CONTEXT 189 : SEPTEMBER 2026 21 INFRASTRUCTURE CLARA WILLETT The right stone The Building Stone Database for England provides a framework for identifying historic building stones and informing decisions about their use in heritage practice. England’s rich architectural heritage is strongly shaped by the wide variety of stones used in its buildings and structures. These building stones typically reflect the underlying local geology, and contribute significantly to the distinctive character of towns, villages and the wider rural landscape. Repairing and adapting these buildings and structures sustainably depends on understanding the stones from which they are made. Only with this knowledge can compatible materials be selected. Unless the stone has demonstrably underperformed – which is rare, as decay is typically due to interventions such as impervious or overly hard mortars that redirect moisture through the stone rather than the joints, lack of protective lime finishes (where appropriate), and rainwater management issues – any replacement should replicate the properties of the original. These include mineral composition and physical characteristics, particularly porosity and permeability. Incompatible replacement stones can cause serious problems. For example, a high-magnesian limestone introduced into high-calcium limestone masonry may give rise to deleterious salt formation. A replacement stone that is less porous than the original, including some cement-based cast stones, may alter moisture movement through the wall and accelerate the decay of adjacent historic fabric. Visual similarity alone is therefore not enough. Stones that are not materially compatible are also likely to weather differently over time, undermining both performance and appearance. These issues are not confined to repair. In conservation areas and other historically sensitive contexts, new buildings and extensions should be designed in a way that is sympathetic to local character and history and, where relevant, contributes positively to local distinctiveness. This may include the use of materials that respond appropriately to local building traditions. Where stone is proposed, access to a suitable source may therefore be an important practical consideration. However, even when an appropriate stone has been identified, it can be extremely difficult to Cottages built from local Tresco Granite, Cornwall (Photo: Geckoella Ltd for Historic England) THREATENED MATERIALS AND CRAFTS
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