The cistern, continued: ferrocement construction

In March I posted about working on our cistern. Since then, I’ve been able to work on it a few more days. My good friend Jon has come over to help in the construction. He’s actually helped with some other projects to and will continue to do so through the summer.

Before the cistern project, I had never attempted the construction of a ferrocement water tank. I first became aware of this type of construction through my dad who found information about it online. It seemed like a neat concept, so I did a little research on it myself. I found a book online that provides instructions. The strength of a ferrocement water tank is provided by a steel armature which is the plastered with a cement sand mixture.

At the time of my last post about the cistern, we had completed the floor framework and poured the concrete for the floor. I was concerned that the floor wasn’t going to set up as it was supposed to. It acted differently than concrete I’ve worked with before. But, it did set up quite nicely. So, construction has continued.

After the floor we began building the walls. The process involved putting welded wire around the perimeter. Then, we added vertical rebar and horizontal rebar. Then, we began framing the roof of the tank.

  The book details the building of a round tank. Because of where I’m building our cistern and the amount of water storage I desired, I decided to build an elongated tank. It is 9 feet wide and 14.5 feet long. I’ve calculated the cistern’s capacity to be 5,300 gallons of water. I changed the plans to suit my application, opting for extra steel in the armature to make sure the strength will be more than sufficient.

For the roof, we bent sections of 1/2 inch rebar that were wired into the frame all the way around. Each of these sections was bent as identically as possible. There will be an opening on top. Rather than make it round, I designed it to mirror the shape of the tank. It will be about 2 feet wide by 8 feet long.

Today we finished installing the rebar in the roof, including horizontal rebar. The next step will be to put another layer of welded wire on the inside of the walls and on the roof. Then, we’ll put on some poultry netting and expanded metal lathe before beginning the plastering process. It’s coming along nicely, but it will still take a few more days of work to complete it.

Work on the cistern

Currently, we are connected to city water, but that’s something that we want to change. It’s been our plan for quite some time, but the municipal water has been convenient. There is a shallow well down the hill on which I have a hand pump and have used for watering livestock. There’s also a spring that flows about 9 months of the year. We also have the pond now. So, there are alternative water sources available.

We also want to cistern rain water that we can catch off of our house roof. In September of 2008, I decided to start constructing a cistern inside the shed portion of our garage. The garage is a pole building that has an original area of about 24 feet by 40 feet. The previous owner built the garage and also added some space on one side that is about 12 feet by 40 feet. We used this shed portion as a goat/chicken barn for a few years. With gutters we should be able to harvest quite a bit of water off of the roof. Additionally, locating a cistern here would allow us to let gravity provide water pressure to our new house, because there is about a 50 to 60 foot elevation change between the two.

It is inside the shed that I began the construction of a ferro-cement cistern. The basic idea for ferro-cement construction is to build a metal framework that provides strength and structure. This framework is then plastered with a cement-sand mixture that makes it so it will hold water.

The first thing to do was to provide a level space for building the cistern. I used hand tools: a shovel and a grub hoe mainly. I hauled the material that I dug out outside and dumped it on the hill behind the garage.

The next order of business was to begin building the metal framework. This consists of welded wire (re-mesh) and reinforcement bars (re-bar) that are wired together. Essentially, you create a sandwich with the re-mesh on either side of the re-bar all rigidly tied together. Here are two photos of the work I completed in September 2008:



Sadly, after getting started on the framework, I did not get back to the construction of the cistern until Tuesday and Wednesday of this week. We decided about two weeks ago that we should go ahead and get the cistern constructed and start using it sooner rather than later. So, I enlisted the help of a good friend who came over this week to help me.

The first day we worked on finishing the metal framework for the floor. We had to add another layer of re-mesh and a layer of chicken wire on top. Wiring all the layers together takes time and quite a bit of wire. The end result is a framework that is strongly joined together and that will make for a strong cistern. The different layers are offset from one another so that the spaces between the wires and re-bar become smaller and smaller.

The following two photos show the floor ready for to be poured:



We finished the framework on Tuesday after a full day of work. On Wednesday we began with the concrete. I bought an electric concrete mixer for this project and later projects, including plastering the straw bales on our new house this summer. I already had sand and bags of cement that I had bought in 2008 for the cistern project. The sand was fine, but the cement had absorbed some humidity.

We carried the concrete mix into the shed in buckets and used trowels to force it into the framework. We had to build it up at the edges to the point that the walls would later extend from. I also put in a drain line and an outlet pipe. It took a full day, but we got the concrete finished for the floor (sorry about the dust spots on the camera lens).

At this point in time, I’m not sure that the concrete is going to set up hard enough. I think the cement didn’t work properly, probably from having absorbed moisture during the last year and a half. At first, it seemed like we had nothing more than wet sand, but it is hardening somewhat. I just don’t know if I will be able to trust it for completing the cistern. The dimensions I designed for the cistern would provide about 5,000 gallons of water storage. That’s a lot of weight and pressure.

Our current thinking while we wait on the floor to cure completely, is that we may put in two 2,000 gallon poly water tanks. They will sit on this floor with no problem. I can add some wire around them which will attach to the stub wall that is already framed. Then, inside this wire, I can insulate around the poly tanks with sawdust or some other material. We are not sure yet which way we will proceed. The poly tanks would cost a bit more, but they would save a lot of time and labor. We’ll decide for sure in the coming days.