Endangered heritage

Masonry is widely recognised as a repository of much of the world's tangible cultural heritage. The stone has a finite life, that can be drastically curtailed when it is placed in the aggressive environments experienced in urban settings. Because of this it is essential that the choice of new and replacement stone and the conservation of decaying stone is underpinned by a detailed knowledge of how different stone types decay in specific environments and what factors trigger decay and control its rate once it is initiated.

Limestone is the main construction material used in many of the UK's most historic buildings. Unfortunately, much current knowledge on building stone decay appears to have been overly influenced by the performance characteristics of a limited number of comparatively durable stones. The difficulty for the majority of stone structures is, however, that they are not constructed of such limestones. There are many common building stones that do not decay gradually, but instead experience seemingly unpredictable, episodic and sometimes catastrophic breakdown. Episodes of rapid decay can be interspersed with periods of relative stability that may be marked by surface induration through, for example, the formation of a pollution-derived calcium sulphate crust. Important examples of these stones are the quartz sandstones widely used across north and northwest Europe. Characteristically, such stones are prone to disruption by accumulated salts that produce rapid surface retreat by contour scaling, granular disintegration, and flaking.

SWAPNET Meeting, Malta

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