Track 3: DELIVERY – INTERVENING INTO HISTORIC PLACES / Volet 3 : Réalisation – Intervenir dans les lieux historiques

Balancing Principles with Practice in the Conservation of 375 year old Masonry Ruins

Saturday, October 14
10:45 AM - 12:15 PM

A National Historic Site, Sainte Marie Among the Hurons was a 17th Century French Jesuit Mission to the Huron [Wendat] nation, situated along the great trading route between Quebec City and the Canadian interior via the Great Lakes. The ruins of three original fireplaces dating to 1639 sit within the multi-layered 1960’s reconstructed site and are part of a long-term conservation initiative.

First excavated in the 1940’s the stonework has remained exposed for 75 years in a harsh environment. The introduction of dense cement pointing and capping nearly 30 years ago in an attempt to slow the rate of deterioration only served to exacerbate the condition of the stonework.

While the initial intent was to conserve the ruins with minimal intervention and maximum retention of original material, once work commenced it became clear that the stonework was in such fragile condition, much closer to collapse than was previously thought, that the approach had to be modified from stabilization in-situ, to taking down and rebuilding. Thus, the initial phases of the work concentrated on research, documentation and recording. This latter task involved the construction of mylar frames for the full sized tracing of the stonework in its as found condition.

A demountable bracing system was designed to permit careful deconstruction once the very hard and dense cement was removed. Rigid Styrofoam and bubble wrap were used between braced plywood sheets and the stonework to hold the assembly from collapse as the take down proceeded. Every stone removed from the wall was documented by individual reference that enabled the team to track the location and intervention on the stone.

The take down exercise presented fresh problems, as behind the dense cement facing, the core was simply powdered mortar. However, this condition revealed the broken tails of face stones resulting from the ongoing movement of the wall that could not accommodate the rigidity of the outer face set in cement and the core in lime mortar. In total over 300 stones were repaired using a reversible acrylic resin and stone dust mix.

The rebuild was carried out using hot lime mortars, gauged with small amounts of a pozzolan. The decision to use this mix was based on mortar analysis and the physical evidence of the surviving mortars. The rebuild was completed by re-assembling the mylar frames and resetting stones to their exact original locations. Interpretation of the final appearance was based on careful comparison with the 1940’s photographs and the physical evidence of mortars that were not original to the 1640’s work. The issue of protection and interpretation of the stonework without compromising the visitor experience is an ongoing exercise.

Learning Objectives:

Keith Blades

Keith Blades Consultant in the Conservation of Historic Buildings Incorporated

Keith Blades Biography

Keith Blades commenced his career in the United Kingdom working with the Directorate of Ancient Monuments and Historic Buildings. [Now Historic England]

In over 40 years of practice in conservation he has worked with architectural firms and the Canadian Federal Government, where he set up a team of conservation masons for work on the Parliament Buildings.

He obtained an MA in Conservation Studies from the University of York and for the past 25 years has based his practice on a mix of consulting, teaching and practical work in the field of masonry conservation.


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David Edgar

David Edgar is a British conservator, stone carver and restoration stonemason with 15 years experience working on heritage buildings and monuments - most recently the West Block Rehabilitation Project at Parliament Hill, Ottawa.
David has lectured for the Ontario Association of Architects, The Canadian Association for Conservation and the APT, as well as the Universities
of Carleton and McGill. David has recently started his own company, based near Ottawa: David Edgar Conservation Ltd.


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Balancing Principles with Practice in the Conservation of 375 year old Masonry Ruins

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