In the winter of 2006-07, Structural Preservation Systems (SPS) completed a historic restoration/stabilization project in Washington, D.C. Two historic townhouses built during the early 20th century combined to form the national headquarters for an organization. Both buildings were in need of structural maintenance work. One building consisted of limestone cladding with a brick/masonry back-up wall. The other building consisted of a multi-wythe brick wall with brownstone window sills and keystones.
Initially, SPS was approached to assist in determining the methodology of repairs to secure the structure. The primary focus of the design and construction team was to stabilize numerous flat arches that appeared to be sagging and becoming displaced. It was feared that if the situation was not addressed the arches could continue to displace and fall. Based on this information, it was presumed that the arches would need to be removed and rebuilt with the structural wall inspected and repaired as needed. Additionally, it was also discovered that miscellaneous repointing, brownstone sill repair and rebuild of a section of out-of-plane brick wall were also required.
Upon visual inspection, SPS noted that the mortar joints around the stone in the flat arches that exhibited sagging or moving were either in fair condition, 100 percent failure and non-existent, or some level of deterioration. Because of the varying degrees of mortar joint failure, it was difficult to identify the root cause of the arch displacement. The assumed theories were that the arches were displacing due to one or a combination of the following conditions: failure of the mortar joints which meant the stone were not bearing on each other as originally constructed, failure of the stone attachment to the back up masonry wall or a combination of the two concerns.
Because of the unknown existing conditions, the project direction was in limbo, having a wide range of potential scope, (remove/rebuild vs. other options) yielding highly variable restoration costs. It was up to the project team to determine the appropriate direction of the project and define the scope. In order to obtain valuable information and clarify the scope, SPS suggested a condition inspection via destructive testing.
SPS was authorized to proceed with removal of the mortar joints surrounding the stones at one of the smaller flat arches and visually inspect the existing conditions. At a three stoned flat arch to the left of the main entrance, SPS began by pinning the two side stones with stainless steel, helical wall ties to secure them in place. Next, the mortar joints were removed around the keystone. Once the keystone was freed from any contact with the surrounding limestone it held firm, indicating that it was not bearing on the other stone in the flat arch. Through the removed mortar joints, a boroscope gave visual access behind the stone to reveal a brick structural wall, determined to be muli-wythe and a metal clip anchoring the keystone into the masonry wall.
Based on these observations, the engineer felt it would be appropriate to anchor the stones in their existing positions with helical wall ties to prevent further movement.
Ultimately, SPS pinned up five limestone flat arches and six brick flat arches with stainless steel helical wall ties, removed/replaced all mortar joints in the arches as well as miscellaneous mortar joints on the façade, rebuilt an out-of-plane section of brick wall, patched two exfoliating brownstone window sills and four exfoliating brownstone keystones. All pointing mortar and patching mortar were custom color matched to blend in with the existing coloring of the structure.
Essentially, the project developed from a structural issue to properly defining a value engineered scope of substantial cost savings due to the effective recognition/understanding of project goals and obtaining valuable structural information from an inspection. Upon completion, the structure retained the architectural and historic appearance while the client was pleased with SPS' craftsmanship.