AIC's 45th Annual Meeting

The West Block is one of the three major buildings on Parliament Hill in Ottawa, Canada that house the country's Federal Government. Begun in the 1860's in a Neo-Gothic style, the West Block has been modified and extended with stylistically sympathetic additions including the massive Mackenzie Tower. Conservation Solutions was engaged to specify and oversee the treatment of every one of the hundreds of thousands of stones on the mass masonry exterior during a reconstruction of the building starting in 2012. A team of contractors, architects, engineers, conservators, and masons worked over 4 years to perform the assessment and treatment which was completed in 2016. Other work in the courtyard and interiors will continue beyond that.

After laser scanning of the building and development of a set of treatments for each condition was prepared by the architect and contractor, Conservators began a stone-by-stone survey of each wall. Early in the work, which was based on extensive previous testing, additional tests were performed to ensure compliance with the specified treatments as was as to modify and improve any that could be. Laser ablation was tested and found to be both more effective and efficient at cleaning the sulfate crusts and soiling on the sandstone blocks and was substituted for the originally planned wet micro-abrasion cleaning. This allowed for improved work flow as it was better suited to the challenges of the northern climate's cold winters, as well as reducing water entry into the building and achieving a stone surface with porosity characteristics closer to those of the original stone. This was adopted and became the largest laser cleaning treatment ever performed on a building as a result of this testing. Other work was integrated with more traditional masonry crafts in re-pointing, dutchman and other repairs, and unit stone replacement. Tracking the recommended work on each block and documenting it all to ensure contract compliance and for archive purposes required developing sophisticated technologies that could withstand construction site conditions and readily translate into archive AutoCAD drawings and reports. This paper will present the results of the tests, the means that were developed to address the overwhelming scale of the work, and the successful results of the treatment.