Construction of a ferrocement structure begins with an understanding of the material, even a preliminary artistic sketch rests upon the artist's feel for what is possible with a sculptural material.
The components of ferrocement are portland cement, sand, water and reinforcing steel, which is referred to as the armature. All components are purchased at mason supply stores. The mix ratio is three sand and one cement (3 : 1), increase the ratio if the sand is very fine or there are impurities, e.g. 2.5 sand to 1 cement. Locate sand which clean and commonly used by reputable contractors. Do not use lime in ferrocement plaster mix, lime is for laying bricks. Add water until the consistency is such that a line drawn with the index finger slowly settles only slightly. Draw the line on the surface of fresh mortar, make it 2 - 3 centimeters deep. (1" deep). Examine the speed and fluidity of collapse along the line, also known as slump, when delivered by truck; 2" slump may be too stiff, 3" may be too soft, picking this number requires a little practice. Excess water reduces ultimate strength. Add dry materials in measured proportion if too much water has been used.
Ferrocement is a strong composite material usually made from standard cement and reinforcing steel, it predates what is known as Steel Reinforced Concrete, which is simply more concrete mass and less steel than ferrocement. The steel armatures within standard reinforced concrete range from the minimum quality allowed by building codes to modern structural marvels equivalent to ferrocement strength. A masterful steel armature and fully cured concrete are fundamental to ferrocement.
Here's the theory (very brief) : Cement and steel expand and contract with heat and cold at an equal rate. If there is enough steel spreading like capillaries in a human body, forces transmit evenly through the concrete. If force bends the concrete but does not stretch the molecules beyond that of expansion and contraction from temperature change, concrete becomes like rubber. It's that simple.
ferro fact : Concrete does not dry; it cures and becomes strong chemically, in 28 moist days. If concrete dries before this period it will not reach maximum strength. Seven days is okay for a shed, fourteen days is better, go the full twenty eight for a roof in earthquake regions.
Study of early 1900’s structures, bridges and water tanks by historically famous artists, builders and designers reveals ferrocement as an artist’s media that has been applied to large and complicated projects as well as humble human housing; Robert Maillart of Switzerland is one such person, Antonio Gaudà is another. The wire armature inside the sculptural works of ancient masters such as Michelangelo Buonarroti and Leonardo de Vinci are the starting point for understanding the ferrocement structure. The ancient master’s casual swirls of wire sketched the eventual shape in three dimensions and then became the reinforcing armature for a plaster sculpture. These wire sketches were themselves the subject of ancient student art work, some of those student works are now considered so fine and historically interesting they are displayed at major museums. This procedure is illustrated here and reproduced in greater detail in the ferrocement.com sculpture manual.
Beauty inherent in eye pleasing curves is the indicator of structural strength intuitively known and expressed by the fantastic imagining computers in our heads. We often forget that the beauty resulting from calculated curves is a result of mathematical study applied to what art has proven in the past. Robert Maillart, one of the world's best bridge builders, struggled his entire life to overcome the abstract reduction of artistic intuitive knowledge into simple rigidly applied formulae. Interestingly, years after his death, he has come to be considered as an artist rather than one of the worlds greatest pioneering bridge builders; he was the first person to incorporate the road bed of the bridge as structure rather than a simple road bed being supported by the bridge. The great engineer was evidently drawing the bridges as art and using mathematics and simple vector analysis mainly to check and see if the designs would stand. This does not imply he was a mathematical slouch, for it was not until the late 1900's that engineering mathematicians progressed far enough to discover the former engineer was actually an artist.
ferro fact : In the early 1900's, Robert Mailart calculated that ferrocement was economically superior to other building materials for structures of any kind which enclosed greater than 50 m3 (1766 ft3) (13,000 gallons). This calculation remains a good standard today, one century later, perhaps this reveals something subtle and strong about Mr. Mailart's skill with the use of mathematics.
The “how to†aspect of this manual includes how to apply geometric forms as a covering over the area selected to shelter a family, a school, or a hospital. The shape of each structure can be as beautifully different as the variation of shapes between animal species or evening silhouettes of different plant varieties. The old adage, “form follows function,†is perfect for ferrocement. Although it is common to design the exterior structural skin as a public visual presentation and then fit the inner workings into the shell, the sculptural qualities of ferrocement allow the imagination to jump free of appearance until the qualitative structural functions have been fully considered. It is possible to adjust old patterns of thought as part of exploring how to use a sculptural building technique with new and different characteristics. Perhaps you will find that a delicately curved ferrocement shape which fits the seasonal and daily solar arcs is a good substitute for a more massive concrete retaining wall.
Ferrocement structures have several advantages over those constructed of lumber or standard reinforced concrete, strength and flexibility are most obvious. Great strength contributes to the following three: 1) Reduction of maintenance, to almost zero, 2) Reduced need for structural insurance, and 3) Multi-millennia longevity. All three advantages are totally dependent upon good methods and materials. A qualitative advantage is increased design freedom gained by easy use of curvature as well as straight lines. The artistic spontaneity of Javier Senosiain's bioarchitecture illustrates a type of design freedom and zest for life which only ferrocement can provide. Here is his design known as "Tiburón" (shark).
The requirement for good methods and materials becomes quite clear when comparing crumbled concrete bridges throughout the northeastern United States with ancient Roman concrete structures that are still still standing. Safety nets and wood tacked onto the underside of bridges to catch falling chunks of concrete before they harm passing motorists is a common sight in parts of the northeastern U.S., where relatively young bridges have not already been replaced (equally old concrete bridges in harsh climate at the summit of the Sierra Nevada Mountains, in California, are still good). The builder of sculptured ferrocement structures cannot assume materials are of the quality claimed; always test the quality of cement before actually applying it to an armature which has required much time and concentrated effort.
One difficulty with ferrocement housing is the cost of engineering. This cost can be reduced if the builder prepares drawings for professional analysis, that is why this manual begins with the standard building plan presented for building permits from the local government permit agencies. Page one usually includes area and site maps. Hygiene and water source are included also. Smaller sketches may be cut and paste onto large field blueprint paper either by hand with glue or computerized methods, which are also referred to as cut and past. Subsequent blueprint pages are for foundations, utilities, etc. The term, “blueprint,†derives from a description of outmoded printing techniques from the early to mid nineteen hundreds. Many engineers now have modern computer programs which lay a grid of triangles upon a three dimensional drawing and then calculate stresses at discrete points. Good drawings will help this process and save considerable cost in countries with strict permit policy paradigms.
Be aware that there is nothing new here-in. Modern materials are utilized along with techniques as old as mud and wattle; to wit, smear mud on sticks to make whatever structure is needed. Ferrocement has roots in ancient skills and materials and now is joined by a modern companion, fiber reinforced admix cement, space-age mud and wattle. Space-age mud and wattle is one of the most interesting of all building materials because its use is hardwired into our specie; we instinctively know how to build with sticks, fiber and mud.
Sculptural, free-formed ferrocement is usually supported by an internal lattice of steel reinforcing bar, this is the primary technique explored in this manual. Temporary support scaffolding is used for roof areas during construction. Curiosity about supporting structures opens fascinating doors for mathematical study of standardized components that can be assembled to fit any free-form design. Technical design students pondering a fruitful career direction may wish to explore consider this course. I’ve tinkered around with actual supports, digital components and models made with glue and toothpicks and have seen some interesting ideas take shape on horizons that will require more than one lifetime to reach. Very low tech trial and error scaffolding design evolution is definitely possible for the small-scale business.
The last chapter from the organic fiber manual now is part of this manual so ferrocement builders may gain awareness of materials that utilize the exact thinking of the ferrocement armature made of steel and wire reduced to fiber level, this is illustrated at the extreme left axis of the strength graph at the end of this book, a quick inspection of that graph shows that the strength line is tending toward vertical as the fiber spacing becomes smaller.
Working with bamboo, fabrics and fibers is very similar to the support scaffolding referred to previously except that the support system is utilized only once, as a frame for the structure. The bamboo frame is a support during construction which is encased in cement and acrylic soaked fabric to become the supporting mold for construction of hollow tubes, the resulting structural support members are similar to a bicycle frame or hollow sailboat mast fabricated from a composite consisting of cement, a plastic resin admix such as acrylic and fabric such as burlap, muslin, or fiberglass. How to use ferrocement to build a shelter which pays for itself leads to larger concepts which explore how to use the construction knowledge I call space-age mud and wattle to help cure poverty and bring world peace with simple and practical skills.
There are many interwoven subjects involved with shelter and that is why there are several manuals offered for study. So many shelter subjects are so closely related that it is not easy to decide what to include in each manual. Sanitation, for example, has been included while roof rainwater harvest using ferrocement is briefly reproduced here and remains fully covered only in the tank construction field manual.
The concept behind the three chambers illustrated by the septic tank drawing is known as The God Thanker Theorem, in this book. Regardless of the founding theoretician of the three hole system, this basic theorem mandates that an hygienic overview be placed up front in all plan documents. Detailed discussion of the actual construction of a ferrocement septic system is included in chapter eight; this chapter is also published by ferrocement.com in the field manual "Ferrocement Tank Construction."
The scale of the three chambers illustrated is, approximately, L = N + 1.5 meters, where "N" is the number of bedrooms and "L" is the total length of the tank. Circled letters on the trench wall indicate one method of notation for pertinent data or associated project artifacts; geologic information or buried utility crossings, for example. The flat plain presentation morphs to a three dimension schematic to better illustrate the idea of horizontal distance "D" from the drainage pipe to sloping terrain.
ferro fact : Jerry Gottsdanker was the first to grasp that three separate outhouse holes provide enough time between fill-up and fertilizer harvest to make the job enjoyable. He postulated that prior to modern septic science the same idea was known as "The Three Hole System." It was Jerry's system that evolved to satisfy local codes as a water flush septic system. Jeffrey Johnson built a beautiful blue palapa style composting toilet whith a south facing opening for turning the compost which turned out to be a perfect flycatcher because any flies who entered the compost chamber went to the light and did not escape. A version of this fly-catcher, zero flush toilet system is included in the business plan at the end of the glossary.
The first example is a multi-media structure of wood, stone, and ferrocement. It follows the rhythm of the painter’s maxims involving darkest-darks juxtaposed with lightest-lights; here-in translated to sculptural terms as straightest-straights in close proximity with the curviest-curves.
There are at least two structural details to consider in the floor plan below. The small closet near the window in the bedroom is a pillar which supports girders; one spans to the corner pillar that the stairs lead up to, and the second girder is indicated by the dotted line that parallels the A.B.S. waste line anchors to the thick rock stone wall. Steel reinforcement for the closet pillar runs up and out of the foundation under the bedroom slab, which is on top of a two Meter concrete wall, this reinforcement is augmented by a well reinforced concrete floor which acts to spread column weight on a larger area of the corner and might prove worthwhile in a large earthquake.
A major design flaw in the kitchen door became evident during monsoon floods of 1995. The mountain above gave way during two major storms. Both storms released a series of avalanches, the first one broke the door open because there was no door stop to absorb the impact. Banana plants boulders and mud were 40 centimeters deep (16"), it was quite a mess. The door was repositioned to open outward just in time for a second 500 year storm two months later. No debris entered through the door.
The second example begins with a wonderful drawing of a life-time friend, Frank Robinson, now deceased. His floor plan for a purely ferrocement home is curvy, yet, as will be shown subsequently, the structural lines become straight. Though his drawing appears whimsical, Frank was a task-master during actual construction. He somehow managed to be stern with a smiling twinkle in his eye. Compare this rectilinear floor plan and Frank's curved one by turning the page, in the next few pages they will illustrate different methods for placing and contrasting curves with straights.
The foundation plan is trenched and ready for concrete footings. Frank Robinson was a unique architect who was educated as an aeronautical engineer during WWII. He was thus among few architects comfortable with calculations involving curved sheets of composite materials. Frank also used his professional talents to rescue adobe from prejudice and restore it to use in modern architecture. Frank Robinson was a many-faceted, fun-loving man who also helped keep a large neighborhood together as an accomplished master of ceremonies, stand-up comedian and great friend.
The curved white lines are plastic water pipe placed to position reinforcing steel where walls will be. Reinforcing steel verticals are tied to the pipe to hold them in position when the concrete is placed. The white post in the foreground is a temporary power and telephone center during construction. The slightly ragged trench leading from the white post toward the center marks the path of electricity entering the structure. A second utility trench for water and gas enters from upper left.
A steel grid for the floor slab is placed after the trenches have been filled with concrete. The concrete color is so close to soil color it is difficult to see that the slab will sit on well-swept, clean concrete footings. The wooden rails are used as guides to support boards that plane the surface to level. These boards are known in the trades as, screed boards. The reinforcing steel is supported off the ground by small concrete blocks. The finished slab will be 10 centimeters thick with the steel in the center (3.5â€+). Electrical conduits also cross under sand beneath the reinforcing steel.
Notice that a concrete encased steel pipe has replaced the wooden center stake. A pole such as this is very handy throughout ferrocement construction. Five centimeter inside diameter is sufficient in this case (2â€). A support pipe this size is too small for larger projects when walls and roof are done together using a system that the roof plaster is placed first. The construction plan for this home yields finished, full-strength walls before the roof concrete is placed; lateral sway is not present even with tens of tons of fresh plaster and a work crew of twelve, fifteen, or twenty.
Never underestimate the danger of a failed center pole. Imagine yourself four to five meters high, atop a roof 12 - 14 meters wide. Concrete trucks are lined up. Diesel engines are screaming. A large work force is suddenly wide-eyed and frozen. The structure has swayed. If it goes down all will be swallowed by a giant ferrocement amoeba curing harder with each passing minute.
Patient gravity has become a rattlesnake. What would you do? Circa 1980.
“Nobody move!†Point. “You! You’re closest to the edge. Go first! Easy does it; down the ladder.†Nod slowly. Point again, use nose this time. “You’re next. Slide like a snake with a smooth touch of hustle. Down.†One by one. Etc. Sigh. “Okay, partner. It’s you, me, and the money riding on the job. What are we going to do?â€
“How’s this? There’s almost half-a-truckload in the center. Let’s pour spokes which connect with the crew at the walls. Then finish the rest of the roof in a week or so?â€
“Half-meter-wide ferro roof spokes that cure with the walls? Yep. That’ll work.â€
Although the plastic piping shown below was bare at the time of the photo, it was covered with sand prior to placing the concrete.
Ferrocement structures will outlast metal pipe. Metal plumbing is therefore designed to enter through walls above ground level or in plastic pipe sleeves of a larger size. For example, a replaceable two cm copper or steel pipe slides into a 5 cm plastic pipe to reach an inner area unavailable via outside walls. The large white pipe is for secondary moisture drainage.
The concrete slab is usually placed on top of compacted sand. A plastic vapor barrier and insulation add greatly to comfort. Heated concrete slabs are a pleasure in cold climates.
Ferrocement is a quick and easy method to build foundation forms in difficult areas. Such forms are also successfully used to build magnificent supporting girders.
Four different structures have been used as examples thus far. Others will be used to illustrate various construction details.
Here is the finished slab ready for the next construction phase. The slightly curved stand pipe left of the center pole is the septic system vent pipe for the kitchen sink. It rises inside the outer wall before passing through the roof. All utility lines which reach inner positions are complete. Rebar stubs mark wall locations. The drawing on the next page is included to provide visual reference and definition for the photo. Layout of Frank’s design work has been rotated and sized to fit the page.
Reinforcing steel stubs protruding from the finished floor slab are “L†shaped. The bottom of the ell, approximately 15 centimeters long, is tied securely to horizontal steel bars at the bottom of the foundation trench. These bars are elevated and isolated from contact with the ground by small concrete blocks like those previously shown supporting the floor steel grid. Plastic water pipe was used to make curved wall lines for the upright re-bar wall anchor stubs only because it was readily available. Bamboo or thin wood is also suitable for this purpose. Vertical wall anchor steel extends at least 45 - 50 centimeters above top-of-slab.
One might logically wonder about footings which were dug into solid stone for this ferrocement home. Frank Robinson knew quite clearly that the combination of floor, walls and roof add up to such great strength that the foundation was not required as a supporting structural component. He also knew that the cost of a little extra concrete would be less than convincing the local government that a foundation was not needed. His eyes twinkled merrily as he justified the foundation as a way to keep the structure in place during an earthquake. We joked together about mooring the house with chain rather than using a foundation.
I once climbed atop a large boulder and watched waves and ripples swirl in the soil while riding out an earthquake which tipped over a nearby railroad train. The strong earthquake may be less dramatic for a ferrocement structure than a moderate day on the high seas for a ferrocement boat.
The next drawing illustrates the importance of consideration for vent pipe location. I spent over an hour one afternoon looking for the source of sewage odors with my brother, at his home. We eventually determined that the odor came from the vent pipe on his roof. He solved the problem with a long upward extension. Though unsightly, it eliminated malodor. Keep in mind that cool air flows downhill and puddles.
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