A catalog of non-toxic building systems.
Sunday, May 8, 2005Extruded Clay Block Masony - The Industrial Adobe
With the costs of traditional brick masonry becoming untenable in the post-WWII world, many new alternatives to the traditional brick began to emerge in the construction industry. Concrete blocks became the most common but one of the most promising to emerge was the extruded clay block which has become common throughout Europe and the Middle East but which remains -oddly- virtually unknown in the US. Extruded clay blocks are just what their name implies; hollow multi-channel blocks of clay extruded from a machine like toothpaste from a tube and kiln fired to make a hard terra-cotta like material. In addition to blocks, it can be found in a variety of interlocking modular shapes including roofing, wall, and floor panels for both indoor and outdoor use. Loosely related to this are a number of interlocking extruded gysum panels and blocks used primarily for non-load-bearing interior wall applications as an alternative to drywall panels.
Though not as strong as traditional brick or concrete block, the extruded clay block offers some insulation and the breathability and hydroscopic properties of adobe blocks as well as a high precision shape with a diversity of modular forms and a variety of finishes. Their hollow spaces can also be filled with reinforced concrete to make stronger hybrid structures and they can easily accommodate utilities routing by cutting through an outer layer of channels and plastering over them. They they readily take a plaster or stucco finish but are often left unfinished at least on the exterior as the textured surfaces and warm terra-cotta colors are quite attractive as-is.
Used in roughly the same manner as concrete block masonry construction, extruded clay blocks have less compressive strength and so are usually used in a hybrid concrete-filled manner for multi-storey structures (select channels filled with rebar and poured concrete to form a grid of structural reinforcement inside the clay blocks) or as in-fill walls surrounding wooden or steel post and beam structures.
The breathability of the clay block is an increasingly desirable quality today with more health-conscious designers. The blocks provide good insulation while avoiding build-ups of humidity. Like a terra-cotta water jug which chills the water it holds by letting some soak through and evaporate, the permeability of the clay allows for a temperature moderating effect. This is an excellent choice of material for the non-toxic home -assuming one can find these block products and keep the rest of the interior made of non-toxic materials. While large apartment buldings and mass housing developments are built with these in Europe and the Middle East, in the US they seem to be rather rare so availability is a big problem here.
Block/Brick Masonry - Virtue in Urban Tradition
Cities from antiquity to the present have tended to favor masonry construction for the obvious reason that it resists the spread of fire. The very first cities were, of course, built of cob and adobe block and these were the mainstay of urban construction in our civilization until the invention of the fired brick and concrete which became the urban construction mainstays until the very recent emergence of the skyscraper with its heavy steel frame construction.
Fired bricks and concrete blocks were considered an improvement over adobe by virtue of their much higher compression strength, resistance to weathering, and their lack of need for surface finishing. Fired bricks and concrete blocks also had an advantage in terms of production. Their resilience allowed them to be stockpiled in large quantities in the open for indefinite periods of time and they could be transported great distances without damage. Brick offered all the virtues of stone but using materials which were cheaper and more ubiquitous than building grade stone, could be fashioned with less labor, and could be made just about anywhere. But all this came at the cost of breathability, hydroscopic qualities, and thermal mass for which adobe is famous as well as adding a high overhead in energy for their production. These drawbacks, however, seem to have been considered less important in places like the urban industrial regions of the northern hemisphere where traditions of fired brick and concrete use can sometimes be seen to go back even to Roman times. But by the post WWII period the use of fired brick, at least, began to wane worldwide as the cost for the specialized masonry labor steadily increased. Today new true brick construction is rare and expensive and most buildings that appear to have brick composition in fact only have a 'brick-face' facade formed of thin tiles. However, brick construction may be making a comeback in the future -not on Earth but elsewhere in our solar system. Brick construction is considered a logical approach for permanent habitat development on Mars -for the obvious reason that there will be no lumber industry there for quite some time.
Typical brick/block masonry construction is based on the simple laying of blocks with a cement bonding morter between them atop a brick/block or concrete foundation to form systems of load bearing walls and sometimes arches, vaults, and domes. Concrete blocks are often hollow forming an insulated space and a route for utilities conduits. Traditional brick is solid and walls are sometimes fashioned as double-walls with an insulating gap tied at intervals by metal pins for the same effect or, more often today, the interior is framed in wood to host insulation and conduits and finished in the manner of stick framing. Thanks to their high compressive strength, brick/block walls can be much thinner than adobe walls and host heavy timber or steel beams, concrete beams, trusses, or numerous short spaced floor joists in order to support structures of many storeys in height. These can be topped with any kind of roofing, though in the urban setting of the 20th century compound roofing became the most common allowing street-facing facades with elaborate details made by combining brick, stone, metal, and even glass block elements. This masonry technically needs no surface finishing except for appearance since it is quite weather-resistant. But glazed finishes or plaster covered surfaces as well as painted coverings are common.
Conventional brick and concrete block masonry are naturally non-toxic and so make a potentially good choice for the non-toxic home with the caveat that they are non-breathable non-hydroscopic materials. Unfortunately, high and skilled labor overhead make all but concrete block construction cost prohibitive and in the western world it is almost impossible to find contractors who can still build brick homes with traditional methods, using any other interior finishing but wood or light steel framed and sheet-rock covered interior walls. To be truly non-toxic, this kind of masonry construction needs to avoid the need for interior finishing or employ methods similar to that used with adobe or -at the very least- employ traditional lathe-supported plaster walls on certified safe lumber interior framing. The difficulties in doing that have made this a rare option for most non-toxic adapted housing.
One of the most promising concrete block building systems available at present is the DAC-ART Building System which is based on a very sophisticated pre-finished insulated core concrete block that simulates the appearance of natural stone blocks. DAC-ART blocks come in a variety of standard and custom shapes and finishes and go together with great simplicity producing Classical or Palladian inspired structures that need virtually no finishing after assembly. This is potentially very well suited to the employ of pavilion style structures which can link a very minimalist yet Classical looking structure to a Modernist interior design.