Owens Art Gallery: A holistic conservation strategy

by Elaina Adams | May 1, 2012 11:33 am

Photo © Paul Jeffs[1]
Photo © Paul Jeffs

By Paul Jeffs
Located on Mount Allison University’s campus in Sackville, N.B., the Owens Art Gallery is the oldest university art gallery in Canada. (The author would like to thank Mount Allison University for permission to use the campus building as a case study for this article). Officially opened in 1895, the gallery was designed in the elegant Beaux-Arts style by highly regarded Toronto-based architect, Edmund Burke (Figure 1). Locally quarried and fabricated olive sandstone was used to construct the traditional mass masonry exterior walls, and decorative terra cotta friezes bearing the names of famous artists were incorporated within the front and side elevations and supported on circular sandstone columns.

Originally, the building served the community with a regionally renowned art gallery and museum and also housed the university’s learning centre for fine arts. However, in the early 1970s, the fine arts department was transferred to an adjacent newly constructed facility and the old building was upgraded to provide its predominant use as an art gallery. The major renovation work included:

Post-renovation cracking
Some time after rehabilitation of the gallery, cracks within masonry walls and columns supporting the friezes became evident and began to propagate over time (Figure 3). By the mid-90s, it was determined the roof reconstruction work had most likely changed how loads were distributed and had resulted in an overload condition, predominantly within the exterior wythe of masonry. There was also some evidence of lateral movement of some masonry units, as well as some out-of-vertical plane displacement.

Since it was also determined rainwater entering cracks over time could have caused deterioration of the inner core rubble within the masonry walls, it was considered likely voids had been formed. These would likely have contributed to an overload condition within the exterior wythe, thereby exacerbating the cracking and creating a destabilized condition.

1990s investigation and restoration project
In 1995, this author used impact-echo non-destructive testing techniques (NDT), as well as inspections through drilled holes using a fibre optic boroscope, to confirm the presence of voids and deterioration within the hidden core of the masonry (Figure 4).

In 1996, a major restoration project was implemented, consisting of:

Below-grade waterproofing of the rear elevation foundations was carried out a few years later.

2009 investigations
Although the restoration work appeared to correct the problem of lateral movement and out-of-vertical plane displacement, cracking continued––it became evident the overload condition still existed within the outer wythe. By 2009, the sill units on which the columns were seated had become damaged to the point a successful repair would be unlikely. Many of the cracks that had previously been repaired had re-opened and more had occurred (Figure 6).

Further investigations were therefore carried out to re-evaluate the cause of the overload condition, and this included the creation of openings within both the exterior and interior wythes so the masonry assembly construction could be better understood. These evaluations confirmed the assembly construction varied considerably between areas. In some locations, above the foundation level the backup masonry was a single-wythe brick construction, while it was a double-wythe in others.

During the 1970s renovation work, access to the roof overhang’s interior portion had been sealed off by construction of a block wall within the attic. Therefore, the 2009 investigation included creating access from the exterior overhang soffit. This revealed the root cause of the overload problem––the design of the new roof structure had incorrectly positioned the steel stub column bases within the middle section of the masonry walls, directly over the inner core rubble (Figure 7).

The inappropriate location of the stub columns concentrated gravity loads directly within the inner core rubble until they were subsequently transferred to the outer wythe by masonry units that projected across the core from the exterior. In particular, the columns supporting the friezes on the front elevation then became overloaded and transferred stress to the sill units. The fact the vertical joints between the frieze surround units had been constructed to align over the column capitals––and the joints between sill units to align under the column bases––only exacerbated the condition (Figure 8).

2010 conservation strategy
By necessity, the strategy developed for the 2010 conservation project was multi-faceted. It was designed to:

The conservation philosophy mandated the objectives of the strategy should be achieved using materials and techniques sympathetic to the masonry’s sensitive heritage fabric. It was therefore a specified requirement that, to the greatest extent possible, the work should be of the highest quality using traditional materials and techniques, supplemented with proven modern technology that would restore long-lasting structural stability and durability to the building.

Scope of work
The work to correct the overload condition from the roof was carried out under a separate project, which also included re-roofing work and replacement of the overhang soffit panels. (The author was the prime consultant for the exterior masonry restoration project. The contractor was Empire Restoration (New Hamburg, Ont.), the prime consultant for the interior restoration and the re-roofing project was Arthur J Arsenault Architect Ltd. (Sackville, N.B.), the structural engineer was J.M. Giffin Engineering Inc. (Amherst, N.S.), and the contractor was Can-Tech Construction Ltd. (Sackville, N.B.). The author provided sub-consulting services for the masonry-related aspects of the interior restoration). From within the art gallery’s interior, openings were made within the backup masonry at the stub column locations. New structural steel columns were then installed so they were supported on double-wythe backup masonry (Figures 9 and 10) and the masonry rebuilt to encapsulate them. The roof trusses were then permanently connected to the columns and the old stub columns disconnected so loads from the roof superstructure were transferred to the back-up masonry.

With roof loads removed from the inner core rubble, adjustable props were installed to temporarily support the friezes on the front elevation, and the columns were then progressively strapped and removed (Figure 11). The column capitals were also removed. With access now provided to the underside of the frieze surround units, stainless steel helical ties were installed upward at angles to intersect either side of the joints; the objective was to provide more effective spanning of load from the friezes across the tops of the columns once they were relocated.

The cracked columns were subsequently repaired using stitching techniques––short lengths of stainless steel helical ties were installed into pilot holes drilled at angles alternately along the length of the cracks so the ties intersected the cracks. The ties were slightly recessed and the entrance holes repaired using a prepackaged heritage repair mortar designed for sandstone. The crack openings were then cut out and repaired using the same mortar. When they were finally reinstalled, the columns were rotated so cracked sections were predominantly hidden.

Crack openings in masonry units were also chased and repaired using the heritage mortar. Additionally, selected horizontal mortar joints above cracked masonry units were cut out and lengths of deformable stainless steel helical reinforcing rod were grouted into the slots using a high-strength grout. The front portion of the joints was then repointed using a prepackaged hydraulic lime-based repointing mortar designed for use on heritage structures (Figure 12). (This technique is described in this author’s article, “A Tale of Two Towers,” from the November 2008 issue of Construction Canada[3]). The objective of installing joint reinforcement was to improve load transfer away from previously cracked sections, without significantly affecting the masonry’s ability to accommodate the influences of natural movement during extreme temperature changes.

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.

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).

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.

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  3. Construction Canada: http://www.constructioncanada.net/wp-admin/post.php?post=13756&action=edit

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