10 Photograph and thermograph of timber stud and render 'battlements' manifest themselves a great distance from their source, and it can be extremely difficult to locate the course of moisture movement through a building. Standard commercially available moisture meters are notoriously unreliable, and in any case usually cannot provide a sufficiently broad picture to establish large-scale patterns of such movement. Unless these sources are located and remedied, other problems that may exist within the building, such as timber decay, cannot be satisfactorily dealt with. Equally, changes to the internal environment of the building, such as the installation of underfloor heating, can have unpredictable effects on moisture patterns which thermal imaging can monitor. Where remedial treatments such as injected damp-proof courses have been used, faults and breaks in the barrier can be detected. CONDITION OF AND HISTORIC REPAIRSTO ORNATECEILINGS Very often it is not the plasterwork itself that is of concern, but the condition of the supporting structure that requires investigation. Ornate ceilings can be evaluated on the same basis as the assessment of frames behind render discussed above, again using a micro-drill to assess the condition of the supporting structure once located. Temporary heat sources are sometimes required to achieve the necessary temperature differences. There is some indication that thermal imaging may be able to differentiate between lime-and gypsum-based plasters, and identify previous repairs and alterations, perhaps due to differences in emissivity and density, but further research is required. STRUCTURALFAILURESIN BRICKWORK Loss of bond between facing and stock brick behind, which was never more than mildly affectionate in many a Georgian speculative development, can be identified by thermal imaging before failure becomes all too obvious. Other possible problem areas such as decayed bonding timbers can also be located. Not all bulges in walls are structurally serious, but how many buildings have been unnecessarily underpinned and/or rebuilt by over-cautious or under-informed (or both and worse) engineers and surveyors who have failed to identify the real problems? ARCHAEOLOGICALRECORDING FOR LISTING PURPOSES, CONSERVATION AREASETC The wealth of information provided by thermographic images, and the speed and ease with which that information can be obtained, makes this technique an invaluable tool for resurveys etc. A street elevation of thirty houses can be recorded in less than 30 minutes, simply by walking along the opposite side of the street, with no access equipment and no disturbance to occupiers or others. This provides a record of the original method of CDnStructionand any subsequent changes to the building. So many buildings have been updated and altered over the centuries that this kind of information allows a far greater understanding of the development of a street or village. MONITORING OF FRAGILEMURALS AND REMEDIALTREATMENTS Thermography has proved itself useful in preliminary diagnostic investigations for the conservation of murals. Very often the fragility of murals, particularly in • churches, is caused not so much by the materials of the mural itself, but by the prevailing environment and problems with the substrate. Many of these problems such as salt crystallisation and mould growth are caused by moisture and thermal variations through the fabric of the building. Thermography can identify and monitor these patterns enabling a far greater understanding to be obtained of the mechanisms creating the problems. The above gives a general view of some of the many applications in which infra-red thermography gives valuable information. The power of the technique lies in its speed and ease of use from ground level, and its ability to provide a broad picture of patterns of structure and CONTEXT49
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