Track 2: Materials over Time: Points of Change

General Abstract

Finding Paskapoo: A Lesson in Stone Sourcing – Finding a suitable match when the original is no longer an option

Tuesday, September 25
8:30 AM - 10:00 AM
Location: BNCC- 101BG

In response to a requirement for fire resistant building following the Calgary, Alberta Fire of 1886, distinctive yellowish-buff sandstone, Paskapoo, was locally quarried from outcrops in the Calgary area. The sandstone was used in many landmark buildings, including Calgary City Hall, and many buildings along Calgary’s main street, Stephen Avenue; Calgary became known as Sandstone City. However, by the early 1900s Paskapoo sandstone quickly fell out of use due to functional and operational problems with quarrying, the fragile quality of the stone, and competition from other stone supply, particularly the Manitoba Tyndall and Indiana limestone.
Calgary City Hall, a national historic site was completed in 1911. This monumental Romanesque Revival Style building clad in Paskapoo sandstone continues to house the offices of the Mayor and city Councillors. As part of the Calgary City Hall rehabilitation project EVOQ Architecture was mandated by Lemay + Toker Architects to act as Heritage Architect. Large expanses of the masonry facades suffered severe deterioration due to weathering, longstanding and repeated saturation, and the fragile quality of the stone itself (The cement is of a calcareous nature and the stone is markedly bibulous – William Parks Report on the Building and Ornamental Stones of Canada, 1915). In fact, testing revealed that the stone is not very resistant to salts and frost. It was clear from the outset that the rehabilitation strategy would consist of preserving and protecting the surviving stone by introducing a water shedding strategy and that the stone that was heavily deteriorated and subject to continued high exposure to water and salts would have to be replaced with a stone, perhaps with better performance but still compatible with the existing Paskapoo. With Paskapoo no longer available, it was critical to find suitable replacement sandstone for the work. As a first step, the outcrops that were originally quarried and survived urbanization were visited and evaluated for reactivation. The second was to conduct an international tender call for stone supply that yielded suppliers from Germany, Spain and the USA. This presentation will briefly present the Calgary City Hall project and the masonry rehabilitation strategy and describe the extensive stone sourcing process which included visits to several quarry sites and buildings. Topics will include: Considerations and challenges in reactivating dormant quarry sites; Establishing compatibility criteria to prepare a call for tender for replacement stone supply; Evaluating candidate quarry sites, capacity and operations; Evaluating chemical, physical and visual compatibility between original and replacement stones including laboratory testing, assessment of field performance in existing buildings, short and long term weathering characteristics; tying it all into a sensible and clear preservation strategy.

Learning Objectives:

Giovanni Diodati, Architect

Senior Associate
EVOQ Architecture Inc

John Diodati is a conservation architect and educator specializing in materials conservation and traditional building techniques. He is a graduate of McGill University’s School of Architecture (BArch 1990) and is a Senior Associate at EVOQ Architecture / FGMDA since 1999. In his over 28 years of practice, John has led teams of multidisciplinary specialists and been in charge of the materials conservation and building envelope on an impressive number of award-wining projects ranging from modest vernacular structures to the buildings of the Canadian Parliament. John served as a board member of APT since 2009 and vice-president from 2013 - 2018.


Send Email for Giovanni Diodati

Peter Wollenberg

Wollenberg Building Conservation, LLC

Peter Wollenberg is a Columbia-trained architectural conservator who began his career in historic preservation in Vermont before attending graduate school. Following graduate school, Peter worked for Geier Brown Renfrow Architects in Washington, DC working primarily on the Historic Structure Reports for buildings in the Federal Triangle. Peter moved to St. Louis and worked for Washington University Technology Associates (WUTA), a company that specialized in sculptural and architectural conservation around the country. He started Wollenberg Building Conservation in 1992 and has worked on projects in numerous states ranging from the repair of small stone sculptures to monuments to the Wainwright Building and the Missouri State Capitol.


Send Email for Peter Wollenberg


Finding Paskapoo: A Lesson in Stone Sourcing – Finding a suitable match when the original is no longer an option

Attendees who have favorited this

Please enter your access key

The asset you are trying to access is locked. Please enter your access key to unlock.

Send Email for Finding Paskapoo: A Lesson in Stone Sourcing – Finding a suitable match when the original is no longer an option