Lime mortar and sacrificial protection of heritage stonework Available to Purchase

Microstructural characteristics of historic Scottish sandstone and lime mortar are reviewed against the physical principles underlying the function of a desalination poultice. The functional role of lime mortar as a permanent poultice enhancing the durability of heritage masonry is presented. The materials’ porosities and pore size distributions are characterised using mercury intrusion porosimetry and validated through scanning electron microscopy. Key findings include the respective predominant pore ranges exhibited by lime mortar (c. 500–2000 nm) and sandstone (c. 10 000–25 000 nm), which together interact to invoke stonework’s unique response to moisture. A technical understanding of this sacrificial protection to stonework afforded by lime mortar is imperative to avoid the use of inappropriate materials. Such incompatible materials upset the mechanisms underlying the functional role of the mortar, leading to damage of heritage stonework. The optimal example set down by historic limes appears to be best replicated by the specification of lime mortars with a high degree of carbonation set, to which much of the predominant 500–2000 nm pore range formation is attributable.