By John Fidler, George Wheeler, and Dwayne Fuhlhage
Former United States vice president Al Gore's 2006 documentary film about global warming, An Inconvenient Truth, is credited with raising international public awareness of climate change and reenergizing the environmental movement. The film was a catalyst for political action and helped propel efforts on a broad front. These included initiatives to limit heavy metals and other hazardous materials in the environment, including volatile organic compounds (VOCs), that influence global warming.
It has taken time for the tenets of the U.N. Brundtland Commission (1983–87) to reach a point where most people would embrace its oft-quoted definition that sustainable development should "meet the needs of the present without compromising the ability of future generations to meet their own needs." In that time, the cultural heritage conservation community has come to realize that its work not only adheres to this philosophy but predates it by over 130 years. The preservation and rehabilitation of existing buildings are generally seen as beneficial, not least because the embodied carbon in the buildings is retained and utilized over long time spans. However, not all building conservation is green in the currently understood meaning of the term. There are some uncomfortable truths that we cannot ignore in the hope of being completely aligned with the influential green movement.
So in this paper we try to articulate some of the issues involved, in order to show that environmental concerns are being met in trade-offs—but not in the straightforward ways most people would expect.
The heavy metal white lead carbonate (PbCO3) has been used in artists' and house decorators' paints for many centuries. When white lead is added to linseed oil, the two materials dry together to form a highly flexible adhesive film. Small additions of turpentine and driers make for an extremely successful coating and protection for exterior woodwork. Rather than becoming brittle and cracking, the paint gradually weathers, or chalks away, until the surface has a matte texture that allows for easy recoating in subsequent years. White lead's chalking capability led to its increased use as a fashionable interior paint in the eighteenth century, because of its flat, nongloss appearance. Used as a paste on the internal tenon joint surfaces of window joinery, the lead also limited capillary uptake of moisture at the most sensitive positions in the construction, and thus it doubled as a fungicide, improving durability.
No modern paint can perform as well as lead-based paint in terms of robustness and appearance. Original lead paint applications have saved carbon loads by continuing to function, and by reducing the need for additional carbon to be expended on new paint manufacture and frequent repainting. On the other hand, long-term exposure to white lead is known to be toxic, causing chronic illnesses among lead workers, painters, and children. From the 1970s onward, lead paints were banned in many administrations, or their use was drastically curtailed and regulated.
In September 1989, the European Parliament permitted lead paint use for works of art and historic buildings on the grounds that no other paints were compatible, or as durable, or had the same qualities of appearance; controlled specialist use could continue. The UK government allowed the manufacture and use of lead paint only for the restoration of Grade I and II Listed Buildings and Scheduled Ancient Monuments through a licensing system run by English Heritage and its sister heritage bodies in Scotland and Wales. English Heritage argued that there was no substitute for lead paint; that the continuing lead load on the environment was de minimis compared to other sources; and that less than 8 percent of the listed historic buildings in England (0.32 percent of the total building stock) warranted such special paint finishes. These buildings also tended not to be residential accommodations that might put children at risk.
ETHYL SILICATE STONE CONSOLIDANT
Silicate-based treatments for decaying stonework have been around for nearly 150 years. Ethyl silicates have been used successfully in stone conservation since at least the 1920s. From the 1970s onward, ethyl silicate–based consolidants have become the material of choice of professional conservators. No other consolidants match their low viscosities and surface tensions, the stability of the gel they form with respect to damaging ultraviolet radiation, and their relative effectiveness across stone types. A key feature of their use is the moderately slow gelling reactions that allow the liquid to penetrate decayed stonework and then convert to the stable solid that provides consolidation. However, these gelling reactions produce ethanol, which eventually off-gases. The measured VOCs of most of these consolidants range from 40 to 45 percent (similar to a martini), whereas many regulating agencies impose upper limits in the 10 to 35 percent range. Realistically, ethanol is low in toxicity and in ozone-formation potential compared to many other materials, but regulations treat all VOCs the same.
Although these consolidants have a negative environmental impact, what advantages accrue from their use? First, they extend the lifetimes of heritage materials and their embodied energy. Second, many monuments, sculptures, and buildings are constructed with limestone and marble, which, when exposed to acid rain, themselves give off carbon dioxide. Several ethyl silicate consolidants also act as water repellents, which limit the dissolution of these carbonate materials in acid rain. When evaluating the environmental impact of ethyl silicate stone consolidants, one should consider the volume of material consumed in heritage conservation and consider how that volume compares to other common human activities. Based on industry estimates, without current restrictions the total U.S. national emissions from these consolidants would not even account for 0.05 percent of annual California coatings VOC emissions—less than that from recreational watercraft in the state (which are less regulated).
Adjustments in the formulations of ethyl silicate–based consolidants could achieve a reduction in their VOCs, but only to a degree that may just meet ever-decreasing regulatory limits. Finding a water-based equivalent that meets the performance standards of ethyl silicates may be a better option. In the interim, the best approach is for all parties to participate in the regulatory rule-making process to assure availability of current technology. Heritage stakeholder advocacy can make a difference. In California, joint industry and historic preservation–based education and lobbying efforts (including the intervention of the state historic preservation officer) led to the creation of a stone consolidant category in the state's model VOC rule. This rule set a precedent for regulations in northeastern states and ties into the California Green Building Code, as well as the current iteration of the new International Green Construction Code.
First produced in the 1930s, pentachlorophenol (PCP), C6Cl5HO, is an organochlorine compound used in many industries as a pesticide, disinfectant, and fungicide. The chemical has been one of the most successful treatments against wood decay fungi in damp historic buildings. Compared to the more environmentally friendly fungicides, it is less water soluble and so sustains its fungicidal effect.
However, short-term exposure to large amounts of PCP can cause harm to the liver, kidneys, blood, lungs, nervous system, immune system, and gastrointestinal tract. Long-term cumulative exposure to low levels of PCP is also associated with carcinogenic and neurological effects. General usage is therefore being limited and phased out. Regulators have been concerned about trace evidence remaining, after bans, in water, aquatic organisms, soil, and food.
The European Commission prohibited the marketing and use of pentachlorophenol compounds in a concentration equal to or greater than 0.1 percent by mass in substances and preparations. An exception was given for use in wood preservation for the in situ treatment of buildings of cultural and historic interest, subject to authorization by individual EU member states. The United Kingdom, France, and Spain permitted such uses in licensed forms. Manufacturers of the chemical had until 2006 to either abandon or register continued production. But because there was insufficient continuing construction-industry demand for PCP, it is no longer produced. As a consequence, historic timberwork in ancient buildings risks fungal attack because safer substitute pesticides are less effective, and more ancient fabric has to be replaced.
Despite obvious synergies, historic preservation and sustainability sometimes clash at the level of conservation treatments. But perceived conflicts all depend upon how sustainability is defined. In the three treatment cases cited, the use of potentially harmful materials has been justified for conservation purposes on the grounds that no substitutes replicate their effectiveness. The authentic maintenance and repair of historic buildings and the retention of original physical materials are justified (e.g., through the ICOMOS Nara Document on Authenticity, 1994)¹ and balanced against other risks. These hazardous materials are eliminated from consumer usage and left in the hands of professionals who take precautions against personal and public safety risks and dispose of waste materials responsibly.
This strategy is predicated on sufficient market demand for the materials to be retained in production. In the case of lead carbonate, ongoing production is safeguarded for the time being because the material is extensively used in plastic pipe production. But the lead paint manufacturers are in decline because of commercial pressures, and the survival of this traditional material is not guaranteed.
Heritage authorities argue that uncomfortable as treatment decisions may be, they are necessary for the survival of finite cultural resources. The hazardous loads on the environment are relatively small compared to other emission sources, and the long-lasting treatments save carbon loads by limiting the need to repair and replace materials in the short to medium term. The cost-benefit analysis weighs in their favor, but is an uncomfortable truth.
John Fidler is a staff consultant and the corporate practice leader for preservation technology with Simpson Gumpertz and Heger in Los Angeles; he was previously conservation director of English Heritage. George Wheeler is the director of conservation research in the Historic Preservation program at the Graduate School of Architecture, Planning, and Preservation at Columbia University and a research scientist at the Metropolitan Museum of Art in New York. Dwayne Fuhlhage is the regulatory affairs director with PROSOCO, of Lawrence, Kansas, and he participates in South Coast Air Quality Management District, state, and national VOC regulatory negotiations.