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:
- waterproofing foundation walls and installing a below-grade drainage system;
- installing stainless steel helical masonry ties;
- injecting a cellular foamed cement grout within the inner core rubble (Figure 5);
- repairing cracked masonry units and building trim; and
- completely repointing the front and side elevations. (A detailed description of this type of restoration work can be found in a previous article by this author, “Stabilizing Cracked Masonry: A case study” in the January 2007 issue of Construction Canada).
Below-grade waterproofing of the rear elevation foundations was carried out a few years later.
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).