Underlying issues on the selection, use and conservation of building limestone

Abstract

Abstract An argument is presented that, despite popular assumptions, many limestones, especially the wide range of clastic and, in general, granular limestones, do not decay in a steady and predictable pattern in response to slow dissolution. Instead these stones, especially when used in construction in polluted environments, invariably decay episodically through physical breakdown. Most commonly this is accomplished through a variety of salt weathering mechanisms that, if unconstrained, can lead to the rapid, catastrophic decay of building blocks and their complete loss – a process that has driven the extensive programmes of stone replacement that are typical of buildings constructed of these stones. In polluted environments, especially those rich in sulphur and particulates, the most common constraint on accelerated decay has been the rapid development of gypsum crusts that, for example, could rapidly ‘heal’ the scars left by contour scaling. It is ironic, therefore, that any reduction in pollution could conceivably lead to increased erosion by retarding this healing process. Because of this temporal variability of decay and its translation into spatial complexity, it is important that further research is undertaken to understand controls on the decay of these important building stones so that future conservation strategies can be appropriately informed.