Recently, I’ve been speaking with some of my architecture friends about the prefabricated Ferrocement building system I invented (the am‑cor System), and they’ve said, “Remind me Angus, what exactly is Ferrocement?”
I’ve been breathing all things Ferrocement for years now, and it’s easy to forget that Ferrocement is definitely not mainstream (yet!).
This blog entry will serve as a quick introduction to Ferrocement and my experiences with it. Ferrocement is a construction method, characterized by highly reinforced concrete, formed as thin structural shells. If you’ve never heard of it, I don’t blame you: at Yale Architecture School in the 60’s, I vaguely remember touching on the subject as an eccentric way to create vaults and shapes that were beautiful, but expensive to form; examples include Pier Luigi Nervi’s works.
Does Ferrocement sound similar to our old standby, reinforced concrete? The two are more alike than you’d think: both were invented around the same time & place, in France in the mid to late 19th century.
Ferrocement was initially used for boat hulls, but was eclipsed by the advent of steel hulls, and then largely forgotten. Reinforced concrete went on to worldwide success as a building method, taking the place of slow, heavy, and labor intensive masonry construction (and I mean real masonry as the primary structure, like the Brussels Palace of Justice).
After grad school, I’d occasionally hear about an interesting project using Ferrocement, such as vaulted Mexican market halls by Felix Candela and bridges by Santiago Calatrava, but I always assumed the cost and complication was too great to use in “normal” architecture. It wasn’t until about 25 years after leaving school that I happened upon Ferrocement, during my search for a viable manufacturing system for housing!
I have always been interested in making beautiful and interesting living spaces accessible to everyone in the form of prefabricated & affordable housing. Buckminster Fuller’s concept of the “just add water” factory-made custom house was very appealing to me. My Yale Architecture School Masters thesis featured Harlem remedial housing in the form of interlocking spiral floors with panelized fiberglass walls, to create individualistic apartment units.
After grad school, I worked in New York for a time at some big name firms under famous architects, but eventually I made my way to Jamaica, which was undergoing very fast development. In Kingston, Jamaica, my day job was being the head designer for large developments (something which would have taken me decades to accomplish in NY!). However, my passion was for a low-cost, modular housing system. I tried several different material combinations for manufactured housing: concrete and bagasse board (a derivative of sugar production), steel framing with wood infill, and steel mesh reinforced polyurethane foam. I even built one of my prefabricated houses for Michael Manley, then Prime Minister of Jamaica.
But these material combinations were not durable and secure enough to achieve my goal: a serious answer to the world’s housing problem.
Back in the USA in the 80’s, I kept experimenting with various materials and designs (such as solar & earth-bermed/sheltered homes). I constructed model buildings of such things as foamed glass. I worked with local companies designing homes of foam plastic and galvanized steel. Unfortunately, we found that none of these combinations were strong enough to be safe during disasters, nor durable enough to withstand moisture & mold. Wood & plastics are especially vulnerable to fire, insects, and vermin.
Finally, I discovered the basis for one of my patents: if you coat a standard light gauge galvanized steel stud (the kind you find in office partitions) with highly reinforced cement, it becomes stiff and strong enough to carry the entire load of a building: upper floors, and roofs, no beams or columns required. In order to deform under load, the light weight stud must twist — but the reinforced cement skin keeps it from twisting. So, standard & inexpensive light gauge steel studs can be turned into an extremely robust structural framework.
The problem with my first experiments was that the thin cement coating would crack, if its substrate did not have not the right mix of flexibility, aperture, and surface area. Testing was further complicated by the requirement to observe above and below grade installations over many years, and under disaster-conditions which occur periodically. Also, I consulted with a highly respected cementologist (cement chemist) and developed an additive to make the ferrocement coat more supple and durable.
Ferrocement’s key feature over standard reinforced concrete is that the concrete & steel of the ferrocement stress-skin composite will flex under stress, rather than break, crumble, or delaminate as reinforced concrete does. The way to achieve flexibility is to balance the amount of steel reinforcing with the amount of cement. Although cement is brittle, steel bends rather than breaks. As long as the two materials are keyed together in a composite (interlocking) structure in the correct material quantities, the resulting mixture exhibits properties of both steel and cement: both rigid and supple.
Steel and cement expand and contract at approximately the same rate, and form a bond along their surfaces. Ferrocement’s secret is to increase the surface area between the two materials; the standard round reinforcing bar is not an efficient shape to use for reinforcing, since a circle has the least perimeter for its area.
I experimented with various mesh substrate configurations, and found that expanded metal of certain types interlocks well with cement and provides a lot of surface area for the cement to interact with. In this way I came up with a kind of miniaturized ferrocement glued to a light gage steel frame. I had invented panelized ferrocement! Inexpensive, durable and secure (all steel in the structure is galvanized, as opposed to concrete reinforcing bars), easy to build, totally flexible in design, and with a potentially beautiful cement style surface which can support stone, tile or brick veneer.
With an engineering friend, I patented my panel design, called it “am‑cor”, formed a company to fabricate ferrocement panels, and started building in earnest. We’ve assembled many types and sizes of structures in hurricane, earthquake, and freeze-thaw coastal flooding regions (the climates that are hardest on building exteriors) for over 14 years. The best kind of testing is field testing, and so far we have a perfect track record: no damage or deterioration due to climate earthquakes or the many hurricanes that happen in the regions where our buildings have been built.