Stanford Deck Skylights Get Extreme Makeover
By: Heidi Y. Granke, AIA
Original Project Conditions and Goals
The original problem, which this project corrected, was water infiltration into the below-ground restroom building. The existing conditions included a porous concrete deck and porous brick masonry walls. The existing roof structure is a concrete deck, which had an approximately 1 ½” shallow concrete topping. Water was absorbing into the concrete and seeping into the restroom below. The task of waterproofing the building was achieved by injecting the walls with Hydro Active Injecto Grout by de neef Construction Chemicals Inc. and by adding an Elasto Deck 5500 waterproofing
membrane onto the deck.
Stanford original deck installation
Other constraints on the project included: requirements to match the grade level along the arcade, existing stairs and curbs at grills in adjacent buildings, no water could drain over the arcade and the finished appearance needed to match as closely as possible the existing appearance. The grade at the arcade is only about 1” above the structural slab over the bathroom.
Original Topping Installation
There were several issues related to the topping installation. First, the polymer topping is more difficult to work than typical concrete topping. The polymers, aggregate, and fibers in the mix make it stiffer. Second, the polymers in the mix and the shallow depth make the topping set up more quickly than standard concrete. Third, the topping was installed by a roofing installer not familiar with working with polymers. The result was an uneven slab that had low spots with minor ponding. Another issue was the perceived wetness of the topping. A sealer was applied over the topping to prevent dirt infiltration, which also increased the water repellency of the topping and made the topping look shiny. The wet appearance of the slab was perceived as slippery. However, the aggregate in the topping and the sandblasted finish provide a surface with good traction, even when wet.
Skylights
The project team decided to try to repair the skylights to insure that the entire deck system was watertight. After looking into several different methods and possible suppliers, it was decided to send the skylights to Circle Redmont for revaluation and repair or replacement. Circle Redmont determined that the cast-iron pans were severally corroded under the concrete topping and therefore recommended replacement over repair. HDCCO sent a sample of the concrete topping to Circle Redmont for them to match the color. D. M. Figley sent the topping materials for Circle Redmont to test and consider for use in the skylights. They had difficulty with the polymer topping mix cracking when it was sand blasted. Therefore, they decided to use their own proprietary mix instead of the Exel-crete. Multiple samples were sent to the project team for review until the sample was approved. The final sample was approved on October 29, 2009. The skylights were reviewed on site on December 15. They were installed on December 23, 2009.
Topping Repairs
In 2009, as the project repairs and the skylight installation are being planned, the project team once again reviewed the topping materials. At the July 14, 2009 meeting, Sapna expressed concerns about the polymer slab because of the testing that was conducted by the skylight manufacturer., Circle Redmont. Circle Redmont found the polymer concrete unsuitable for installation in the skylights because the material cracked when sandblasted. Therefore, the types of materials and possible combinations were again reviewed; including a few options not previously review.
The final decision was to re-top to the slab with the same material, but to apply it in small controlled areas so that it could be worked more easily.
Stanford new deck
Final Testing
Hathaway Dinwiddie tested the deck and skylights for water tightness and drainage on December 29, 2009. At 9 am the deck was flooded with water and was monitored every hour throughout the day to insure that there were no leaks. The weather was 51 degrees Fahrenheit at the beginning of the day and the high for the day as 56 degrees. The day was mostly overcast, so little or no direct sunlight fell on the deck. The deck and skylights performed well: there were no leaks and the deck drained
properly. Attached are the hour by hour photographs of the testing.
Stanford new deck watertest
Conclusion
The project accomplished the primary goal of making the restroom water tight.
Stanford bathroom underneath
