled with concrete.
11. Pour concrete into the ceiling frame, by contracting with a local supplier. Follow the same procedure as you did when pouring the floor. Do not pour concrete inside of the small door frame. Allow it to cure thoroughly for several days and then remove the outer frame and passageway frame. Cut a hole in the plywood where the passageway is located so you can get into the cistern. Climb inside and remove the bracing, framework, plywood and plastic from the underside of the cistern ceiling.
12. Seal the inside and outside of the concrete with a liquid concrete sealer. Either paint or spray it onto the concrete. Allow the sealer to dry. Fill in dirt around the outside of the cistern walls and pack it down. Cover the ceiling with a few inches of dirt if you want but leave the passageway clear so you can access the cistern and have an area to get a hose in to fill it with rainwater.
Tags: about inches, cistern walls, concrete poured, inside outside, local supplier, outside cistern, with concrete