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Ferro - Cement

by Ron Davis
www.watermotor.net

Ferro-Cement:  One material for many uses

If you are thinking about building a low-cost, long lasting water tank, a commercial fishing boat, a life-size model dinosaur, a semi-subterranean house,  or a retreat center in the remote desert, ferro-cement might just be your material of choice.

It has been for others. Ferro-cement construction has been used successfully for all of these things.

Other uses for ferro-cement are numerous: walls, floors, and roofs for underground structures,  underground water tanks,  built-in-place well liners, water control devices, canal lining, retaining walls, stairways built over adobe blocks, rain splash protection for adobe and rammed earth structures ---just to name a few.

What is ferro-cement?
   
It is a strong, versitile, low-cost, long-lasting building material made from a wire reinforced mixture of sand, water, and cement. A ferro-cement structure is usually  2-5 cm (3/4"-1 3/4") thick--- much thinner and lighter than poured concrete structures. Because it has wire reinforcing distributed throughout the structure, ferro-cement  structures have much greater tensile strength and flexibility than ordinary concrete.

When building ferro-cement structures the sand/cement mortar is applied to the reinforcing wire with a trowel, never poured like common concrete. Often a form is used to provide the desired shape.

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Why would  builders choose ferro-cement construction over other methods?
 
In the case of the water tank it might be because it is being constructed in a remote location with the  use of  unskilled labor, and where materials must be carried in by hand.  If suitable sand can be obtained locally, then only cement and common chicken wire would have to be brought in.

A conventional poured concrete tank would require several times the volume of materials, as well as boards for the necessary form .

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A ferro-cement hull fishing boat would use materials often easier to obtain locally than wood, and be longer lasting than a wooden hull, especially in tropical conditions.  It would probably be faster to build, and use less specialized labor.

The ferro-cement desert retreat center had the advantages of  utilizing unskilled labor provided by the members of the religious community, locally available materials suitable for desert conditions, and another beside---for religious reasons all structures at the retreat center had to be built in the form of a triangle. (honest!) This last requirement alone might have posed  serious problems if conventional building materials had been used-but posed little difficulty with ferro-cement construction methods and materials.

The model dinosaur had to be made from a low-cost material which could be easily  formed into a complex shape by hand, and would withstand severe outdoor weather conditions for many years.

This illustrates the flexibility of ferro-cement as a building material.
 
In each of these cases ferro-cement presented certain important advantages over other possible construction materials.

Ferro-Cement Basics

The strength of a ferro-cement structure depends on basically two things:

1. The quality of the sand/cement mortar mix.The sand must be clean and sharp.  The cement must be fresh, and the mortar mix "dry"-that is: well mixed using a minimum of water. The mortar should  be used as soon as possible after mixing, especially  in warm
weather.

2.  The quantity of reinforcing material, usually common "chicken wire". More wire results in a stronger structure. A  high quality boat hull will require as many layers of wire as can be gotten into the thickness of the hull.  

On the other hand a water tank or a housing structure may only require two layers of wire in a 2.5 cm (1") thick structure to provide sufficient strength.

I had been impressed 25 years ago when I spent a month  at this retreat center by how well this material had stood up, for decades, in a harsh, desert environment.  The shapes of the structures blend in well with the desert, and the coloring used was "natural".

I recently checked, and found that this center was still functioning after perhaps 50 years. (See "Institute of Mentalphysics" on the Internet, for pictures.)  
 
I had first learned the basics of ferro-cement in India from a fellow building water tanks in rural Nepal, and soon after started building large water tanks myself in California.

These tanks were built around a re-usable cylindrical form made from low-cost wall paneling. The reinforcing wire was attached to the outside of  the form.

I found that ferro-cement  was an inspiring wonderful material for many creative uses-and in  many cases the best material at any price.

Problems
             
There were just two problems when using a form for ferro-cement construction.

One was that since the layers of woven reinforcing wire( chicken wire) were flat, they would lay together against the form, one atop the other.

This made the wire hard to penetrate with a properly dry mortar mix.

And this was also not the best distribution of reinforcing wire for maximum strength. Ideally the wire reinforcing ideally should be located near the  surfaces of the ferro-cement structure.  That is, one layer of wire is against the form, and the other layer near the outside surface.

That means that there needed to be a way of holding the outside layer of wire away from the form while the mortar is being applied. Another problem was the difficulty in knowing how thick  the mortar was being applied to the form. If a uniformly strong, professional looking structure was to be the result, the thickness of the mortar had to be controlled.

Solution:  Wavy Chicken Wire

In order to deal with these problems I  invented a simple material----chicken wire with small waves pressed into it.  This simple material solved all the problems.

I call it Ferro-Form Reinforcing Wire

The  waves can be of different sizes---the adjustable machine I built to produce this material presses waves ranging from 5-20 mm (0 .2 "-0.80 ") in height. The waves are about 33 mm (1.25") apart from crest to crest. 

In an ordinary application a form would have a layer of normal flat woven wire placed over it, a layer of wavy Ferro-Form wire placed over that, and finally another layer of flat chicken wire on top.

The Ferro-Form wire keeps the two layers of flat chicken wire separated, which allows the mortar to penetrate the reinforcing. And it also permits the person applying the mortar to know how thick it is being applied.

Ferro-Form makes ferro-cement construction literally "child's play".

The Ferro-Form machine can be adjusted to produce chicken wire with smaller waves. This allows more wire reinforcing to be used without producing an increase in the overall thickness of the structure.

The patented, hand operated Ferro-Form machine is simple to build using commonly available materials. It will process a roll of ordinary chicken wire in less than five minutes.

Plans for this machine cost $25 per set.  If interested, or have any questions, write to us at cnsorata@ceibo.entelnet.

Ron Davis,
www.watermotor.net

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