When the venerable New York Public Library Main Branch at 5th Ave. and 42nd St. in New York City recently renovated 60,000 square feet of dead storage space two stories below grade they faced formidable barriers. Built over the Croton Reservoir and completed in 1911, this Beaux Arts landmark building had underground space with very high moisture conditions. In addition, the introduction of airborne silica dust contaminants was prohibited.
The library is open seven days a week, leaving short overnight windows for crews to work in with very limited physical access. The space houses 2.5 million invaluable research books that need to be safe and accessible and is serviced by a new highly sophisticated computer and motorized archival library stack system that required a perfectly flat floor to operate properly. The environment goal was to create a space that was climate controlled at a constant 65 degrees with 40 percent humidity to protect books and manuscripts that dated back to the 1600s and 1700s.
Traditional methods were not going to work. An extensive drainage network was installed and a moisture barrier was applied. About 20,000 small bags of self-leveling underlayment was proposed to level the space at an average depth of 2 inches to provide a flat, smooth level base for the new rack rail system. Access was through a service hatch in the adjacent Bryant Park and then through a maze of underground corridors that meant it would have taken several weeks to load and remove the bag debris after completion of the floor. The GC faced a dilemma; not enough time in the schedule for a traditional self-leveling underlayment installation further complicated by the zero silica dust mandate and restricted hours that they could work in the space.
New York based Pyramid Floor Covering recommended using the LATICRETE SUPERCAP system. They engineered a solution that solved the dilemma. All the self-leveling underlayment material is mixed outside using their patent-pending computer controlled mobile blending truck that can mix and pump the equivalent of 600 bags an hour, up to 50 stories high. That kind of volume and power was more than enough to reach and self-level the slab. The only thing that snaked through the subterranean space was a hose. The SUPERCAP system had a small exterior footprint and provided a simple, unobstructed delivery of the self-leveling product.
The GC had decided small bags were part of the problem. The cementitious calcium aluminate SUPERCAP product arrived in 2,300 pound super-sacks, it has inherent self-drying properties that gains early high compressive strength and ultimately can reach over 5,000 psi. Trades can work on it the following day. Most importantly it provided stability and met the new rail system flatness specifications perfectly. The project supervisor said, “The results were fast, flat, dry and no silica dust inside or outside. No one else can do what they did. This is what we all need to solve problems, save time and comply with the new OSHA silica dust ruling to keep our people safe.”
