Cracked and deteriorated masonry joints were cut out and repointed using the repointing mortar, and damaged masonry and building trim units were repaired using the prepackaged heritage repair mortar (Figure 13). The repointing mortar’s colour was selected to blend with the existing mortar. Although the repair mortar’s colour was selected so repairs would blend well with the surrounding natural stone, the intent was they should not be disguised.

During the pre-conservation investigations, it had been observed heavy soiling was causing damage to the natural stone masonry units in some areas (Figure 14). The damage, in the form of scaling and flaking, was the result of the soiling reducing the stone’s natural ability to transmit moisture vapour to the exterior. When a rapid fall in temperature follows a mild, wet day, the inability to dry causes the stone to suffer the effects of freezing as the vapour undergoes condensation.

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Therefore, part of the conservation strategy included cleaning to remove the heavy soiling and thereby improve the masonry’s ability to rapidly dry. Trials were specified to be carried out in advance of cleaning to ensure the selected cleaning method could achieve the objective without causing damage to the underlying substrate (Figure 15). The successful trials resulted in approval being given for the contractor to use a low-pressure cleaning system using glass beads and water.

As mentioned, the sill units where the columns were seated were damaged beyond repair and the conservation strategy therefore required their replacement. Unfortunately, natural stone that would blend reasonably well with the original sandstone was not available within the project period. In fact, although the replacement stone texture, fabrication, and tooled finish were acceptable, the colour of the stone supplied and installed was considered to be inappropriate and adversely impacting on the building’s esthetic quality. For unacceptable delays to the project and additional high cost to be avoided while an alternative stone was sourced, a compromise was decided on and the new units were stained in-situ to blend with the originals (Figure 16).

As part of the strategy to improve the way in which gravity loads are transferred from the friezes through the columns, the sill unit lengths were modified so they were centralized under the columns (Figure 17).

Conclusion
The development and implementation of the described strategies for restoring structural stability and durability to the Owens Art Gallery followed a holistic approach. The fact that those who have been familiar with the building for many years consider the appearance of the art gallery to remain unchanged (apart from the cleaned masonry) attests to the success of the strategy that also required the objectives be achieved while respecting the historical fabric of the local landmark (Figure 18).

Paul Jeffs has more than 40 years of experience in the construction industry around the world. He is principal of PJ Materials Consultants Ltd., a Guelph, Ont.-based company that provides consulting services across Canada for the construction and restoration of masonry and concrete structures. Jeffs can be contacted via e-mail at pjeffs@pjmc.net.