The Building Conservation Directory 2024

116 THE BUILDING CONSERVATION DIRECTORY 2024 CATHEDRAL COMMUNICATIONS By the early 2000s higher power diodepumped NdYAG lasers had started to appear. These could deliver several hundred watts of average power, which meant faster action and opened up the possibility of laser cleaning on a much larger scale. In 2005 the Nickerson Mansion in Chicago became the first building in the United States to be cleaned entirely by laser when a 120W NdYAG laser (1064nm; 5ns) was used to remove a black pollution crust from over 2,500 square metres of Berea sandstone. Since then high-power NdYAG lasers have been used in a number of important projects including both the Jefferson Memorial and the US Capitol building in Washington DC, and the Canadian Parliament Buildings in Ottawa. Over the past ten years we have seen the emergence of high-power fibre laser systems which are compact, easy to move around on site and robust, requiring very little maintenance. The following projects include a range of substrate types (limestone, sandstone, marble, alabaster and stoneware), and cover the cleaning of both sculpture on historic buildings using low-power NdYAG systems, and large areas of stonework using highpower lasers. They have been selected to give the reader a flavour of the kind of work to which laser cleaning is suited. As with all cleaning methods, the quality of the end result depends on understanding the original materials and the soiling, and on the skill and sensitivity of the trained practitioner. CANADIAN PARLIAMENT BUILDINGS, COMPLETED 2017 In a project beginning in 2012, (developed for Public Services and Procurement Canada by David Edgar Conservation with RJW Gem Campbell Inc, EVOQ Architects and PCL Constructors), the West Block at Parliament Hill in Ottawa became only the second building in North America to be cleaned primarily by lasers. Laboratory testing carried out at the beginning of the West Block Rehabilitation Project (WBRP) indicated that they could remove atmospheric soiling acceptably well with less risk to weathered and delicate carved surfaces. As they are also capable of capturing dust and debris at the surface, lasers allowed other conservation activities to happen concurrently, and (with appropriate safety controls in place) in close proximity. This allowed for compressed work schedules. The WBRP Heritage Masonry Contractor employed a specialist team of trained conservators and conservation stonemasons, to ensure that the laser cleaning was part of an integrated conservation approach. More than 13,000 square metres of exterior stonework, of Nepean and Berea sandstones, were cleaned using 500W and 1000W diode-pumped NdYAG lasers (wavelength 1064nm). Such high-power laser systems (originally developed for industrial applications) are robust and durable, and therefore suitable Figure 2: West Block, Parliament Hill (Ottawa, Canada), cleaned by laser between 2012–2017, with the exception of the tower which was cleaned using abrasive means in about 2005 (Photo: David Edgar Conservation Ltd) Figure 3: West Block gargoyle (Berea sandstone) before and after laser cleaning (Photos: David Edgar Conservation Ltd)