Carving into Toronto St. Michael’s Cathedral sandstone replacement

Since Traditional Cut Stone Ltd. started work a couple of months ago to reproduce sandstone details at the restoration of the 145-year-old St. Michael’s Cathedral in downtown Toronto, its scope of work has expanded. Considerably.

That is because architectural details initially thought repairable were anything but. In fact, many elements such as floret (sandstone flower carvings) petals and leaves had simply washed away from years of harsh weather, says David Tyrrell, a principal of the carving shop, which was retained by Clifford Restoration Ltd. to create the stone replacements.

Considerable wear from the forces of nature can be expected for a masonry building almost 150 years old. The porous side of some of the sandstone faced the weather, speeding up some of the deterioration — especially during harsh freeze/thaw cycles over the years, says Tyrrell.

The stone carving shop’s job entails replacement of: all finials; balustrade at roof level; inside/outside main spires; window hood mouldings; florets in the cornice below the balustrade; upper pinnacle shaft and buttress stones; pilaster capitals; stoned copings; gable traceries and capitals and some of the plinth blocks at grade.

To find appropriate replacement stone for the original Berea sandstone, which came from now-dried up quarries in the Caledon area, Tyrrell crossed Lake Erie to a quarry in Cleveland — once one of the biggest quarries in the world. “It has exactly the same geological makeup as the original quarries.”

Tyrrell says he spent over a year searching the quarry for “the clearest sandstone” best suited to withstand the weather for many years.

Fifteen truckloads of sandstone block weighing about 300 tonnes were transported to the contractor’s 20,000-square-foot fabrication facility in Mississauga. “It was the equivalent of moving a mountain into our back yard.”

The first step to recreating the details was to take accurate dimensions and photographs of the building and then creating drawings (“basically true-to-size artistic renderings”) which were then transferred in 3D to CAD, he says.

The company was fortunate to be supplied with original 1860s drawings through the restoration project’s architect, The Ventin Group Ltd.

Clay models were then made and reviewed by the owner and architect before plaster casts were made to be used as “models” for the carvers to work from, says Tyrrell.

The sandstone blocks, typically 5-8 tonnes each – were sawed into pieces usually about 300-500 pounds. Many pieces eyed for such elements as finials and corbel brackets required bed heights of 24- 30-inches.

He says the Cleveland sandstone’s clear grain has made the job easier for his carvers to carve but the sandstone, like all sandstones, is still “very abrasive” causing metal tools to dull quickly.

Tyrrell adds that it wasn’t just original elements on the cathedral that required replacement. On the north tower finials reproduced with Indiana limestone years ago were deteriorating faster than the original sandstone.

As of mid-February, the scope of work for Traditional still wasn’t final. A decision was yet to be made on whether the spires at the bell tower should be entirely of sandstone or only partially and capped in bronze and metal to minimize costs and weight on the roof. “The challenge is that the spires have to be heavy enough though to withstand the winds.”

Calling his company one of the largest remaining carving shops in North America, Tyrrell says he has employed eight carvers and two apprentices on the project. “All of the work is unique. There is very little repetition.

“It’s the type of work we like doing, not only because of the carving but also the detective work required to source material and find archival drawings. In some instances where elements are missing and there were no original drawings that showed those details we had to try and get into the head of the carver that did the work the first time.”

The project is scheduled for completion this summer.