established use in buildings as a quick and very cost-effective method of detecting excess heat loss, which can in itself be just as important in a historic building as any other. Recent and continuing research has demonstrated that it is also extremely useful in a wide range of other applications including the location and/or assessment of the following. CONCEALEDSTRUCTIJRALTIMBER FRAMES The building illustrated is typical of thousands in towns and villages throughout the country. It has been rendered externally and lined out internally, so there is no easy way of determining how it was built, orwhat alterations have taken place. The window positions in the gable elevation suggest it was originally timber framed, but not necessarily whether it is still framed or, if so, exactly where the structural members are. The thermographic image shows very clearly the structure behind the render. Various points that become immediately apparent are: ■ the gable elevation is timber-framed, ■ the windows do not relate to structural members, ■ the framing pattern changes halfway up the wall, ■ the frame is independent of the chimney in the comer, ■ the front elevation has been rebuilt in brick, ■ there do not appear to be any major structural defects such as cut or missing principal members. All this information can be obtained inI t I [ CONTEXT49 stantly from street level, allowing far more informed decisions to be made about any proposed changes or works to the building. Simply as an archaeological tool it is of enormous value, but once the structure has been so accurately defined, it is also possible to test the condition and integrity of every member of the frame using micro-drilling techniques (see Context 39, p25) through 2mm pilot holes drilled through the render. Any repairs found to be necessary can be carried out without removing any more render or internal finishes than absolutely necessary. To assess the structure and condition of this building in any otherwaywould involve stripping allthe render offthe outside, or removing much of the internal finishes and decorations, and then replacing them, with all the concomitant loss of original or historic fabric, disruption and expense. How many times have important, or at least perfectly satisfactory, external and internal finishes been destroyed unnecessarily? CONCEALEDSTRUCTURALJOINTS, OPENINGSETCIN MASONRYWALLS Thermographic imaging reveals the differing thermal properties of materials within a wall, thus identifying where there have been changes to the structure. This can be very valuable in an archaeological/historical survey of a building, but can also provide vital structural information. As an example, at a church in midWales which has suffered massive stability problems, and which it was intended to underpin, thermography revealed a straight joint with dressed quoins in the 23 22 21 20 19 18 17 16 15 14 13 12 11.3 NEWTECHNOLOGY FORCONSERVATION (8) (8) stonework of one side wall, for which there was no visible evidence. This has significant implications for the pattern of underpinning. Similarly,old window and door openings are clearly shown by thermographic imaging. These reveal a great deal of the history of a building, and have considerable structural implications if new openings are proposed. BOND FAILURESAND MOISTURE INGRESSIN PARGETTING,HARLING AND RENDERS If a render becomes partially detached from the mass of wall behind, it shows clearly on a thermographic image because it warms up and cools down more rapidly than the fully bonded areas of render. This allows a very quick assessment of the condition of renders without the expense of scaffolding or specialist access equipment. Very often, it can be demonstrated that only localised repairs are necessary, which can be particularly important in areas where decorative pargetting is prevalent. LOCATIONAND TRACKINGOF LEAKS,RISINGDAMPETC Damp, and its causes and effects, are frequently misdiagnosed in buildings. A leading independent expert in the field has stated that around 70% of remedial damp treatments are unnecessary and, of those that are, around half are unsuccessful. The effects of excess moisture can Photograph and thermograph of typical building (described in the text) 9
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