I wrote in a previous blog post how I’m loving earthbag water tanks. My fascination with these water tanks jumped up a notch after reading an article about the difficulties of building a concrete water tank. From what I’ve recently learned by visiting Vanuatu and assisting in water tank design and construction, I know earthbag water tanks are much faster, easier and lower cost to build than concrete tanks.
How earthbag water tanks are an improvement over poured concrete water tanks:
– No need to build forms and strip them off later. The polypropylene tubing serves as the form.
– No mixing (by hand or with mechanical mixer). Crushed limestone can be used by itself as is if it has sufficient moisture to bind together. (Dry powder won’t bind together.) Concrete uses a mix of sand, gravel and cement. In the referenced article (link below) the lady had to shovel the ingredients into a gas powered mixer and then pour the concrete into the forms.
– The wall material (ex: crushed limestone) is handled only once. Shovel the crushed limestone directly into the tubing or put in a bucket and pour it in.
– Lower cost and fewer materials required. While I don’t have a detailed cost breakdown to present here, it’s pretty clear earthbag water tanks cost less. For starters, you could eliminate the expensive wooden roof structure. A ferrocement top could be $1,000 less. Note how earthbags don’t need a foundation and can last for hundreds of years if protected from UV rays.
– Simpler construction process. Read the article and compare what this lady did with simply filling earthbag tubes in a circle with crushed limestone, tamping them solid and then plastering with cement.
– Stronger and more durable. Compacted crushed limestone gets harder and turns into stone over time from what I’ve been told. Earthbags can last for hundreds of years if protected from UV rays. (My earthbag ebook cites a US Department of Transportation study that tested the durability of polypropylene.) Earth berming large tanks like the author did in the Backwoods Home Magazine is highly recommended to counteract the thrust of the water in the tank. What if you have a leak in 10-20 years? Just add another coat of plaster on the inside.
A telling detail about the durability of concrete made with Portland was mentioned in the magazine article. Here’s a quote: “I say “permanent,” but now I have my doubts after overhearing an old timer at the hardware story drawling to another old timer: “There are two kinds of concrete—concrete that’s cracked, and concrete that’s gonna crack.” Then they cackled and wheezed.” So yes, it’s just a matter of time until concrete will bust apart, unless you use ancient Roman type cement or geopolymer.
Interesting fact about cement water tanks: “The calcium content of the cement tank interior neutralizes the acidic rain caught. Water from a ferrocement tank will normally have a neutral pH of 7-8 compared to an acid pH of 3.5 -4 found in other tanks. Acidic water can prematurely corrode surfaces.”
Source: Ferrocement Tanks