Castinstone? Melanie Clamp suggests a concrete philosophy for modern movement conservation. "New or old in style? It will all soon be old, and neither better nor worse.for that'. David Watkin, Morality & Architecture, p98 Acceptabledecay The decay of concrete architecture is one we witness every da ywithout realising it, as so much of our built environment is constructed using some form of concrete, forexample pavements, roads and btidges. This decay has taken a relatively short time to become apparent, and it does not display the time-honoured patina of historic masorny. Time and progress are so often encouraged and displayed in hist01icbuildings. CalkeAbbey inDerbyshire is not simply about the displaying of built fabric, but also the social decline of the aristocracy with a kind of decayed glamour. In the case of modern architecture however, such decay isoften interpreted as an unfo1tunate failure of technology that detracts from the original concept of an undefiled building. Materialdecay simply does notfittheconceptof'pure' form that such architecture embodies. Ancientv modern-the problemwith traditionalrepair The piecemeal consolidation and replacement of badly decayed material often considered acceptable for traditional masorny buildings is not necessarily an appropriate method for the conservation of concrete architecture. Manyhist01icbuildings are constructed of multiple elements that are small in scale,which when they deteriorate can be repaired or replaced in a piecemeal fashion stone by stone, or brick by brick; but while the conservation of these earlier buildings is generally based on material fabric, there may be other values relevant to modern movement restoration which should be explored before deciding on the priorities for conservation. New ideas as well as techniques were being tested on many modern buildings and in some instances it may be appropriate to preserve the authenticity of the 'concept', pa1ticularly if it is well documented. It may be purityoff01m,constructionalapproach, structural innovation or social interest that is the key to the cultural significance of the building. AtDudley Zoo, for example, it appears that technical innovation was not as much an issue as speed of construction, so it is likely that getting details absolutely crisp and perfect was not necessarily the highest priority. Concrete by its nature is monolithic, 26 Decayto columnat theElephantHouse,DudleyZoo. generally composed of a reinforced steel skeleton encased with concrete cast between tempora1y shuttering and in many early examples this perfo1med as both structure and envelope. It is the interdependency of this composition that iscriticaland any failure within itcompromises the integrity of the whole building. In such deterioration, problems generally occur from the inside out, and not the outside in as with most traditional structures. It isanalogous to iron cramps within masonry walls, where current practice is to locate, cut out and replace with a nonferrous alternative. This technique is applied to concrete in the form of patch repair although the reinforcement is the structure, rather than an addition, and cannot be easilyreplaced. Patch repairs of this kind have been carried out to nearly allofLubetkin'sstructures at Dudley Zoo over their 50 year life although the application of 'piecemeal consolidation' has not generally been successful and the repairs themselves have failed and are now considered to be defects. AtDudley, therefore, the same method used for traditional historic structures has proven not to be even a medium-term option. The concealment of patch repairs behind an overcoat of paint or other finish provides an extra layer of protection from the elements but can result in a complete change in appearance, particularly where the concrete was originally 'fair-faced'. The 'as new' finish may be unintentional but it can be difficult to prevent, as numerous repaired buildings illustrate.The aim should be to portray a 'conserved' building and CONSERVING TWENTIETH CENTURY BUILDINGS not a new one, and although as much original fabric should be preserved as possible, this often proves difficult with modern integralconstruction techniques. The idea of reversibility is also difficult to comply with when repairing concrete and overcladding is probably the most reversible and patch repair the least. However, overcladding can also modify the appearance more than any other technique Levelof intervention Much as there are levels of conservation (preservation, restoration, reconstruction, adaptation, maintenance), repair techniques have been introduced for concrete that address the limitations of patch repair and have varying impacts on the structure. The chosen method will depend on the conservation approach to the building which will be typically influenced by the owner's objectives, cost, longevity and aftercare requirements together with the cause and extent of deterioration (visible and potential). Diagnosis also differs from that for traditionalmasoruy structures due largely to the pattern of decay and the nature of the material. The repair method will largely depend on the cause of the decay, whether this is physical (freezethaw cracking), mechanical or chemical (carbonation or chloride attack), or a combination. Careful inspection and testing is important for correct diagnosis. This is often determined scientifically by a specialist as the condition survey of the structure must identify concealed and potential decay. As well as basic 'opening up' to determine the depth of reinforcement cover, a cover meter survey will determine the position of concealed reinforcement. Testing is also required to identify various material properties including the presence of chlorides and carbonation. Inspections range from hammer surveys, to determine loose or hollow material, to removing quantities of material. Thorough testing can be invasive and expensive but is generally a good investment to enable more accurate costings and prevent spiralling costs once work is on site. Alternativesolutions It is vital for the architect to understand Context65 March2000
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