Waterproofing for plaza decks

Building a new plaza deck is complicated, but renovating an existing project brings additional challenges. There are the usual difficult logistics required to complete a project when a space is occupied. Often, the deck itself needs repairs, which is difficult to accomplish without removing the wear surface and violating the waterproofing system. Perhaps it was not built properly, has suffered excessive wear, or no longer meets the changing needs and priorities of the owners.

This was the case with the 1860-m² (20,000-sf) plaza deck linking Scottsdale Fashion Square offices with the eponymous shopping center—the largest in Arizona. Positioned at the highly visible northwest corner of Scottsdale and Camelback roads in downtown Scottsdale, the original 1989 post-modern office building and deck needed to be freshened up to befit class-A office space.

The architect for the project, Gensler, integrated the six-level building and deck by harmonizing design details and “creating a consistent design language for the entire development,” said John R. Williams, AIA, associate.

It was also an opportunity to add a layer of waterproofing where there was none previously. (This was the norm for dry-climate areas, like that of Scottsdale, several decades ago.)

The deck, which shelters parking below, was also in need of some minor repair. Water was trickling through areas around the existing planters and vents.

“This is the kind of thing that just gets worse,” said Brian Whited, partner at AK&J Sealants (Phoenix, Arizona), subcontractor for the project, which was run by A.R. Mays Construction.

Care was taken to avoid hitting and damaging the post-tensioned deck’s tendons throughout the project. A peel-and-stick waterproofing was added to the edges of the garage, where accessible.

The architects and owners selected a cold-applied polyether waterproofing that could be rolled, troweled, or squeegeed onto the surface and emit next to no odor—important for occupied spaces. The proprietary material also functions as waterproofing for the planters. Since it can be lapped up the wall several inches above the topmost layer of the overburden, it serves double duty as a flashing.

Edges, cracks, joints, and corners of the deck were first protected with a layer of mesh embedded in polyether. A 1525-µm (60-mil) basecoat was applied, then a layer of spun-polyester reinforcing fabric. This helps prevent cracks in the substrate from telegraphing through, while adding overall strength. A second coat of the same thickness followed, for a total of 3050 µm (120 mil).

An asphalt-sheet protection course was added over the waterproofing, and drainage board was used under the planters. The cold-applied membrane was applied around the inside of the planters and at the base as a root barrier. These areas were not reinforced with fabric.

The deck features precast concrete hardscape in various colors denoting walkways. There are new desert-friendly plantings throughout, a shade structure, and a section of “very realistic-looking” artificial turf, Williams said. The work was done with an eye to creating an event space for the office and mall tenants, and also created a walkway from the street corner in front of the building into the mall. There is now also a loop-through drive for dropping off guests.