Directory of Traditional Building Skills - Mourne Heritage Trust

Research into the most appropriate ways of using lime as a material for repairing historicbuildings and monuments is ongoing. Please contact the UAHS for additional information onthis subject.STONEWORK REPAIRSThis is a complex subject which requires expert guidance. The choice of techniques availableis outlined below in a simplified form.The first step in any repair scheme is to evaluate the existing state of the stonework and thedegree of intervention and repair necessary. This evaluation has implications for the types ofrepair techniques to be undertaken and their application as exhibited by different stones orelements of the building. When various methods of repair are matched to particular stoneproblems, sometimes in one building or even a single façade, this is referred to as a ‘palette oftechniques’. The overriding principle is to retain as much as possible of the original stone.Repair Techniquesa) Complete stone replacementThis is an extreme measure, rarely necessary and very expensive, involving the completerebuilding of a façade or building. It is often difficult to obtain original or compatible stone andthis solution should only be used when there is complete failure of the stone or metal fixings.b) Replacement of individual stonesWeathering of stone is endlessly variable and individual stones may fail for many reasons –surface spalling, fixing failure, structural movement etc. Geological matching is critical toensure compatibility of future weathering. Stones can be replaced either to full depth or, morecommonly, to 75–100mm thickness, depending on the amount of decay of the original stone.Fixings may be necessary and should be of stainless steel to avoid corrosion.c) IndentingWhere only a small section of an original stone is damaged – e.g. by rusting around a railingfixing – it is more appropriate to replace only a small section of stone. The new stone needs tobe geologically matched, as noted above, to a similar 75–100mm depth, and should be tightlybutted to the original, without expressing the joint, and fixed as necessary. In finer work muchsmaller indents are possible, often held in place with epoxy grouts.d) Render repairsLarge scale render or ‘plastic’ repairs are now largely discredited though this is a usefultechnique for small scale repairs to complicated carvings or sculpture. The renders must be ofa ‘soft’ lime based mix to avoid accelerated weathering of surrounding stone. Stainless steelwire cages can be used to build up profiles. This is a technique for expert conservators, not acheap alternative to correct stone repairs.70