DIY Building A Brick Cistern To Store Volumes Of Filtered Water
In this example a DIY brick cistern is used to store filtered water. This one holds about 9450 Litres of water. (about 2500 gallons plus or minus 20 gallons) The blocks are filled with concrete and re-enforced with 1/2 inch rebar. They sit on a 5 inch concrete pad re-enforced with 1/2 inch rebar. The blocks are concrete not pumice. The wall is built using mortar mix and standard concrete construction procedures.
It is important to note that concrete blocks are very porous and also that the mortar joints must be water tight. When the walls were finished, a potable water approved water based rubber sealer was applied on the inside. The sealer failed (see the bottom photo). In this part of the country it is too cool and humid for this sealer to work on concrete that is underground.
2011: Cistern with the extra coats of ansi-61 concrete May 2 2011
So far, covering the surface of the walls with cement mixed with #70 sand is the best sealing method for a humid cool climate. I recommend six coats of cement and 2 extra coats at the corners, over the mortar joints and at the bottom where the bricks set on the concrete pad. The total cost for this cistern was under 1200 dollars (not including labor - the largest expense was the concrete and this will vary considerably depending on where you are located - the total cost may run over 1200 dollars.) The cover is galvalume roofing material and the rain water runoff from the cover will be filtered and used in the cistern at a later point in time.
The cistern was filled for the first time starting June 11, 2010.
Water from the slow sand fitters is filling the cistern now: May 5 2011.
Update: June 2010: The rubber sealer failed in early June 2010. There was too much moisture in the concrete, and soil and the humidity was too high and the temperatures too low to allow the coating to cure at the bottom levels of the cistern. The sealer on the top levels of the structure did set up very nicely, and did function as the manufacturer stated. After removing the uncured portion of the rubber sealer, two coats of ansi-61 potable water approved portland cement was applied. This was just the portland cement with no sand added.
The cement was mixed to a paste and applied with a large paint brush. Portand cement cures effectively when it is wet, and will harden under water after it has set up, but two coats was just not enough. At 90 percent full the cistern did appear to be holding the 20,000 pounds of water it was holding at the time. (8.33 pounds per gallon X 2490 gallons = 20,658.4 pounds or about 10 tons) Below are pictures of the resurfaced cistern walls. Regarding the portland cement as a sealer, I would use at least 6 coats - as the cistern has been gradually loosing water after only 3 coats.
(as of August 1, 2010 about 100 gallons had seeped out). I would recommend sealing the outside of the blocks with cement also. Another option is to just put a liner inside the tank, that way if the concrete cracks the liner will still hold the water.
May 5 2011 The extra coats of cement have been applied and allowed to "cure" and the re-filling has started. Each coat was allowed to cure for 24 hours before applying the next coat; keeping the cement moist while it was setting up. The extra coats were allowed to set up for 4 days before starting to fill. The next to last coat was done with 15 percent (by volume) #70 sand added. Two extra coats were added at wall corners and at the bottom where the blocks sit on the concrete pad. Note how the joints between each block are now just barely visible. Each coat of cement took about 1 hour to apply, and about 60 pounds of portland cement and 10 pounds of sand was used for all the extra coats.
Remember thatportland cement (the name does not refer to Portland, Oregon or Portland, Maine by the way) is hydraulic - that is it hardens using water - the chemical reactions that causeportland cement to harden need water to proceed. This coating will just get harder under water. Cement hardens just fine under water. Note that type 2portand cement was used - it is purchased in the bag without sand added - just the cement made by: Ash Grove Cement Company, 11011 Cody Street Suite 125 Overland Park, KS 66210, United States. 913-722-5998. The local supplier of that product is Mutual Materials. The cement is very inexpensive: 12.00 dollars for a 94 pound bag. Most of the cost building this cistern is labor.