Magnesian limestone is a key construction component of many historic buildings that is under constant attack from environmental pollutants notably by oxides of sulfur via acid rain, particulate matter sulfate and gaseous SO 2 emissions. Hydrophobic surface coatings offer a potential route to protect existing stonework in cultural heritage sites, however, many available coatings act by blocking the stone microstructure, preventing it from 'breathing' and promoting mould growth and salt efflorescence. Here we report on a conformal surface modification method using self-assembled monolayers of naturally sourced free fatty acids combined with sub-monolayer fluorinated alkyl silanes to generate hydrophobic (HP) and super hydrophobic (SHP) coatings on calcite. We demonstrate the efficacy of these HP and SHP surface coatings for increasing limestone resistance to sulfation, and thus retarding gypsum formation under SO/H O and model acid rain environments. SHP treatment of 19th century stone from York Minster suppresses sulfuric acid permeation.
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We acknowledge the following organisations for funding: The Science Heritage Scheme, AHRC/EPSRC and York Minster for the award of a studentship to RW and the Welsh Livery Trust for a travel bursary. The Royal Society and the EPSRC are respectively acknowledged for the award of an Industry Fellowship to KW and a Leadership Fellowship to AFL (EP/G007594/2). In-situ XPS studies are based upon work part supported by the US-National Science Foundation (NSF) under CHE095260 to VHG. We also thank Mr Andrew Arroll, Drs Kate Giles and Alex Holton for useful discussions concerning limestone weathering.