Western Specialty Contractors’ St. Louis Branch recently completed a project to restore and waterproof the roof of the Museum of Westward Expansion located beneath the iconic Gateway Arch on the St. Louis Riverfront. The work is part of a multi-phase project, spearheaded by 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 to 18 inches of sod and sandy soil, 10 to 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 was 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 SF horizontal lid and 37,000 square feet of the 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 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 Arch leg, 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. 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 Company. Family-owned and operated for 100 years, Western Specialty Contractors is the nation’s largest specialty contractor in masonry and concrete restoration, waterproofing and specialty roofing. Western is headquartered in St. Louis, Missouri, with more than 30 branch offices nationwide. Learn more at westernspecialtycontractors.com.

This article originally appeared in our July 2017 issue.

Workers prepare to add waterproofing material to the concrete roof. (Photo courtesy of Western Specialty Contractors)