Specifying appropriate conservation work

Policies of minimum intervention should be adopted wherever possible, but this approach should not be confused or advocated solely on the basis of idealistic principles, but must be tempered with sound practical experience. A balance must be struck and this needs to be guided by a developed understanding of how the ruin originally functioned within the natural environment as an intact building, and how this function has changed as the building has become a ruin. It is worth noting that in many cases the condition and rate of decay of a ruin stabilised when the remaining structure became naturally buried. Archaeological excavation and re-exposure of the ruin in an exposed climate will typically increase the levels of decay once again.

Historically, buildings were constructed as flexible structures using earth, lime or gypsum mortars in a composite construction which accommodated gradual movement. It is important that this flexibility be maintained or reinstated in any repair work. This can often be achieved by filling and deep tamping open joints with new earth, lime or gypsum mortars or by grouting voids within the wall with low-strength grouts based on hydraulic lime and bentonite. There is now a proven track record in using this approach — after all, buildings were historically repaired using materials that were locally sourced and closely matched the original materials.

Rigid repair solutions which advocate the use of stainless steel pins set in resin grouts, or reinforced concrete beams and buttresses are often problematic in the medium and long term since they create localised stiffness within the structure, resulting in pressure points which can cause cracking and displacement. These methods have often, in the past, been put forward as a 'minimal intervention' approach, and at first glance they may be more localised than grouting or repoint-ing, but once installed they are very difficult to remove or reverse. If some form of localised strengthening is

Figure 3.8 Alveolar weathering of White Mansfield sandstone. The age, weathering, and lack of maintenance and repair over the lifetime of a ruin are often associated with advanced patterns of decay.

required this can be achieved using more sympathetic methods. Rigid stainless pins set in resin can be substituted by flexible wire stitches set in a hydraulic lime grout. Reinforced ordinary Portland cement concrete wall heads can be replaced, in certain circumstances, by reinforced hydraulic lime concrete. Hard mortar caps can be replaced with soft, organic wall caps.

Whenever considering recommendations as part of a condition survey it is important to base the advice on a thorough understanding of the functional design of the original building and the influence of decay upon the fabric. Recommendations must always be made with the long-term well-being of the site in mind.

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