Visual assessment of sandstone building façades: condition factors related to cleaning

Cleaning of traditional stone building facades became widespread from the 1960s in many cities across the UK, where it became a totemic factor in economic and social regeneration. Debate continues on the effects of cleaning on the health of stone buildings, often without a sound evidence base for decision making. In this study we attempt to determine whether stone cleaning is a stone decay factor. A survey technique based on assessing selected blocks in buildings, excluding areas where multiple factors contribute to high risk of decay, was applied in a semi-quantitative analysis of buildings in Paisley constructed from blonde-coloured carbonate-cemented quartz arenite, to recognize decay problems related to cleaning. Amounts of decay were evaluated on blocks from cleaned and non-cleaned buildings. The results show that there is no significant difference in amount of decay between these groups of buildings when areas subject to high decay stress are disregarded, and therefore that cleaning is not a risk factor in the stone surveyed. Decay is strongly centred on building elements that have a high risk of decay, with a strong predeposition towards moisture retention and associated soiling (i.e. projecting and recessed ornament and architectural detail).