The choice of building materials, which was very limited until the eighteenth century, has greatly increased and will continue to do so.?Since any number of different materials are presently suitable for a particular building application, the designer must make a choice.?Although cost is often a determining factor, particularly if the material is not to be visible, aesthetic considerations become important when a material occupies a prominent place in a building, and durability is an important aspect of aesthetics.

Natural materials, such as wood, stone, and mudbrick, are the oldest building materials. Almost as old are simple manufactured materials, such as hard-burnt bricks and iron, made by subjecting the raw materials to a high temperature. Products made by more complex processes are mostly of recent origin, and new materials are constantly being added to the list.?

Fitness for the intended purpose remains the prime criterion, but cost, as remarked previously, is often a determining factor. Thus, the replacement of natural stone-the predominant material for important buildings in most countries until the eighteenth century by brick and concrete was purely the result of their lower cost. Stone is today used mainly as a veneer where a good surface finish is required.

In the late 1970s, when energy was in short supply in many countries, energy conservation in buildings was a major concern.?Logically, this should encompass not merely a reduction in the use of energy required for heating and cooling buildings, but also a?preference for materials and building processes that require as little energy as possible.

The cost of labor is another major consideration in the choice of materials. Raw materials that are relatively cheap in themselves may be expensive to form. For example, the cost of the stone used in buildings today is mainly the cost of labor. Flat surfaces can be cut by methods that are much more efficient than those employed before the eighteenth century, but complex shapes still have to be cut with a mallet and chisel in a manner that does not differ greatly from that used in Ancient Egypt. By contrast, concrete can be cast into a mold without any cutting at all.

The rapid increase in the use of plastics is largely due to the ease with which they may be formed into complex shapes at low cost by mass production methods.

In the long term, a number of materials presently in common use will probably become exhausted, notably some metals and some varieties of stone, but other materials will adequately replace them.?The raw materials for concrete, glass, bricks, and aluminum are available in very large quantities, although the cost may increase if less economic raw materials have to be used.

The number of readily available building materials and components has grown rapidly during the twentieth century and continues to grow. The best sources of information are the manufacturers themselves;?most will readily supply technical?information in great detail on request. This information is generally reliable in its positive aspects, since manufacturers and material suppliers who wish to remain in business will not knowingly give any information that is incorrect. Some suppliers will point out that their material cannot be used in certain ways; others prefer not to mention?adverse information, and the architect or engineer has to infer its existence from the fact that appropriate positive statements are missing from a catalogue.

A great deal of information can be gathered from other periodical literature. This can be divided into several categories.?The first?consists of advertisements and short news items provided by manufacturers and suppliers. These are ordinarily sent to interested architects and engineers free of charge and include a card so that readers may write for further information on any items mentioned.?These publications constitute, in fact, a regular update of the trade?Literature.?

A second type of literature, the trade journal, is sold at a relatively modest price to individual subscribers and contains independently written articles that may contain critical comment on new materials and methods. The fact that these publications derive a substantial part of their income from advertisements usually does not restrain critical remarks on the materials advertised, but it may do so in some periodicals.

The third type is the journal that contains scientific papers, often of a highly specialized character. These journals may be published by professional societies or by scientific publishers; they do not normally carry any advertisements by manufacturers and suppliers of materials; and they have an editorial board of eminent specialists in the field to ensure that the papers published are factually correct and meet a high scientific standard. Their price is generally so high that libraries are the principal subscribers.

Cost remains a principal criterion of choice, particularly if a material will not be visible in the completed building. There is, for example, little difference between the performance of structural-steel?frames and reinforced-concrete frames if they are properly designed.?The cheaper of the two is usually selected, making due allowance for the effect of earlier or later completion time on cost and profitability.

Prior to 1950, steel frames were used for most high-rise buildings because they usually cost less than reinforced-concrete frames. Since then, concrete has become more competitive, but this has not been a steady progress. Although the majority of tall buildings in Europe and Australia are now built with concrete frames, this is not the case in North America. The choice has thus varied with time and geographic location.

For visible materials, aesthetic considerations?are often?dominant, and as beauty is to a certain extent in the eye of the beholder, the choice varies from one designer to another, and from one client to another.

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