Building Overview
- The Grand Coulee Dam in Northeastern Washington, at 550 feet high and a mile long, is the nation’s largest hydroelectric power supplier. Four powerhouses provide 21 billion KW hours per year to feed an 11-state Western power grid. Just one of the dam’s 33 generators can power a city the size of Seattle.
The Challenge
- After 30 years of service, the 120,000 square foot Spray Polyurethane Foam (SPF) roof of the largest powerhouse was beginning to leak. Birds and severe weather were accountable for most of the damage. The roof consists of nine 120 x 112-foot free-floating concrete panels with expansion joints, covered with SPF up to 12 inches thick. Damage to the SPF roofing was substantial, but not consistent across the entire roof surface.
Solution
- To restore the roof to specification, BASF’s Elastospray 81305 three-pound closed-cell spray polyurethane foam was used. Tapering the foam thickness from the roof’s center line to the outside edges provided drainage. Consecutive passes of United Coatings’ Elastuff® 101/102 polyurethane coating systems were then applied to create a tough, 60-mil thick elastomeric membrane that is bird and weather resistant. The original contract was to remove six inches of foam and then prime and spray-apply a single 1.5-inch pass of BASF’s Elastospray 81305 three-pound closed-cell polyurethane foam. Multiple passes of United Coatings™ Elastuff® 101/102 polyurethane coating system would create a 60-mil bird-resistant barrier atop the fresh foam. Further inspection revealed that some of the panels of the existing foam needed to be completely removed down to the bare concrete.
Key Facts
- There was only one access point to the roof, requiring the work crews to climb an 85-foot stairwell located at one end of the 1,000-foot-long building. All equipment and supplies were lifted onto the roof using a temporary crane. Weather conditions dictated that the application work be done from July through October, requiring the project to be completed over a two-year period.
