Environment: Chemical treatment helps ancient buildings weather the storms

Scientists have developed a technique that could help to protect historic stone structures, such as York Minster in the UK, from the effects of weathering by atmospheric pollutants. The findings (funded through the EPSRC/AHRC Science & Heritage Programme), reported in the journal Scientific Reports this week, could be used to promote the conservation of other historic buildings made from limestone.

York Minster is the largest Gothic cathedral in northern Europe and has occupied the same site since 600 AD. Along with many other historic structures of its era, York Minster is eroding at a noticeable rate and periodic renovations and attempted restoration efforts using the best materials available at the time have, in some cases, accelerated the decay.

Hydrophobic surface coatings offer a potential route to protect existing stonework in cultural heritage sites, but many available coatings act by blocking the stone microstructure, preventing it from ‘breathing.’ Karen Wilson and colleagues report a conformal surface modification method, using a self-assembled single layer of fatty acids combined with another fluorinated chemical compound, to generate hydrophobic and super-hydrophobic surface coatings on calcite. The treatment, when applied to 19th century stone from York Minster, suppresses sulphuric acid permeation, thereby delaying gypsum formation under controlled dry and humid sulphur dioxide environments.