Bioremediation of weathered-building stone surfaces.

Atmospheric pollution and weathering of stone surfaces in urban historic buildings frequently results in disfigurement or damage by salt crust formation (often gypsum), presenting opportunities for bioremediation using microorganisms. Conventional techniques for the removal of these salt crusts from stone have several disadvantages: they can cause colour changes; adversely affect the movement of salts within the stone structure; or remove excessive amounts of the original surface. Although microorganisms are commonly associated with detrimental effects to the integrity of stone structures, there is growing evidence that they can be used to treat this type of stone deterioration in objects of historical and cultural significance. In particular, the ability and potential of different microorganisms to either remove sulfate crusts or form sacrificial layers of calcite that consolidate mineral surfaces have been demonstrated. Current research suggests that bioremediation has the potential to offer an additional technology to conservators working to restore stone surfaces in heritage buildings.