Auditors Building Assessment
Washington, DC: 2005
The Auditors Building, built in 1879, sits at the edge of the National Mall in Washington D.C. The strong impact, typical of the Victorian Gothic style, was created through the juxtaposition of the black mortar joints against the red bricks, darker bands of brown sandstone, decorative terra cotta, and the painted woodwork. The facade is a dramatic play of material, textures and colors, having distinctive tight joints pointed with heavily-pigmented black mortar.
The GSA had called in a construction crew to deal with bricks that had been coming loose from the building, causing a potential "life-saftey" risk. Before this, the skyward-facing joints at the projecting bands of bricks and the parapets had gone 125 years without maintenance. Because it had been so long since the brickwork had been tended to, the government anticipated the need for a "100% repoint." At the time, the funds were not available for such a huge undertaking, which meant that repair of the building could be put off even longer.
But the problem was not only a monetary issue. The GSA preservation staff recognized that the narrow joints would be a challenge for modern mason and their tools to repair, so they required a conservator to be involved in the project design from the beginning. We were brought in to assess the cause of the failing mortar among other failures on the facade.
It was clear that failing mortar was to blame for the loose brickwork, but we need to discern the cause of the mortar failure. We examined a mortar sample and found that the deficiency was a result of the amount of pigment loading required to achieve such a strong black. During the construction era of these buildings, carbon black was commonly used as a pigment. These pigments tend to be much less stable than the iron oxide pigments we use today. This skewed the binder to cement ratio and caused the pigment and lime to separate too easily. The skyward facing joints had been subjected to significant water intrusion, which caused the already compromised mortar to suffer frost-jacking damage and to wash out onto the brickwork below. Despite the mortar's inherent deficiency, our findings showed that a surprising amount of original mortar could be saved, there fore reducing the scope and cost of the project. For the areas that had eroded or washed out we could create a replica mortar that was visually identical, but more durable than the original.
Other issues included discoloration of some brickwork, and huge vertical cracks in the facade. The sulfate-crusting on the joints and stones was probably due to the use of high-sulfur fuels such as coal, common during the early years of the building's life. Although there has been sharp reduction in the use of coal use in the States, the initial damage had already been done. The cause of the cracks was linked directly to the construction period of the late 1870s. Auditors' was built relatively early in the use of concrete slabs in buildings, therefore the understanding of thermal interactions was limited. In the winter when the solid, heated, interior slab was expanding, the cold exterior masonry wall was shrinking. This interaction combined with the weak mortar made joint failures inevitable.
With a clearer understanding of the various causes of failure, we could more accurately gauge the extent of the repairs needed. From there we were able to create a timeline and budget that addressed the long-unattended needs of the building while meeting the GSA's available funding, changing an impractical project into a viable possibility.