Published: Jan 2004
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In conjunction with the exterior cladding system, field applied architectural sealant joints are the primary source of resistance against air and water intrusion on most high-rise residential and nonresidential commercial structures. Jobsite practices and quality in workmanship will dictate deficiencies in application of the high performance sealants specified for this purpose. When these deficiencies allow water and air to enter the structure, or when water condenses and collects behind the walls, damage caused by water is detrimental to the structure. The condition known as percolation, where outside positive pressures associated with Heating Ventilation and Air Conditioning (HVAC) systems in combination with wind driven rains literally vacuum water into the building, further amplifies this problem. The damages attributed to water and air infiltration can be corrosion of structural anchors, reduction in insulation efficiency, damage to interior walls, damage to floor coverings and mold growth.
This paper reports on the design, development and testing of a state of the art secondary drainage system that is used behind prefabricated panelized Glass Fiber Reinforced Concrete (OFRC), Architectural Precast Concrete (APC), Composite Architectural Precast (CAP), and natural stone on truss systems.
This system consists of silicone extrusions, tubes and joint protection collection reservoirs with one way valves (JPCROV) that are attached to the back of the concrete or stone panels using adhesive attachments, which are compatible and marry intimately into the exterior architectural sealant joints. Unique designs of gutters that are resistant to jobsite debris that can clog drains and render them inadequate are presented along with the JPCROV that prevents percolation and allows water to weep out of the system These additional materials within the wall cavity also must have benign fire properties due to the concern for toxic gasses and smoke in the event of a fire.
The technology of the silicone extruded gutters, tubes and percolation boxes is most suitable for the alkaline variable temperature and humidity environment found in these wall cavities. Silicone adhesive technology of one-part neutral cure RTV silicone sealant is used to mount the secondary drainage system within the wall to provide a long-term performing solution. Durability data is presented on the bonds between the silicone extrusions and concrete substrates for this application. Modified ASTM Standard Test Method for Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens by Tension Loading (Metal-to-Metal) (D1002-99) data after room temperature cure, water immersion, and both elevated temperature and high humidity is presented as data simulating the actual application. System design capacities and proper installation for maximum coverage are also presented.
exterior cladding, infiltration, drainage system, silicone extrusion, durability, ASTM D1002
Associate Industry Scientist, Dow Corning Corporation, Midland, MI
Chief Estimator, Clark Pacific, West Sacramento, CA