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Somewhat like processed food, processed building materials are liable to be less healthy for us and for the planet than natural ones. So what should we be watching out for with these types of materials? There are three main concerns. The first is that many of the processes are themselves energy-intensive and polluting. The second is that of industrialization itself: its tendency to become centralized and geared to quantity production often leaves in its wake a correspondingly large amount of damage to the environment. The third concern is the sheer number of new synthetic chemicals that new technologies have allowed us to produce, particularly the organic petrochemicals. Some of these are relatively harmless, but others are highly toxic and often used unnecessarily as a substitute for natural products.
Entirely new materials are being produced every day. We can't turn the clock back and disinvent them; however, in certain cases, we can wake up to their effects and if necessary ban or restrict their use.
The processes in this section are dealt with under three headings:
• Processing earth and rock
• Metal production
Synthesizing chemicals from coal, oil, and gas
PROCESSING EARTH and ROCK
The various methods of processing earth and rock to produce bricks, plasters, cements, and glass are among the oldest known human technologies. They vary greatly in the damage they can cause to the environment.
Bricks and Tiles
Bricks were first produced in a sun-baked version 6,000 years ago, making them perhaps the oldest processed building material. Since that time there have been many developments in fired-earth technology, and the same processes have been used to develop a whole range of components. In addition to brick there are floor tiles, wall tiles, roof tiles, firebricks, and drain- pipes of many different colors, properties, and strengths, all of which have been developed from the same basic raw materials. Western Europe has made more use of this technology than any other region of the world.
In terms of aesthetics, handmade bricks and tiles have a marvelous individuality of texture and character, ranging in color through many shades of red, brown, yellow, grey, and blue. It is the different firing methods, as well as the different constituents, that produce bricks of varying textures, colors, and strengths. Most of these components have been developed to a size that can be handled by one person.
To understand the ecological impact of these manufacturing processes, it is worth examining them in more detail. The raw materials come from three basic sources:
• Surface clays—typically from river and glacial deposits
• Shale clays—usually from surface outcrops
• Fire clays—often found deep underground beneath coal seams and so requiring mining (used only for special heat-resistant bricks)
The different materials are blended to obtain the desired characteristics. Crushing and pounding of the harder materials such as the shales is usually necessary in order to provide a uniform consistency. There are also various other ingredients that are sometimes added, including calcium silicate sand and lime.
Before firing, water needs to be driven off through drying. Firing takes place at a temperature between 1,600° and 2,000°C (2,900° and 3,600°F), depending on the type of clay used. This is the point at which most environmental damage can be done. At present, kilns waste considerable quantities of heat because of the way the firing is carried out. This can be reduced by increasing the insulation and incorporating heat-recovery techniques into the kilns. In addition, during firing toxic gases and vapors that are both corrosive and polluting are often produced, again depending on the raw materials used. This pollution can be reduced by choosing different raw materials as some manufacturers are now doing.
If we require bricks for renovation, we should support those companies that are doing the most to overcome these environmental problems. Companies concerned with ecological issues will also need to ensure that their extraction methods are not unduly destructive of habitats and that water tables are not adversely affected.
Lime is the basis of many building materials such as cement, plaster, and certain types of bricks. It is used in steelmaking, in agriculture, for water treatment, and in innumerable industrial processes. It is also a constituent of paints and many industrial finishes. It is even used in scrubbing flue gas emissions of sulfur dioxide from power station smokestacks.
The actual manufacturing process that produces lime is a simple one. Limestone, chalk, or shell deposits are heated in a kiln to a high temperature until carbon dioxide is given off, producing a material known as quick lime. This quicklime is then combined with water to produce slaked lime, which is the main constituent of lime plasters, lime mortar, and lime washes. It gradually hardens over a period of time as it reabsorbs carbon dioxide from the atmosphere.
If we look at the overall ecological damage that is done through the production and use of lime, it is mainly the quantity of the material being extracted that is the biggest threat, since it is used in so many ways (see LIMESTONE). If we do not ensure that current policies are changed, then whole landscapes in areas of outstanding natural beauty are likely to be leveled. We therefore need to consider carefully our use of lime-based building materials, particularly those that use large quantities of lime in their manufacture.
There are three different types of plaster:
• Lime-based plasters
• Gypsum-based plasters
• Cement-based plasters
Cement plasters are the strongest and also the most water-resistant, and for this reason are chosen for external stuccoing of houses. Although other plasters can be used externally, they need to be coated first with a layer of protective paint.
Gypsum is now the common basis for all modern interior plasters. Gypsum (calcium sulfate) is found naturally, but is also produced artificially. Its main source is from natural deposits, which are mined in a similar fashion to limestone. In order to manufacture gypsum plaster, it is necessary to drive off some of the combined water in the gypsum. it is then ground to a powder. When mixed with water it recombines and sets relatively quickly. Calcium sulfate is now also produced as a by-product of scrubbing the sulfur dioxide out of power station emissions. This source of calcium sulfate is now being used to supplement natural mined gypsum. The environmental problems that accompany the use of gypsum plasters are similar to those of any material that is extracted from the ground. However, we have not yet seen the same severe problems of ubiquitous use that have occurred with mined and processed limestone.
The Romans used a type of slow-setting cement that they made from volcanic ash and lime; it was this type that was used until Portland cement was developed in the 18th century. Cement is a complex mixture of materials: there are many different blends, each with its own given name. In its simplest form, lime and clay are mixed together and heated in an oven. The resulting mixture is then ground to form a powder which, on combining with water, sets to a hard and durable material; this powder forms the basis of cement mortar and concrete. Raw materials for modern cements use silica, alumina, and iron oxides, and different compounds of calcium, including gypsum.
There are a number of environmental problems associated with the production of cement. The very high temperatures (1,3000 to 1,500°C, or 2,400° to 2,700°F) that are needed to burn the mixture require a large energy expenditure, and the gases and vapors that are given off in the process contain metals and oxides of sulfur. The chromates in cement are considered particularly dangerous. There are two other hazards to be aware of in using cement: breathing in the cement particles can cause silicosis of the lungs, and contact with wet cement can burn the skin.
Cement-making is yet another industry that uses limestone, but energy expenditure and pollution pose by far the biggest problem. Fortunately, there is much scope for developing a “greener” cement.
Glass is certainly the most environmentally useful of the processed materials: its properties of being durable, transparent to light, and reflective of infrared radiation give it the ability to trap sunlight in way that no other material can do. Being almost totally inert, it is a healthy material both to have as part of a home and also for food and drink containers. It can easily be washed and reused or recycled by melting down.
The oldest glass ever found was made in Egypt around 2500 BC. The Romans developed the technology and produced the first crude glass blowing. The Venetians rediscovered these techniques and developed them so that glass became available all over Europe. The Industrial Revolution saw the advent of large-scale production and the development of drawn and plate glass.
What most people do not realize is that many substances can be used to form glass. The most widely used is silica (quartz-sand). Lime and sodium or potassium salts can be added to improve workability. These materials are fired at a temperature of 1,500° to 1,60O°C to 2,900°F), at which point the glass is as fluid as water. There are three basic ways that glass is
• Vertical drawing—producing drawn glass
• Flat sheet casting and rolling—producing patterned glass
• Floating on molten metal—producing float glass
Many different compounds can be added to the glass to give it different properties or colors. Lead silicate produces glass with a high refractive index (such as high-quality crystalware), and colored glass is made by adding metals such as copper, nickel, or cobalt to the melt.
Both sand and limestone are required for the making of glass, as is a large amount of energy Owing to the detrimental ecological impact of its production, it is important that it be used as efficiently as possible. Glass has the added hazard that there is a danger of cuts from falling into it or through it; however, it can be made exceptionally strong by either laminating layers of glass together or toughening it by heat treatment. Safety glass is up to five times stronger than regular glass and , if broken, disintegrates into harmless fragments.
There are also various coatings that can be used to produce certain effects. Solar control glass is tinted to reduce glare and heat gain; and low emissivity (low-E) glass reflects heat back into the home, contributing to energy conservation.
Besides flat glass, there are two insulating materials made from glass that are also relevant for energy saving:
Glass fiber is used as an insulating material and reinforcement, and is made by blowing molten glass out of holes in a fast- spinning drum, similar to how spun sugar (cotton candy) is made. When made into quilts or batts, the bonding agent used is usually urea-formaldehyde resin. A similar process is used for making mineral wool, in which case molten rock is used instead of molten glass. Slagwool is the best of all such products, environmentally speaking, because it is a by-product, and thus no new material has to be specially mined to manufacture it. It can also be spun directly from the furnace, thus saving energy.
Foam glass is just what its name implies, but it is not commonly used because of its high cost. However, it is extremely durable and water-resistant; this combination makes it relevant when considering the insulation of basements or underground buildings where there is the likelihood of the material remaining wet.
Coating fired clay products with a glaze (glass) is a method of preservation and decoration that is used for ceramic tiles, glazed tiles, glazed fire clay, vitreous china, and vitreous enamels. Ceramic products, although having a high embodied energy, are generally ecological in that, for the most part, they are extremely durable and can often be recycled. This recycling is facilitated if care is taken to fix them in the first place without too strong a bond.
Most metals are environmentally destructive in their extraction. They also tend to be highly energy-intensive and polluting in their production, yet There are considerable differences in their damaging effects. We need to look carefully at the damage the extraction and production of these metals can do, and then decide which metals should be avoided altogether and which limited in use as far as possible.
Of course, there are some uses for metals for which there is no substitute, such as electrical and certain plumbing items, and fixings such as screws and nails. There are a number of metals that are now scarce, such as lead, tin, tungsten, and zinc. However, they are also poisonous, so perhaps their reduced usage will be a blessing in disguise. Most metals are in fact toxic, including mercury, nickel, zinc, aluminum, silver, cobalt, cadmium, titanium, selenium, and chromium. In general, the heavier the metal on the atomic scale, the more toxic it is likely to be. The exception is gold, which is stable and inert and thus harmless.
The most widely used metals in building are steel, copper, aluminum, and lead, and these are dealt with next in a little more detail.
Iron and Steel
The raw materials for the production of iron are: iron ore (mainly oxides of iron), coke or charcoal, and limestone. “Pig iron” is made by heating these materials together in a blast furnace. Steel is made by reheating the pig iron to purify it, then adding various materials to make different types of steel. Carbon is the critical ingredient which distinguishes steel from iron. Manganese, silicon, and phosphorus are also added to give various proper ties to the finished steel. Other alloys of iron include nickel, chromium, vanadium, tungsten, cobalt, etc., which are used to produce stainless steel and especially strong steels or hard steels. From a domestic perspective, the most important of these alloys after steel is stainless steel, which contains 12% to 18% chromium and some nickel.
The main ecological effects of iron and steel production involve the huge quantities of raw materials that are used and the energy consumed in the process. Perhaps the most damaging effect at present on a global scale is the destruction of vast areas of tropical rainforest, which are being destroyed to produce charcoal for pig iron production in Brazil. More than 50% of this pig iron is being exported to other nations so that Brazil can repay the continuing interest on its foreign debts.
Copper is one of the few metals found in a free metallic state in nature, which accounts for its early use (around 8000 BC). Other metals in the same group are silver and gold. The raw materials for copper production are copper ores (mainly sulfides), native copper (its free state), or ores mixed with other ores of nickel, zinc, or lead.
Processing consists of three stages:
1. The copper ore first has to be separated out by grinding the different ores into a fine powder and mixing with water and reagents. This mixture is then violently agitated to produce a heavy froth, which contains 95% of the copper ore.
2. After settling and drying, the resulting material is roasted to remove further impurities, including sulfur dioxide. This stage is the most polluting, producing the major ecological problem associated with this method of processing. Smelting reduces the large quantities of sulfur dioxide otherwise emitted.
3. Electrolytic methods are used for further refining.
At present, each stage of the process is environmentally destructive in some way, whether it is the large amounts of water that are used or the sulfur dioxide that is released into the atmosphere from the sulfide ores.
Aluminum is the most abundant metal element in the earth’s crust, but is surprisingly difficult to separate from its mineral compounds. It has there fore been a relative newcomer as a refined metal; it was not produced until 1827. The raw materials for its production are bauxite, which is rock containing about 50% aluminum oxide, sodium carbonate, and limestone. The refining process is complicated, lengthy, and highly energy-consuming. Smelting involves the aluminum oxide being reduced, using carbon heated in an electrolytic bath. Aluminum refining is the most energy-intensive process known for producing materials used in the construction industry, being dependent on electricity and requiring approximately 126 times the energy used for timber production. In its favor, though, aluminum is easily recycled, corrosion-resistant, and lightweight.
Lead is a highly toxic metal, as are its soluble compounds. Its use in the building industry is being steadily reduced for this reason. Once widely used as the main material for channeling water, whether on roofs or in gutters, downpipes, and all internal pipework, it is being replaced mainly by copper and plastic. Lead is still a useful material in roofing; however, if rainwater is to be collected from a lead roof or lead guttering for use in the garden, then it would be wise to use this rainwater only on areas producing non-edible produce.
The production of lead is similar to that of copper. Galena (lead sulfide), which contains up to 86.6% lead, is the main raw material. However, lead also occurs dispersed with other minerals; the refining processes can be very complex, the aim being to recover traces of silver and gold along with other impurities such as arsenic, zinc, and tin.
Most other metals that are used in building are used as alloys or as pigments for plastics and paints.
The following metals are particularly toxic:
All these metals should be avoided wherever possible. Chromium is perhaps the most difficult metal to avoid, since it is so much a part of existing kitchens and bathrooms, which often contain stainless steel sinks and chrome-plated fittings. Plating uses a small amount of the metal and adds durability. Cadmium is often used in batteries, and these should be avoided where possible. If this proves impossible, used batteries containing heavy toxic metals should be treated as a toxic waste and disposed of properly. Titanium is a metal that is being increasingly used in paint manufacture as a substitute for lead. However, it is a difficult metal to extract, and we should limit its use to essential requirements.
CHEMICALS FROM COAL and OIL
The third category of chemicals are those that result from the processing and synthesis of coal and oil. These form the constituents of a huge number of manufactured products.
Coke and Its By-Products
When coke is produced from coal, all the volatile compounds are driven off, and these condense as coal tar, a mixture of hundreds of different compounds. This coal tar is then refined into chemicals of different volatility through the process of distillation. From these chemicals a vast array of dyes, drugs, perfumes, explosives, antiseptics, plastics, resins, pesticides, synthetic fibers, solvents, and other products are produced. From this enormous range of chemicals, the building industry makes use of those that can be used for waterproofing (pitch) and timber treatment (creosote), as well as plastics and paints.
Apart from any environmental costs resulting from extraction, the environmental damage due to coke works and liquefaction refineries depends entirely on how well the production is run. There is no need for chemicals to leak into the atmosphere or local water supply, though in practice this often occurs. What is perhaps the most damaging result for the environment is that many of these synthesized chemicals are produced as by-products, which are then marketed as something that we need! Though many of them may be genuinely useful, a number are used only because it is cheaper to find a use for them than to dispose of them. We have little idea at present how many toxic chemicals have been foisted off on us in this way by industry.
Coke itself has many major industrial uses. Apart from the production of metals, it is used, for example, to reduce steam to hydrogen at high temperatures; and coke processed with lime produces calcium carbide. Calcium carbide is used to produce acetylene, which in turn is used to produce plastics and synthetic rubbers.
Products from the Distillation of Crude Petroleum
When crude petroleum is distilled in a similar way to coal tar, about half the number of compounds are produced, which are eventually used as fuels, solvents, paraffins, lubricants, and asphalt. The environmental effects of petroleum extraction are well known, as major oil spills are considered newsworthy events. Perhaps again the most damaging effect on the environment is the way in which the petroleum industry has been run for maximum profit. Even relatively toxic by-products have to find a use regard less of the detriments to human beings and their environment.
The oil industry is not an environmentally friendly one. Millions of tons of oil pollute the sea every year in completely preventable accidents. Considerable air pollution occurs with the leaking of methane and the burning off of unwanted products that could be used. Oil well blowouts and excessively high rates of extraction have had damaging environmental effects. The end products of oil refining—most notably gasoline—are sold so cheaply that we do not think twice about driving trivial distances for sheer convenience.
Plastics and paints are of special relevance to building and home- building, so we will look at them in some detail.
By plastics we mean the synthetic plastics produced mainly from coal tar and petroleum. There are many types of plastics, which can be categorized as either thermosets or thermoplastics, the latter accounting for about 80%. These thermoplastics can be melted by heat many times, whereas thermosets, as the name implies, set only once. Most plastics are produced from petroleum and natural gas.
Thermoplastics used in the building industry include polyvinyl chloride (PVC), polyethylene, polypropylene (PP), acrylics, polystyrene, nylon, polycarbonate, polyvinyl butytal, and cellulose. Thermosets include urea- formaldehyde, polyesters, polyurethane, and silicones.
The ecological impact of plastics comes not only from the energy costs in producing them, but also from the fact that most plastics do not biodegrade like vegetable or animal matter, or corrode like metals. In addition, most plastics can't easily be recycled or repaired. As a result, plastics end up being thrown away faster than any previous material and end up as a new form of pollution in the countryside and the sea. Some of them, particularly the thermoplastics, outgas gradually, releasing plasticizing agents and intermediate compounds. The amount of out-gassing depends to some extent on how well the plastic has been manufactured. Out-gassing increases with temperature, so it is a good idea to keep plastics away from heat sources in your home. If plastics catch fire, most burn easily, emitting thick, black toxic smoke. Plastics therefore need to be chosen with care, using natural alternatives wherever possible.
Paints and Varnishes
Paints are a mixture of pigments to give color, binder to bind them together, and a solvent to make the paint flow. In some cases all three pose a threat to the environment. Solvents are the most immediate pollutants, as they are substances that are intended to be evaporated off. It has been estimated that (globally) over 500,000 tons of solvent are released into the atmosphere from paints each year. Inside your house these solvents can damage the health of whoever is decorating if there is insufficient ventilation. Among the solvents that are toxic are:
• White spirit
In addition to the evaporation of solvents, paints can often continue to outgas small quantities of toxic vapor for a considerable time (see TOXINS and AIR). Also, during the production of synthetic paints there is often a huge amount of chemical waste—a hidden source of pollution. With some paints, several quarts of pollutant are produced for each of quart of paint that is manufactured.
The present rate of paint use is unsustainable in many different ways, largely because of the many toxic chemicals that are involved. We need to look carefully at all the possible alternatives to the existing toxic mixtures that are sold as paint. There are, of course, important differences between the damaging effects of different paints, but generally we can't continue to use them as we now do. Until more benign synthetic materials are developed, we should return to some of the more traditional ways of making paints from natural materials, such as linseed oil and turpentine.
PRIORITIES FOR ACTION
+ Choose bricks from companies that are working on improving their environmental performance.
+ Use cement sparingly.
+ Use glass products that increase energy conservation.
+ Choose durable and reliable metal appliances and equipment to avoid the need for replacement.
+ Choose lead-free pipes for plumbing and take care in removing and disposing of old flaking paint—it may contain lead.
+ Avoid aluminum products if a less energy-intensive material will perform the same task acceptably.
+ Use paints that are made with natural or benign constituents where possible. Clean your paintwork and use careful touching-up instead of wholesale repainting.
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