December 14, 2010
Iconic Canadian National Exhibition entrance gets painstaking makeover
In the 1920s, the term artificial stone was coined for precast concrete — a relatively new building material that was specified for the construction of the Princes’ Gates, the imposing Beaux-Arts style monument that stands at the eastern edge of the Canadian National Exhibition grounds in Toronto.
“Precast concrete was cutting edge technology in the 1920s,” an era when granite, limestone or sandstone were the choice materials for such monuments, says Arran Brannigan of the Limen Group Ltd., the masonry restoration contractor heading the ambitious project to restore and replicate the 83-year-old Gates over the next several months.
The contractor’s job calls for the replacement of the Gates’ weathered and worn 16 statues as well as the four main columns, capitals and the abacus supporting the central arch that towers about 80 feet above the entry to the exhibition grounds. Moulds of each piece will be cast and new precast elements will be made by Toronto-based Tri-Krete Ltd.
Disassembling the elements is a daunting task because the monument’s façade is keyed into the existing masonry backup wall, says Brannigan, Limen’s operations manager. “Nothing comes apart easily.”
Furthermore, there are no drawings on record of the original design, so Limen’s crew is in for a few surprises during the takedown. One recent discovery, for instance, was that stones in upper portions of the Gates and the precast pylons are 80 inches deep, weighing up to 10,000 pounds.
“We couldn’t have anticipated this,” he says, noting 45-ton cranes are required to remove the heavy elements. In the 1920s, chainfalls and pulley systems were the erection equipment for the job.
To support the arch during disassembly of the four supporting columns, a shoring framework made of steel I-beams and C-channels will be installed. Some of the shoring is tied into scaffolding, while other portions connect to the monument for support.
Limen’s crew will use wood and steel straps to frame each statue (the tallest stand 12 feet and weigh 1,800 pounds), and then all elements will be bound together by wire straps for support and weight displacement before being lifted by crane.
The stones around the base will first be removed to ensure the statues are not damaged when they are cut away from the bases, adds Brannigan.
Toronto-based Traditional Cut Stone Ltd. will restore and rebuild weathered features and missing anatomical details (a finger and nose are examples) to ensure accurate replication.
Prior to starting the project in September, Limen conducted a detailed survey of the monument and site. Digital photographs were scanned onto 3D software to map every detail, angle and elevation. The 3D images will be kept in the city’s archives for future reference, says Brannigan.
The new columns will meet modern code standards, which require rebar to help guard against earthquakes and cracking. New stone components are being resecured with stainless steel rod anchors, specialty masonry ties, to the backup masonry brick supplied by Ottawa-based Cintec Canada Limited.
Limen’s contract also calls for repointing “thousands of feet” of mortar joints at the wall stones. Using angle grinders, one-inch deep relief cuts will be made in the middle of each joint prior to removal of old mortar with hammers and chisels. The new mortar will be composed of Type N masonry cement.
Limen’s contract, worth just under $2 million, is slated for completion in late spring. “It’s a tight deadline for a project of this size,” says Brannigan, noting that the contract with the CNE stipulates that the road through the Gates can only be closed for a few days at a time. “It makes it tricky to schedule the trades.”
Along with Limen’s 12 masons, the site will see a crew from Unistruct Canada Limited for installation of a new catwalk, roof anchors and associated metal work. The electrical contract for lighting the monument was not awarded at press time.
The prime architectural consultant is Toronto-based James Bailey Architect. The structural sub consultant is Quebec-based Jokinen Engineering Services.
The Gates were built 1925-1927 for the 60th anniversary of Confederation. They are protected by the Ontario Heritage Act.
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