Concrete Waterproofing Alternatives
Using Crystalline Technology in Existing Buildings
Water leaks often happen in concrete walls in existing buildings, particularly below grade. Of course, that means, the “positive side” (exterior) of the concrete is likely buried and not readily accessible. Hence, “negative-side” (interior) waterproofing is typically undertaken on the inside face of the concrete. Although water may still penetrate the exterior surface of the concrete, with this approach, it will be prevented from reaching the inside surface without impacting the interior of the building or any spaces/functions/materials found there. Of course, protection against concrete deterioration is not achieved as with positive-side treatment, but water penetration stops at the interior side of the concrete so the inner surface is protected. The degree of protection and the effectiveness of the interior coating will depend on the product used. Some are simply painted applications that may hold up for a while but are not guaranteed for more than a few years.
A crystalline waterproofing system was used on the negative-side interior walls of this below-grade parking structure. A fountain complex is located above this garage, which introduces water into the surrounding subgrade.
Crystalline Renovations
The preferred choice for negative-side waterproofing is to use crystalline products that are applied from the inside. These are provided in powder form, mixed with water on-site, and applied as a cementitious slurry coat to above-or below-grade concrete. The intent is to cover the entire inner wall surface and thus create the conditions for the crystalline chemistry to diffuse into the substrate and create a continuous water seal. It can be a single coat or the first of a two-coat application where recommended by the product manufacturer.
Like any field applied product, surface preparation is obviously critical. The slurry coat can be applied to wet surfaces, but the existing wall needs to be intact and stable enough to receive the coating. In some cases, removing loose or damaged pieces may be necessary followed by appropriate repairs. Providing water plugging or other measures for large holes may also be called for. All of these steps require the judgement of a design professional and the skills of tradespersons to do the needed work.
The application of crystalline coatings on existing buildings yields all of the same characteristics as when installed on new construction, plus some other notable ones as follows:
- Wet or dry application: Crystalline applications do not require a dry surface for installation. This is particularly helpful in conditions where dryness would be difficult or impossible to achieve.
- Simplified preparation: Compared to some other alternatives, there is no costly surface priming or leveling needed prior to the application
- Durability: The finished treatment, when installed properly, is not subject to deterioration from either the inside or outside as other coatings may be. Hence there is typically no need to plan on replacing it after several years.
- Cost: Crystalline treatments on negative-side surfaces are less costly to apply than most other methods, particularly over the remaining life of the building.
EXISTING CONSTRUCTION CASE STUDY 1
Project: Gateway Arch Expansion
Location: St. Louis
Designer: Cooper Robertson and James Carpenter Associates
Landscape Design: Michael Van Valkenburgh Associates
Primary Contractor: McCarthy Building Companies
The Project: Soaring 630 feet above the mighty Mississippi River and its St. Louis home, the gleaming stainless-steel Gateway Arch is the centerpiece of the Gateway Arch National Park and a popular attraction that draws more than three million visitors each year. Unfortunately, while the weighted catenary arch itself realized the dream of its designer, Eero Saarinen, when it was completed in 1965, the rest of the 91-acre site fell victim to cost cutting and failed to link the park to the rest of the city as had originally been envisioned.
In 2009, a plan was developed to dramatically expand and redesign the landscaping and facilities around the base of the Gateway Arch to integrate it more fully with downtown St. Louis and provide the visitor experience befitting one of the world’s greatest monuments. The largest public-private partnership (P3) investment ever in a national park—known as the Gateway Arch Park Foundation—was formed to provide $380 million in public and private funding for the renovation and expansion effort.
The multiphase project, which was completed in July 2018, features a 46,000-square-foot addition to the preexisting visitor center and museum, the complete renovation of the preexisting 106,000-square-foot Museum of Westward Expansion, the construction of a 300-foot-wide park extension over an adjacent highway, flood abatement measures, revised landscaping for the 91-acre park, and the renovation of two major plazas that lead west from the park into downtown St. Louis.
The museum expansion was designed by Cooper Robertson and James Carpenter Associates, both of New York, with Trivers Associates, St. Louis. Michael Van Valkenburgh Associates, New York, oversaw the landscape design. McCarthy Building Companies, the country’s oldest privately held national construction company, was the primary general contractor for the Gateway Arch Park redevelopment. The firm constructed the new 46,000-square-foot visitor’s center and museum extension, and oversaw the transformation of the north and south grounds. The St. Louis branch of Western Specialty Contractors (WSC) was subcontracted to waterproof the roofs, walls, and floors of new and preexisting structures throughout the four-year project.
The Challenge: The new entrance to the park features curving pathways around a pond that allow visitors to gradually descend below grade level into a luminous space. Previously, visitors entered at the base of either arch legs and could easily skip the museum and gift shop on their way out. Now, visitors are treated to an immersive experience even before they reach the trams to carry them to the top of the arch.
Built below the publicly accessible level of the new visitor center is a network of mechanical tunnels, measuring 12 feet high, 14 feet wide, and running a total of 550 feet. The tunnels carry various utilities, including steam and electrical lines, and provide pathways for employees to traverse the facility without entering public spaces. The tunnels also provide the base pits for several elevators, a stairwell, and two escalators.
WSC’s St. Louis branch assisted McCarthy in the preconstruction bid preparation process. The architect indicated that crystalline waterproofing should be applied to the interior walls and floors of the mechanical tunnels. The outer walls, but not below the floor, would also be waterproofed with an asphalt membrane.
The Solution: WSC, a member of Local No. 2 of the United Union of Roofers, Waterproofers, and Allied Workers, has had extensive and successful experience in the use of crystalline waterproofing products in projects nationwide. “The specification we received noted that a crystalline waterproofing product should be used on the interior of the tunnels, and it named three products; however, only one was applicable to our project,” explains Thom Belgeri, senior department manager, WSC St. Louis branch. “We were very familiar with the product and knew it would work well for this application. It was really a no brainer.”
WSC worked in small crews to apply the waterproofing products to nearly 20,000 square feet of interior tunnel surfaces. “Other contractors needed access to the tunnels so we had to kind of work around some of the other trades,” Belgeri says. “We would apply the crystalline brush-on coating for three or four days, and then take a short break while other workers finished their jobs. Working in that way, it took about a month to do the whole thing.”
Both a concentrate and modified slurry mix were crystalline treatments used for waterproofing and repair of the existing concrete. WSC crews mixed the crystalline products with a drill mixer in 4-gallon batches and scrubbed it onto the floors and walls of the tunnels with stiff brushes. One worker would power wash the next area of the tunnel to be waterproofed, while three to four other workers applied the crystalline waterproofing.
Along the joints where the tunnel walls met the floor, the concrete crew formed a 1-inch by 1-inch channel (i.e., block-out) in the newly poured concrete to allow WSC to install a dry-pack mix of crystalline waterproofing compound into those critical joints for extra protection. The dry mix was tamped into the joints with a wood block and hammer to provide extra protection at these vulnerable joints. (A pneumatic packer may also be used for this purpose.) A second coat of crystalline waterproofing slurry was applied over the base layer too as a reinforcement. This is done in applications where a second coat is recommended.
Results: A two-coat application of crystalline waterproofing slurry was also used by WSC to waterproof four 60-foot-long by 2-foot-wide concrete trench drains at grade level, as well as hundreds of feet of arced knee wall used around the new circular entrance that welcomes visitors to the expanded and renovated Gateway Arch National Park.
“Our branch specializes in new construction waterproofing and roofing,” Belgeri notes. “We have two other groups in St. Louis that specialize in concrete and masonry restoration. We all use crystalline concrete waterproofing products extensively. We used it a lot for applications just like the Gateway Arch project— tunnels and elevator, escalator and stairwell pits. Anywhere, usually below grade, that needs extra protection. General contractors are the toughest critics. The goal is no callback from the GC, and that is what we get with crystalline concrete waterproofing.”
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