PRESERVATION TECH NOTES     HISTORIC GLASS NUMBER 2

		Figure 11. Just prior to installation, each panel was lifted by hand from the back of a truck and stacked on the sidewalk.

Reinstallation
The reinstallation of the panels at 552-554 Broadway was straightforward because the substructure that supported the vault lights and saddles had been reinforced with steel members approximately seven years earlier (see figure 11). Where leaking panels had led to the deterioration of the original stringers and support structure, the previous contractor shored up the substructure by replacing the deteriorated stringers with cast-iron T-beams spaced beneath each joint between adjacent panels (see figure 12). Additionally, newly cast frame sections were bolted together and installed beneath the sidewalk surface. As part of the current restoration, the contractor examined the substructure at 552-554 Broadway and determined that the previously rebuilt assembly did not require additional strengthening or modification.

To reinstall the panels, a bead of flexible polyurethane caulk was applied around the perimeter of the support frame. The panels were positioned on top of the sealant, in the same order they were set before removal, ensuring that the bolt holes would align (see figure 13). Four stainless steel flat-headed machine screws secured each panel to its framework. A flexible foam backer rod was inserted into the seam around each panel filling much of the gap. The same grout that was used to seal the glass lenses was also applied to the top of the backer rod to form the final surface seal. Again, excess grout was carefully cleared from the joint. The last step was to touch up paint on any area that was scratched during transportation or reinstallation.

Figure 12. During the installation, each panel was set onto T-beams spanning the vault. A steel support girder, running perpendicular to the beams, is visible within the vault opening.	Figure 13. The restored and reinstalled panels before bolting them to the frames, before the final caulk, backer rod, and grout were applied, and before painting the saddles.

Evaluation and Project Data

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