Ontario Construction News staff writer
A sold-out crowd of nearly 70 construction and heritage professionals gathered at Saint Brigid’s Centre for the Arts on Nov. 6 to hear internationally recognized conservation engineer Dr. David Wiggins challenge conventional wisdom on historic masonry.
Hosted by the Construction Specifications Canada (CSC) Ottawa Chapter, the full-day seminar, titled “An Engineer’s View of Lime-Mortared Masonry,” drew attendees from across the structural, architectural, and restoration sectors. CSC National President Abigail MacEachern was also in attendance to support the local chapter.
Wiggins, a CARE Accredited Engineer and director at UK-based Clach Conservation Engineering Ltd., holds a doctorate in the technical conservation of heritage masonry. His portfolio includes structural assessments of prominent UK landmarks such as Durham Castle and Carlisle Castle
In the morning session, Wiggins focused on the structural aspects of lime-mortared masonry, covering strength, stability, and stiffness. He explained how masonry units and mortar work together, and why mortar strength alone does not determine the strength of the overall masonry.
He also highlighted lime mortar’s ability to accommodate movement and the influence of mortar joint thickness on masonry stiffness. Using the rebuilding of buttresses at York Minster as an example, he showed how air lime mortar can become load bearing before full carbonation. The example highlighted the distinction between early load-bearing capacity and carbonation’s contribution to long-term durability.
In the afternoon session on fabric pathology, Wiggins covered porous materials science, decay, and compatible repair in the context of historic masonry conservation. He explored how moisture moves through masonry and how lime mortar supports capillary drying, helping manage the risks of frost damage and salt-related decay.
He emphasized the importance of selecting repairs that are compatible with the existing masonry’s structural properties and moisture behaviour. He illustrated these principles through case studies at Carlisle Castle and Clitheroe Castle, showing how repair strategies were tailored to each site’s conditions. The examples highlighted moisture management, mortar selection, and techniques such as rebuilding, repointing, and grouting.
Wiggins delivered a strong warning against the use of chemical admixtures or “snake oil” in modern proprietary repair mortars. He noted that adding air entrainers, water retainers, or water repellents alters the mortar’s microstructure, ruins the wick action necessary for capillary drying, and ultimately accelerates masonry decay by displacing the drying front into the masonry units.
Following an interactive question-and-answer period, the CSC Ottawa Chapter reported that the presentation generated highly positive feedback from the local construction community.
The event was made possible through the backing of numerous industry sponsors, including the Canada Masonry Design Centre, Ontario Masonry Contractors’ Association (OMCA), Sika, John G. Cooke & Associates Ltd., Pomerleau, Tacoma Engineers Inc., Heritage Restoration Inc., Atwill-Morin, Robertson Restoration, Ottawa Region Masonry Contractors Association (ORMCA), ERA Architects Inc., Heather & Little Limited, Permacon, and Hobson Built Heritage.
