Contractors Restore and Waterproof the Roof of the Museum of Westward Expansion

Western Specialty Contractors work to restore and waterproof the roof of the Museum of Westward Expansion located beneath the Gateway Arch on the St. Louis riverfront.

Western Specialty Contractors work to restore and waterproof the roof of the Museum of Westward Expansion located beneath the Gateway Arch on the St. Louis riverfront.

Western Specialty Contractors, St. Louis Branch, has completed a project to restore and waterproof the roof of the Museum of Westward Expansion located beneath the Gateway Arch on the St. Louis riverfront. The work is part of a multi-phase project, spearheaded by the non-profit organization, CityArchRiver Foundation, to expand and renovate the underground museum, plus renovate the grounds surrounding the arch.

Work on the 100,000-square-foot existing museum roof started by removing 16-18-inches of sod and sandy soil, 10-28-inches of Elastizell engineered fill and the existing waterproof membrane down to the structure deck using a bulldozer and air scrapers.

Once the roof was exposed, Western crews went to work identifying and repairing leaks in the existing museum lid that had been present for many years, as the existing waterproofing had exceeded its lifespan. Several methods were used to evaluate the condition of the concrete roof, which included a chain-drag sounding survey for the structural concrete deck, along with visually identifying delamination and cracks.

Western crews then installed a 2-ply Laurenco modified bitumen sheet waterproofing covered with WR Meadows PC2 protection board. An electronic leak detection system followed by a permanent leak detection grid system were installed over the protection board. Crews then installed a layer of 1-1/2 60 psi Dow extruded polystyrene with an additional layer of WR Meadows PC2 protection board and a J-Drain 780 drainage mat.

The next phase of the project involves waterproofing the 42,000-square-foot horizontal lid and 37,000-square-foot vertical walls of the museum addition. Western’s scope of work includes installing 2-ply Laurenco modified bitumen sheet waterproofing covered with WR Meadows PC2 protection board, and installing an electronic leak detection system, along with two layers of 1-1/2-inch 60 psi Dow extruded polystyrene. A layer of 1.5-inch 60 psi Dow extruded polystyrene is being installed on the vertical walls and a J-Drain 780 drainage mat on both the horizontal and vertical walls.

Additional waterproofing of the north and south museum entrances (approx. 13,800-square-feet), which includes approximately 5,000-square-feet of deck around each leg of the arech, was completed in Spring 2017.

“The museum was largely operational during construction and a lot of the time Western crews were working over occupied space,” says St. Louis Branch Manager Carter Pogue. “Western sequenced the removal of existing roofing material so that they could remove, clean and install new roofing material daily to keep the museum dry during construction.”

Testing was a daily requirement during the waterproofing installation. Western was required to complete a pull test every 500-square-feet and take moisture readings every 100-square-feet. Daily observation reports had to be completed during the waterproofing application, with all testing results and location tests documented along with weather conditions.

Additionally, Western crews took 50 photos daily to document the testing and work area.

The general contractor on the project is McCarthy Building Co.

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