Made in Costa Rica - Fabrication with Love
They have in Costa Rica — and all the rest of the World, for that matter – a perfect solution for all construction and building needs, but incredibly, almost no one knows anything about it. It is especially ideal for the tropics, because it is very cheap, strong, lightweight, cool, waterproof, and so varied in its applications that it can be used for making almost anything you can imagine – boats and oceangoing ships, houses and large buildings, septic tanks and toilets, doghouses, planters and flower pots, swimming pools, hot tubs, fountains and waterfalls, drainage ditches, beautiful tapias and retention walls, solar hot water heaters, walls – the list is endless. You don’t even need to paint it because you can add the color to the mixture.
What is it? Ferrocement!
Ferrocement, as the name implies, is only cement and steel, mixed and applied in a special way. It basically consists of screen mesh or layers of chicken wire covered with special recipe cement that is mixed not according to volume but according to the weight of its ingredients.
Here is a picture of a dome built in Rivas about fifteen years ago that will provide a good opportunity to discuss Ferrocement. First of all the cost of the 35m2 house was about $1,500 including all labor. It is currently rented at ¢50,000 a month, and so has long paid for itself many times over. The shower and the kitchen counter and breakfast nook were also incorporated and included in the price.
Inside, it is always comfortable because of the hoods built into the windows that don’t allow direct sunlight to enter, and the convection roof (little “top hat” on top). The hotter the sun, the more ventilation it creates inside. Also, even though the walls and roof are only about an inch thick, you could easily park a car on top of the house.
Being very strong but flexible, the house is ideal for earthquakes. It is a monolithic construction design, i.e, the floor mesh network is firmly attached to the walls, making it a one-piece house. It would be very difficult to destroy it. Also, the one-piece integrated design baffles the mice, bugs and other bichos who otherwise would be able to find a way to get in.
Here is how it was begun. The main ribs are 3/8” rebar, covered with three layers of 3/8” wire mesh, all carefully wired together with #19 wire using a special drill attachment I made. After the frame was finished, the only thing left was to cover it inside and outside with the cement. I was fortunate enough to be a design student of Bucky Fuller, one of the most important figures in the past century, and much of his teachings are incorporated in the house, although it is not geodesic. Any type of structure can be built with Ferrocement, but Ferrocement offers the chance to get away from plane surfaces and go to curves. If something is curved on one plane, it is seven times stronger than a flat plane. If it is curved on two planes (rounded, like an egg) then it is thirteen times stronger.
The basic formula for Ferrocement is the mesh should weigh approximately half – preferably a little more – of the weight of the cement. The weight of the cement should be a little more than half the weight of the sand, and to use slightly less than half as much water as the weight of the cement.
Ferrocement Formula -Mesh ½ cement -Cement ½+ sand -Water less than ½ cement
When asked “Why do we add sand to cement?” most persons haven’t the vaguest idea. The answer is that the pozolan (silica) of the sand forms a chemical reaction with the calcium carbonate of the cement. Water is necessary for this reaction, but only enough to enable the reaction. Cement does not dry: it hardens. Additives are available as water-reducers and plasticity agents.
Ever wonder why cement here in Costa Rica is so terribly weak? It’s because it is inevitably made as an easy-to-apply soup. The huge quantities of unneeded water take up space in the cement, leaving holes in the cement after it “dries”. Ever wonder why the repairs to cracked cement never last long? Fresh cement poured over “old” cement has only a weak mechanical bond; the chemical bond is lost. The chemical reaction ends after some eight hours (perhaps you have noticed how cement gets warm while it is setting up? Now you know why.)
In Ferrocement, you have to be quick. It’s a one-time deal. No “new” cement over “old”. But done well, it’s well worth the effort: super-strong and waterproof. Cement and steel have almost exactly the same expansion coefficient. From this, I also learned something else: on a steel construction, you can use much less steel using cement. Instead of using a large perlin, for example, you can weld two much smaller ones together then fill them with cement to make a beam that is very strong and solid, with zero “give”. Due to the same thermal expansion coefficient, they can then be welded to form the basic framework for what you are building. You can achieve the same effect with PVC tubing filled with cement: it too becomes very strong.
Well, by now you should have the idea. Should you decide to try Ferrocement, I recommend you start out with smaller projects at first until you are familiar with the formulas and the medium. You could start out with cement-enriched Pegamix at first, and also experiment with color. As you can see, just mixing ochre in the cement will give you a good range of interesting colors. These are planters and window boxes I made while learning myself. They are super-strong and very much superior to the clay and plastic store-bought ones. From this, I graduated on to making a swimming pool for kids, but unfortunately lost the pictures of it.
I am currently working on a design for a “yurt” style of modular living quarters (256 ft2 that can be built using Ferrocement for less than $1,000). But I certainly recommend that persons interested in making drainage ditches, retention walls, houses, furniture… ANYTHING, check out Ferrocement!
Article information source: http://news.co.cr/ferrocement-building-material-costa-rica/3266/
Photos shared by Matt Miller
And then - Oh! What can be done with a little color!