failure, as well as more detailed close-up information. Further investigation by other nondestructive techniques may be required, but these can be restricted to where they are needed. There is inevitably a downside, which is the equipment's extreme sensitivity to environmental conditions. Rain,wind and sunlight can all affect the level and reliability of information obtained. Sunlight on the elevation under inspection results in excessive reflected heat from the surfaces, making external survey impossible, but on the other hand, often creates sufficient thermal gradient to allow the necessary information to be obtained by an internal survey of the wall. In unheated buildings such as churches, solar gain creates sufficient thermal gradient to reveal construction details buried within thick stone walls. In heated buildings, the greatest amount of information is obtained on cold nights when the temperature differences across a structure and between different materials are most marked. Rain cools the surface and reduces emissivity: wind also tends to reduce temperature differences. • This sensitivity may seem to render the technique somewhat useless for external assessment in this country, but in fact the problems can usually be overcome by careful planning. The full potential of infra-red thermography has yet to be determined, and research is continuing, but there are many other applications for the technique, such as the location of failures in stone cladding and curtain walling. It is quite clear that a huge amount of data can be obtained: the skill lies in turning raw data into valuable information. In many cases, the sheer volume of data obtained can actually obscure that which isrelevant to the particular information required. For example, thermography will pick out changes in the size of aggregate used inarenderbecauseofthedifferingthermal masses involved, and also differentiate between lime and cement renders by virtue of their different moisture contents. This may be of interest and value, but can obscure or confuse the assessment of bond failure for which the particular NEWTECHNOLOGY FORCONSERVATION @ @ survey was commissioned. Some applications, such asthe location oftimber framing, is fairly easy to interpret, others like the assessment of bond failure in brickwork, require a high level of experience to interpret reliably. Ifloss of historic fabric, disruption and costs are to be minimised, it is vitally important that as much information as practicable is available on the construction, historical development and condition of a building before repairs or alterations are carried out. Would you like to be operated upon by a surgeon who had but a vague knowledge of your physiology, medical history and current ailments? .. Robert Demaus is a partner in the Demaus Partnership and may be contacted on 01568 615662. "IHAVEJUSTONEWORDTO SAY TO YOU ... PIASTICS" Mr McQuire in The Graduate (1967) Anthony Walker discusses and area of modern construction where preservation may not always be possible A very simple word for an incredibly varied range of materials, loved by some and hated by others but attracting a rapidly growing interest from collectors and conservators. Until recently polymers have only been of interest to Conservation Officers and building conservationists to tl1e extent that as silanes, epoxies and other sinillar products they are used to stabilise or repair more traditional materials. That situation is now changing rapidly for not only is the importance of plastics artefacts now widely recognised but also post-war buildings now being consideredfor listing incorporate a substantial proportion of plastics from cladding to paints, decorative laminates to door furniture, dpcs to plumbing. Plastics have been used in buildings throughout the century and from the 1950s onwards have invaded every aspect of construction. Any approach to the conservation of buildings of the 20th century will require an understanding of the materials, their CONTEXT49 historic significance, their durability and the processes of degradation. This article provides an introduction and some sources of further information. During the 19th century natural polymers were used more widely in buildings than is generally recognised. Gutta Percha, shellac and Bois Durci provided speaking tubes, coatings and A design for a Milk Bar by Maxwell Fry from the 1938 Rexine catalogue. 'Jbe Sylvia Katz collection. mouldings and had many other uses beside. At tl1e beginning of the 20th century the first fully synthetic materials were produced with discoveries by Baekeland in America and Swinburne in England leading to phenol formaldehyde moulding powders and resins. They became known under various trade names: Bakelite, Formica, Wareite among others for lan1inate sheets and Damard from Swinburne's Damard Lacquer Company for coating brass and other materials. Cellulose nitrate, discovered by the middle of the 19th century and known as Parkensite, Xylonite and most commonly Celluloid, was also used as a coating and formed the base for many paints during the 1920s and 1930s. One particularly unusual use was to provide a light-sensitive wall coating onto which a photographic image could be projected and fixed which was promoted as a time saving means of achieving a decorative finish. There is at least one recorded use of this technique at Wells Coates' Embassy 11
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