Ferro-cement
This is a technique used to build boats, cisterns and swimming pools out of concrete. It works great for a house too.

After doing rockwork and adobe, we couldn’t believe how fast this method was. Plus, it’s extremely strong and durable. The thing we love most though is that you can build the whole building – walls, roof, gutters, cabinets, etc. – out of the same material. We will never do a tin roof again.

It is more expensive than rock or adobe, but still cheaper than a stick-built house, and much stronger (remember the three little pigs!). Another disadvantage is that it doesn’t have the thermal mass of adobe, so insulation becomes a consideration.

What is ferro-cement?
This style of building consists of 2 main stages.

The first is the frame, which is made of metal. You wire rebar, remesh and lathing tightly together. You do not want there to be much slack, as the stucco will fall through. You want it stiff enough so that you can push your trowel, with concrete on it, up against the lathe without it shaking.

A friend of ours, Don, builds everything out of ferro-cement. For his domes, he makes rebar pentagon panels, which all link together to form a geodesic dome. He then stretches lathing over the structure and wires it all together.

With straight walls, we pour concrete posts every 3’-4’, to which we then attach our remesh and lathing panels, which we wire on the ground.

All your electrical wiring and boxes, window and door frames, etc. should be tied to this base frame before you ever mix concrete.

Stage two of the process is stucco, covering the frame with concrete. The wiring is the hard part, as it takes longer and often cuts up your hands; stucco is easy and fast.

Stucco goes on in layers. The first is called a scratch coat, for which the concrete should be a little drier than the subsequent coats. Otherwise, it will just fall through the lathing. It’s called a scratch coat, because you have to scratch it up before the mud sets. This gives the second coat something extra to grip to.

The finishing coats are called brown coats. The stucco needs to be almost runny. It goes on a lot faster than the scratch, and can even be applied with a hopper gun.

There are so many textures and finishes to concrete. Start looking around at stucco and find a style you like, then try and mimic it.

We use a sponge and water to gently texture our walls.

The mix
These are the proportions we use to mix concrete. We mix it in a 5 gallon bucket, using a drill and paddle:

• Put 1 coffee can (1 gallon size) of water in the bucket.
• Add 2 coffee cans of sifted sand (have a third can standing by).
• Add 1 coffee can of cement.
• Add a handful of fly ash (this is not necessary if you cannot find it, but it does make the stucco bind to itself better, as well as having a harder finish).
• Mix with the drill until sloppy.
• Add the third can of sifted sand and mix.
• Add water as needed for the consistency you require.

Stucco
You will need a hawk and trowel, and some kind of scratching device.

• Pour some concrete onto your hawk (it should not be so runny that it runs off the hawk).
• Put the hawk up against the wall you are about stucco, to catch any falling mud.
• With your trowel, push the mud upwards onto the wall.
• With stucco, it is better to start at the top and work your way down. That way the mud has something to cling onto as you are pushing it upwards.

Curing
With concrete, curing is far more important than with adobe. The longer you cure it, the stronger it will be. Don used to cure his concrete for 60 days, until he discovered that he couldn’t cut through it if he wanted to add a window or something. He now cures it for 30 days. We are nowhere near that conscientious. We cure ours for about 5 days.

2-walled stucco
We built our bathroom using this method. It is located on the south side of the house, so we were worried it would heat up too much in summer. To counter this, we built  2 stucco walls and filled in between them with dry adobe dirt.

Another way to counter the insulation problem is perhaps a ceramic, reflective paint, or have porches/eaves that keep it shaded.

Additional Resources:

• Ferrocement Educational Network
• FerroCement.com - Resource for everything ferro-cement
• Flying Concrete - An amazing artistic approach
• Cement Boats - one of the first uses of ferro-cement
• Strawbale/Ferro-Cement - Cement dome with strawblae insulation
• Desert Domes - a full resource for domes, including formulas and calculators