On June 18, 2014, a treacherous storm passed through Bloomfield Hills with wind gusts of up to thirty-nine miles per hour. At some point during the storm, a tree snapped and fell directly onto the Cranbrook House Pergola*, causing significant damage. Much of the original redwood trellis was crushed and two of the column capitals were severely damaged. One of the columns was knocked completely off the wall. In addition, the concrete slab and columns had been deteriorating over time due to water infiltration. Cranbrook was left with an unusable space, directly adjacent to the Sunken Garden.
Reconstruction of the pergola began two years later on June 6th, 2016. The goal was to preserve as much original historic material as possible, while replacing anything that was beyond repair.
The first step in the restoration process was to re-tuck point all the mortar in the stone walls which had deteriorated over time. All the mortar in the joints between each stone had to be chipped out and cleaned before the new mortar could be installed. In various instances when mortar was removed, the stones would become loose. In efforts to hold the stones in place, wood wedges would be inserted to temporarily hold rocks in place. In addition to improving the appearance, the new tuck pointed mortar provided renewed support for the walls, allowing us to remove the floor slab.
Next, the crew removed the existing wood beam (to be reused) and began to systematically demolish the concrete wall caps and columns. The northwest column, base and capital were left in place throughout the project as they were structurally sound. However, the other three columns had to be demolished and rebuilt. Much of the concrete on the inside of the columns was so deteriorated that portions of it could be removed by hand.
Demolition continued with removing the concrete slab which served as both the ceiling for a garden storage area and the floor for the pergola. Demolition of the slab was challenging because the stone walls were built on top of it, as opposed to the slab being poured abutting the walls. The contractor had to leave notches of the slab in place to provide support and prevent the walls from collapsing. Each notch was then very carefully removed and temporary shoring was installed to prevent a cave in.
Next, the crew formed the ceiling/floor and installed rebar so the new structural slab would be much stronger than the original. When pouring the concrete, the crew had to be meticulous to ensure it was evenly placed under all the stone walls and through the cage of rebar.
Once the slab was poured, the crew started building the column forms. Each column’s entasis, or taper, toward the top was achieved by building a wooden barrel that narrowed towards the top. The concrete was then cast directly into the barrel. This process was very similar to how the columns were originally constructed.
As mentioned earlier, one of the beams was salvageable in its entirety. However, the other beam had to be rebuilt with about fifty percent new wood bolted to the older beam. Like the original construction, we used redwood. The contractor replaced all the purlins (or cross beams) with new redwood, using one of the original purlins to recreate the decorative pattern on each end.
After a few finishing touches, the new (and improved) Cranbrook House Pergola was completed. Many thanks to the crew involved in this restoration project, and come check it out for yourself soon!
* Cranbrook Archives was able to determine that the original pergola was intact as early as 1919.
–Ryan Pfeifer, Project Manager II, Cranbrook Capital Projects
Special thanks to Elizabeth Fairman (CKU ’17) for research assistance.