Ferro-cement Water Tanks an Affordable DIY Solution

When there is no water there is very little else. That is why water is, with good reason, the backbone of land-based Permaculture design. As designers, we observe and create opportunities to catch and store water. There are many options available to us: in the soil, in biomass and in ponds, dams, and tanks. There is lots of great tried and tested solutions out there that you could explore. Here I will share with you my views on ferro-cement tanks.


 
A ferro-cement tank is, in my experience, an interesting option when you need drinking-quality water but you are on a budget and have a bit of time for a DIY approach. It allows you to obtain a yield of rainwater from the roofs of buildings and store it. 

Ferro-cement was invented around 1840 in France. Ferro-cement structures are created by constructing a frame from thin steel rods (rebar) that is then covered with a metal mesh to create the form of the structure. Then thin layers of sand and cement are plastered over, resulting in a hard, strong finish, ideal for a water tank. Nearly all land-based projects have a need for water storage in tanks and ferro-cement offers a long-term pragmatic solution
 
The advantage of ferro-cement is that it can potentially be applied in many contexts, including remote areas or hard to get to places where other options (pre-cast concrete, metal or large plastic tanks) are unrealistic and more expensive. This is because it is possible in most cases to transport small amounts of cement and some re-bar. Pockets of sand can be found in most soils, taken on a small scale from a river or purchased, making it relatively easy to acquire at low cost.
 
The tanks that I built are used for drinking water, harvested from the metal roof of a house located next to the tank. For catching drinking water use metal or tiled roofs and avoid thatch or wooden shingles. When the tank is finished the roof should be cleaned and a first flush system installed. This redirects the first part of the water coming out of the gutter away from the tank so any debris or leaves do not go to the tank (more about that in the designers manual).


 
As well as channeling rain water directly into your tank, you can also pump water into it. Depending on how the water will be used, different levels of care is needed when harvesting. For good quality water, install a fine screen to stop insects and debris getting into the water, and a cover to stop direct sunlight entering. To make cleaning easy, there needs to be a wash out pipe flush to the bottom of the tank.
 
It is a good idea to position the tank in a place that is shaded and easy to access. To maximise your harvest you can calculate the square meters of your roof and average rainfall in your area. There are several online calculators which make this easy. Then you will know the volume of the tank you can build. The tanks I built (shown in the photos) are 3000 liters and were built in workshops. If you build a tank of 1000 liters, it is still light enough to make it be portable.
 
Everything has its place and decisions are made based on context, climate, project goals and budget. I believe this is a great technique available to people in most circumstances, easy and inexpensive. It is truly versatile and many useful structures can be produced employing this technique from boats to sinks, roofs, and tanks for storing water, greywater filtering systems and aquaponics.
 
Matt Prosser is an international Permaculture designer, teacher, sustainable builder and co-founder of www.holisticprogressiondesigns.com. Matt will be teaching a certified course at the Alisler Yurdu project in Turkey. The course has been designed so participants leave inspired and empowered with practical know how that can be applied anywhere.

Get Your Hands Dirty: Sustainable Building & Permaculture workshop June 23 – 27: http://www.holisticprogressiondesigns.com/turkey-june-2017.html

Alişler Yurdu is is a exciting example of Permaculture and sustainable living in the Mediterranean. Set in a stunning location the project strives to inspire and empower harmonious, healthy and creative lives

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12 thoughts on “Ferro-cement Water Tanks an Affordable DIY Solution

  1. Hi Matt
    Could you please tell me the cement recipe you use for these tanks and are any additives added to ensure they are water tight?

    1. Hey David,

      Concrete base: 3 Sharp sand, 1 Gravel, 1 Cement, 1 Water.
      Ferro cement plaster: 3 Plastering sand, 1 Cement, 1 Water.

      Yes its best to add a waterproof additive, brands vary from place to place.

      All the best!

      Matt

    2. That’s pretty rich concrete. 4:2:1 (gravel: sand: cement) is very common and more than adequate . Only enough water to make it workable. Excess water in the mix makes for weak concrete. After setting up, cement products should be kept as wet as possible for as long as possible. Ready-mix concrete strength is based on 28 days of being kept wet. Concrete strengthening is a hydration reaction and requires water.

  2. Hi Matt,
    We where thinking of doing a tank like that but then we heard that cement turns water acidic. What are your thoughts about that?
    Blessings,
    Manuela

    1. Hello Manuela,
      Water from “the grid” often gets stored in concrete tanks at points in the process of “treating” & transporting. I drank the water from precast concrete tanks & the two Ferrocement tanks I built at the Panya project (Permaculture education center in Thailand) for about four years in total. I never had any problems. My understanding it plastic tanks, especially when exposed to the sun light leak toxins over time.

  3. Concrete block cisterns are another possibility. I have used 4″ x 8″ x 16″ solid concrete block on edge. Alternate 1/2 blocks (4″ x 8″ x 8″) in the first and last courses to stagger the horizontal joints and minimize weak lines to minimize cracking. It goes up like a castle turret. I set the first course on a level circle of brick pieces on a solid gravel base. I pour a monolithic rebar reinforced slab that wraps around the first course. (The highest stress is where the floor meets the wall.) Fill and empty pipe(s) integrated into the floor slab. A couple coats of mortar on the inside. Tightened high tensile wires on the outside (search “gripples”), with spacing between wires increasing as you go up, also covered with a couple coats of mortar. Polyhedral roof of triangles (minimize waste of plywood sheathing). Roll roofing with one panel with hinged door and piece of inner tube to shingle over hinges. Polyethylene lined “ceiling” to reduce condensation on the plywood underside.

  4. Perfect rendering mix Matt. I’ve salvaged many rusted galvanized iron tanks up to 2000 gallons in capacity using this exact render mix. The idea being to plaster the inside of the tank by filling in the corrugations on day one, then apply a second coat over this on day 2, as thick as is practicable and and trowel it smooth. Pour the base on day 3. The outside of the tank looks exactly as it did before concreting and I saw one of my earliest tanks still full of water a good 25 years later!!
    The weak point with the rendered embedded steel and mesh, is that the mesh and steel when embedded in the cement, eventually corrodes and expands, causing cracks and leaks, which is avoided by just having the tank as support for the render whilst it continues to harden over a number of years. I imagine it may be possible to salvage old plastic tanks in the same manner but have not had an opportunity to try this trick. Top quality water comes from cement tanks and I had been drinking this for over a decade happily before relocating.

  5. Ferro-cement has a very high embodied energy and a relatively short life span (c.50 years). Cement absorbs water and iron expands when it rusts and cracks the cement. This seems like a poor choice for a permaculture project.

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