A catalog of non-toxic building systems.
Tuesday, May 17, 2005Pumice-crete - How Volcanos Make A Non-Toxic Home
Pumice -the porous stone made famous by Lava brand soap and notable for its ability to float in water- is a low density basalt produced by volcanoes and is commonly found in most of the world. Related to it are vermiculite -well known to landscapers and gardeners- and zeolite, a form of pumice with the ability to absorb and hold organic molecules and often used in air purifying devices. When combined with common cement mixes pumice produces a soft pourable concrete with much of normal concrete's strength and some very valuable properties. It is self-insulating as it has a foam-like structure and, like zeolite, it retains some ability to absorb and trap organic pollutants. Its rough surface easily takes on any typical plaster, stucco, or adobe finishes and is soft enough to be craved into detail shapes or have channels cut to accommodate utilities conduits. Though commonly used in a variety of supplemental roles in concrete construction, it is recently begun being used as an alternative to adobe for pueblo-style construction and -at least in the US- has become the single-most popular material for housing MCS patients.
Pumice-crete is typically employed with slip-form construction methods commonly used for reinforced concrete construction. However, it is not as strong as conventional concrete and must be employed in thicker walls appromating those of adobe construction. it can be used for roofing; poured over forms, structural beam supports, or made into planks sealed with a thin pour. Typical pumice-crete construction employs pueblo or Mediterranean style design and their contemporary variations, comonly employing viga, rustic beam, or truss supported compound roofing. But it generally has the same potential design freedom as any form of concrete and is foten combined with ferro-cement techniques.
For non-toxic housing it's only disadvantage is a reduced hygroscopicity -though it is better than concrete for this. However, it makes up for this quite well by being cheap, offering better thermal performance than adobe or compressed earth block, much lower labor overhead than either of them, and having some modest ability to actually clean the air inside the home. In fact, some homes have deliberately used zeolite instead of pumice just to maximize this, though zeolite is much rarer and more expensive. Pumice is commonly available in many parts of the US but in others it can be too expensive to import and in those cases foamed concrete may be a better choice. Foamed concretes have many of the same properties and -as long as they use non-toxic foaming agents- are about as good. But some types of foamed concrete -such as Ytong concrete- can only be pre-fabricated in gigantic autoclaves and so are only available as component systems usually limited to trial applications.
Ferro-Cement Construction - From the Industrial to the Fantastic
Invented in the early 20th century, the technique of ferro-cement construction became the basis for some of the most famous architectural works of that century, most notable among them being the fluid organic designs of Antonio Gaudi. A simple but infinitely versatile technique, ferro-cement is based on the use of wire mesh reinforcement to which a fine grained aggregate mix of concrete is applied by hand, trowel, or spray device to form a hard but potentially thin and strong shell. Used both for sculpture and for construction, the technique very often blends the two in fanciful design typified by the free-form organic design movement inspired by the works of the likes of Gaudi. It is a very popular building technique for the more creative DIY home builder and for many Modernist and Post-Modernist designers. It is also a very common building method in countries such as Mexico and in South America and the Caribbean.
As previusly noted, the basic method involves the application of a fine concrete to a wire mesh reinforcement structure. This can be enhanced by incorporating a plastic, foamed cement, or pumice-crete core to the shell structure. A number of pre-made mesh panel products are available such as ICS 3D Panel, Monolithic Panel, and Tridi-Panel. These feature an already installed foam core panel and easy wire-up assembly, saving a great deal of labor. They particularly good for foundation work, simple columns, roofing, and for simple more rectilinear structures. They cannot be bent into very complex shapes or tight curves and so serve better for larger area structural features in true free-form designs, working well in combination with finer mesh for more intricate detail.
Peter Vetsch
Ferro-cement homes are typically based on shell designs using domes, vaults, or complex free-form shapes usually featuring clusters of single-room-per-shell structures or very large area roof shell forms partitioned internally by retrofit structure. Ferro-cement structures can be earth bermed, made underground, or even made to float on water -the same technique having long been used to make hulls for yachts. Labor needs are low, a handful of people being able to produce large structures with few tools -albeit still quite labor and time intensive and demanding a certain artistic talent to produce clean elegant finished. But its greatest attraction lay in the almost unlimited freedom of form possible with these structures and the fantastic fluid forms skilled artists and designers have produced using this.
Finishing work is usually pretty simple and based on simple plaster and stucco finishes or more elaborate combinations of pebble, tile, and sometimes painted finishes. Elastomeric paint is sometimes used for roof surfaces and even the plastic used with pick-up truck bed liners has been applied for truly indestructible exterior finishes. It is common to incorporate a great deal of furniture and fixture elements directly into the forms of the more organic designs, which saves money on furniture but requires more skilled design and present the complication that such features cannot be later changed without selective demolition.
As the basis of non-toxic housing, ferro-cement is a good choice. It's economical, its materials are naturally non-toxic, and its potential for owner-builder construction high. But it is not a hygroscopic material and care must be taken in the ventilation of structures to prevent humidity problems. Also, it's great freedom of form can lead the inexperienced to make costly or dangerous engineering mistakes. Without the support of very talented designers and artists, it is as easy to produce a very ugly looking structure as it is to produce an elegant one, unless one sticks to very simple designs. It is hand-labor intensive, being essentially a sculptural construction process, and there are no readily available contractors for this kind of construction work in the US, even though it has a very large DIY builder following here.
A popular concrete dome home system known as Monolithic Domes uses an interesting pneumatic form variation of the standard ferro-cement techniques. The inflatable dome form is used to support foam and mesh before final cement application and then remains as a protective exterior covering. A similar system design by architect Dante Bini called Mini-Shell may offer an even more efficient alternative. This system deploys its pneumatic form flat and deflated with the rectangular reinforcement mesh placed on top and the cement poured whole over it. After a short partial curing period, the form is inflated under the concrete lifting it into a square-based dome with two or four open arch portals on its side which can be enclosed in windows. Once the shell has set the form can be deflated and moved to make additional shells adjacent to the first, allowing for a spwawling modular structure. Alas, this clever system has only seen use in Europe and Australia and there is no source for it in the US.
Reinforced Concrete Construction - White Mans' Earth
There are several basic forms of reinforced concrete construction used in housing; slip-formed reinforced concrete, prefabricated mdular component systems, and ferro-cement. The oldest among these is probably slip-formed concrete which was employed for homes as far back as the late 19th century. Early in the 20th Century, Thomas Edison actually developed a slip-formed home building system which used huge steel molds to allow homes to be poured complete with Federalist style decorative features. Virually indestructible, a few of Edison's concrete homes can still be found in New Jersey. Later, Frank Lloyd Wright made extensive use of this in housing, devising novel techniques for its finishing including the casting-in-place of decorate stone and the use of hybrid systems based on modular textured tiles called Textile Blocks -a very promising technique that could be revived and improved today. But the use of this for housing really came into its own with the Modernist designers who have seemed to find a grace in this material most others have not.
Typical reinforced concrete construction begins with the erection of cages of steel bar reinforcement which are enclosed in wooden or -increasingly- modular steel forms which hold the wet concrete in place as it cures. All or major portions of a structure are cast at once in a more-or-less continuous pour of liquid concrete allowing for rapid construction. Foundation, walls, and sometimes even roofing can all be made at once.
Often -at least for housing applications- foam panel is applied to the concrete exterior surface for insulation or a foam or sometimes pumice core is cast in place within the concrete. This technique has evolved into a variety of 'insulated form systems' composed of modular plastic foam blocks such as the Rastra Block brand -though such systems are not advisable for non-toxic housing due to a reliance on toxic adhesives to bond the form blocks together.
Due to its very high strength and 'plastic' nature when poured, reinforced concrete is capable of an infinite variety of shapes and decorative styles. But, while ubiquitous for commercial, industrial, and municipal construction, it has had a hard time being embraced for general housing use despite its fairly good economy and exceptional durability. Americans especially have a cultural aversion to the material and for this reason much Modernist architecture has had a hard time being made here or surviving the test of time.
In recent years concrete has developed a somewhat undeserved negative reputation among environmentalists. Most likely a bias derived from their aversion to urban aesthetics where the material predominates, many environmentalists consider it non-sustainable due to the high energy overhead of its manufacture. In fact, all the materials used in concrete are naturally recycled -albeit rather slowly- and there is no reason one cannot use renewable energy to make it. Also, it is the primarily building material for underground homes -probably some of the best kind of housing one can make from an environmental standpoint. However, it's often been mis-used. The term 'white mans' earth' comes from how concrete was regarded by people in Third World countries where its use was imposed by international aid workers, especially in the 1960s. Thinking they were helping raise these countries to a western standard of living, they advocated concrete as a superior alternative to the earthen materials commonly used in indigenous vernacular architecture. But concrete was not readily producable in many of these undeveloped countries so its use made them dependent upon an imported material, encouraging a western style cash economy and the social disruption that brought with it to indigenous cultures.
As a non-toxic building method and material, reinforced concrete is quite practical even though it is not a breathable hygroscopic material like earth or clay. This is often more than made-up for by its increaed strength, it's ability to easily support underground or earth-bermed construction allowing the exploitation of earth thermal mass, and its ubiquitous availability. But because of the common aversion to this material on aesthetic grounds, it is most often completely covered and disguised by other finishing materials supported by the same old light lumber and steel framing of conventinal housing. Affordable non-toxic housing with this material requires embracing its appearance and feel and leaving it unadulterated or simply covered in simple plasters and stucco, hence it tends to work better in concert with Modernist designs.
Modular Ceramic Component Systems - Fireproof Prefab
Almost entirely exclusive to Japan and perhaps to only one or two manufacturers there, modular ceramic component systems have been touted as one of the most sophisticated building technologies at present. The concept builds on mid-century Modernist ideas of modular component housing based on single or multi-room cellular modules prefabricated of concrete and which plug together into nesting complexes to form complete homes. The epitome if this ides is illustrated by Montreal's famous Habitat 67 apartment building, designed by Moshe Safdi and built for the Montreal Expo. A design for a similar system called Habitat Puerto Rico was long on exhibit in model form at Disneyworld's EPCOT Center.
Though the concept saw little use in Western countries -except for municipal/insititutional construction- after the 1970s, in Japan a great many experiments with wuch structures were done. But there too it was generally abandoned for large building only to re-emerge in the form of a system for prefabricated suburban housing. Notorious for the density of habitation, Japan has long had a serious problem with home fires (though, truth be known, the US may have the highest incidence of home fires in the world) and the usual materials and structures with which typical factory-built housing are made are not particularly fire-proof nor earthquake resistant. Thus was devised the notion of factory fabricating large component home modules from solid steel reinforced ceramic and pre-fitting them with utilities, interior/exterior finishes, and built-in fixtures and furnishings. These modules are formed in large steel molds in a factory, fired in huge kilns, outfitted to order on an assembly line, then shipped out on large trucks where they are assembled with cranes, fitted and bolted together, and their module-to-module interconnects linked. Using this system homes widely varying size and design could be assembled in a single day and a few large suburban housing developments were built with these systems. Designed to approximate what is now a standard western-style housing appearance in Japan, the ceramic modules could have their outer surfaced treated for a great variety of finished looks, simulating everything from brick to wood siding with coloring permanently fixed to the material.
Because of its ceramic composition, these building systems could be useful for non-toxic housing but, while they were indeed marketed as more 'hygienic', no particular attempt to exclude latantly toxic interior finishing materials has been made by the manufacturers. So it's an open question how practical these may be as non-toxic housing since such adaptation to exclusively non-toxic finishing materials and furnishings could only be possible with the manufacturers cooperation. Only a few demonstration homes using this system were ever made in the US and the current status of this technology remains unknown to this author.