Context 164 - May 2020

22 C O N T E X T 1 6 4 : M A Y 2 0 2 0 KINLAY LAIDLAW Conserving Burns Monument Water penetration to Burns Monument in Alloway, Ayrshire, constructed in the 1820s to a design by Thomas Hamilton Junior, has been prevented using lime grout and injection mortars. Water penetration of traditional solid mass masonry is becoming an increasingly common issue. While traditional solid mass masonry has performed very well in past centuries, with the extremes of weather in such exposed locations as the west of Scotland, we are aware of increasing instances of water penetration in traditional masonry buildings, including those that have been subject to conservation repair, especially where repointing is involved. Ayrshire in south-west Scotland experiences around 200 rainy days a year, contributing to around 1,500mm annual rainfall and an average relative humidity of 90 per cent. These are challenging conditions for any building to weather and provide a comfortable dry internal environment. Burns Monument was constructed 1820–23 to a clever design by architectThomas Hamilton Junior, based on the ancient Greek choragic monument of Lysicrates, and incorporating much symbolism commemorating poet Robert Burns’ achievements and his associations with freemasonry. It is constructed of traditional composite masonry of two skins of ashlar sand- stone with a central core of lime mortar and rubble. The ashlar is of the finest quality, using durable Scottish sandstones cut and wrought in the finest stonemasonry practices of the time. It has always been a popular visitor attraction, and is now Category A listed by Historic Environment Scotland (HES) and visited by over 100,000 a year. Water penetration and surveys The property came into the care of the National Trust for Scotland (NTS) in 2008. Serious dampness to the interior masonry was evident from this point. Initial condition surveys revealed that a high proportion of mortar joints were either open or had been repointed with various mortars over a number of successive attempts, but underneath the surface skin the joints were open. Further investigation revealed that many of these voids led straight into the core masonry, providing a clear route for water to enter and saturate the structure. Between 2008 and 2016, during a period of further surveys and monitoring, the effects of water penetration on the ashlar interior worsened significantly. It was clear that the issue was progressive, and was beginning to cause irreversible damage and disfigurement to the carved and embellished ashlar masonry interior. Concurrent investigations of the archive record revealed that the original architect’s specification for the fine ashlar jointing mortar required white lead, linseed oil and chalk filler. This had evidently washed out over the years leaving voided mortar joints.We also realised that many beds of large masonry units had been left empty during construction. Pads of mortar placed only at either end allowed the masons to tap each ashlar stone into place, fitting accurately against adjacent stones; something they could not have achieved if the beds had been completely filled with mortar. Burns Monument before the 2018 grouting works