7 INNOVATIONS IN SECONDARY DRAINAGE SYSTEMS

Transcription

1 7 INNOVATIONS IN SECONDARY DRAINAGE SYSTEMS K. F. YAROSH Dow Corning S.A., Parc Industriel-Zone C, B-7180 Seneffe, Belgium SUMMARY: This paper will review innovative internal backup secondary drainage systems for building exterior above grade panellised cladding systems consisting of Architectural Precast Concrete (APC), Composite Architectural Precast Concrete (CAP), Glass Fibre Reinforced Concrete (GFRC), and Stone on Truss Frame (STF) assemblies. The drainage systems design is intended to control incidental moisture, minute leaks and condensation and provide temporary protection to building interior until damaged cladding or exterior sealant joint can be identified and repaired. The systems use pre-engineered silicone rubber extrusions and cast silicone accessory pieces in a unique system designed to collect and control water entry. High-performance silicone sealants are used to seal and structurally attach the secondary drainage systems to the interior surface of the cladding system. Keywords: glassfibre reinforced concrete, installation guidelines, moisture, precast concrete, secondary drainage systems, silicone sealants, stone on truss frame assemblies, walls, workmanship, INTRODUCTION Today, there is an increased emphasis on the need for watertight buildings. Building owners and their exterior wall consultants are requiring that building joints not only have a primary but also a secondary means to prevent and control the penetration of water through the exterior skin of the building. They are also requiring that condensation on the back of the panels be contained and channelled to the exterior of the building. This increased need to control moisture is being motivated by the need to reduce the risk of lawsuits. Certainly, recent lawsuits related to mould issues have increased awareness of moisture-related problems. For most high-rise residential and non-residential construction, sealant joints play a primary role in preventing water and air intrusion. Workmanship becomes critical to ensure watertight buildings. The type and quality of sealants selected will also affect the long-term performance of a building joint. Sealants cannot prevent water penetration through a wall and condensation on the backside of a panel. Variables, such as the atmospheric conditions, location and type of vapour barrier, will affect the amount and rate of moisture condensation on the backside of a panel. When sealant joints are deficient or moisture migrates through a wall and collects behind the wall, untold damage to the structure can occur. Percolation, which is caused by differential pressure between the interior and exterior of the building, can increase GRC 2003: Proceedings of 12th Congress of the GRCA, October 2003, Barcelona, Spain. Edited by J.N. Clarke and R. Ferry. The Concrete Society, Century House, Telford Avenue, Crowthorne, RG45 6YS, UK, on behalf of the GRCA. Ref: GRC21, ISBN X. GRC 2003 Paper 7: page 1

2 the inward flow of moisture into the building. The type of damage that may occur from moisture penetration includes corrosion of structural anchors, damage to interior finishes and floor coverings, loss of insulation efficiency, and mould growth. All of these detrimental features of water damage will reduce the value of the property and make it less appealing to tenants. TERMINOLOGY To assist the discussions in this paper, several common terms will be reviewed: Incidental moisture Defined as condensation or inherent moisture through the cladding or sealants due to undetectable imperfections in material or workmanship. Typically the leaks or condensation are so insignificant that the incidental moisture is absorbed by the substrate and dries before any damage occurs. If this incidental moisture content exceeds the threshold saturation capacity of the substrate, significant uncontrolled water may lead to interior damage to the building as well as mould growth. AAMA For American Architectural Manufacturers Association specifications, water leakage is defined as any uncontrolled water that appears on any normally exposed interior surface, that is not contained or drained back to the exterior, or that can cause damage to adjacent materials or finishes. Water contained within drained flashings, gutters and sills is not considered water leakage. The collection of up to onehalf ounce of water (15 ml) in a 15-minute test period on top of an interior stop or stool integral with the wall system shall not be considered water leakage. Percolation When leaks occur, the damage caused to the building can be further amplified due to percolation. Percolation occurs when sustained high winds or a positive external pressure due to the HVAC system can vacuum water through the damaged sealant joints or cladding. The water will bubble or percolate and blow into the building. DISADVANTAGES OF EXISTING SECONDARY DRAINAGE SYSTEMS For many years, one solution to water penetration was to install two lines of sealant in the joint. One sealant joint would act as a back up should the first joint fail. Some double joint designs use the interior seal as the primary seal and the exterior seal would act as a secondary seal or rain screen. The interior joint would be tapered into the exterior at floor slabs to allow water collected between the joints to weep to the exterior. Air pressure is controlled or compartmentalized to reduce the percolation effect. This is also often called a pressure-equalized system. Though rain screen or pressure-equalized double joint systems can be very effective, they do not address the potential for water penetration through a panel. Secondary drainage systems comprised of galvanized or stainless steel gutters have been used on buildings in the USA in the 1980s and 1990s. These systems have been found to be difficult to install. The systems require power-driven fasteners to install and the systems are difficult to install behind columns. Metal seams are difficult to reseal and panel irregularities and returns make metal gutter systems impractical and GRC 2003 Paper 7: page 2

3 costly. Sheet metal forming, connecting and cutting is difficult. Hand safety becomes an issue due to the difficult handling characteristics of these materials. Gutters can also easily fill with construction debris and the system can become ineffective. In the mid 1990s, building complexity made it difficult to use metal gutter systems. Materials such as plastic, neoprene and natural rubber were used to develop secondary drainage systems. Compatibility and fire resistance concerns arose. Finding adhesives that provide long-term adhesion of these elastomeric gutter systems to the panel was found to be unachievable. From this initial inquiry into organic rubbers for use in secondary drainage systems, silicone was first evaluated as a material for this purpose. Development of the new innovative secondary drainage system discussed in the paper occurred. Once the system was developed and successfully passed testing at Construction Research Laboratories in Miami, Florida, commercialisation of this new secondary drainage system in the United States began. DESCRIPTION OF THE INNOVATIVE SECONDARY DRAINAGE SYSTEM The innovative secondary drainage system that is discussed in this paper is installed as a back up to barrier wall construction composed of precast concrete, glass fibre reinforced concrete, and stone on truss panel systems used in commercial construction. The secondary drainage system is a system of horizontal gutters applied on the backside of spandrel panels designed to collect any condensation and water that collects and falls down the back of the panels. The system has a slope built into it that allows collected condensation and rainwater to drain out through engineered valve boxes placed in the exterior vertical sealant joints. The gutter as designed has a mass of 0.5 g/mm (0.34 lb/ft) of length. If the gutter were to be full of water, the gutter would weigh 1.0 gm/mm (0.68 lb/ft) of length. The structural silicone adhesive used is designed to support the weight of the gutter full of water without having any long-term negative impact on the bond. The innovative secondary drainage system consists of extruded silicone rubber gutters, and moulded parts that are part of an engineered system that allows water to be effectively routed out of a wall system if the primary barrier wall is breached. The extruded silicone gutters are attached with RTV neutral cure silicone sealants to the backside of precast concrete, GFRC, or natural stone. Silicone sealant is also used to attach the silicone gutters, tubes, splices and valves together. Because the system is designed with 100% silicone rubber, the system is expected to provide long-term performance in the spandrel environment. For compatibility purposes, silicone sealant is used as the primary weatherseal joint sealant on the exterior of the building. Figures 1 and 2 are general schematics of the secondary drainage system design. Benefits of the innovative secondary drainage system This innovative secondary drainage system provides numerous benefits to the end user. 1. The system can be field or plant installed with minimal impact to a manufacturer s current operation. 2. The system is flexible and easy to install with no power tools required. The system is installed to the back of the panel with a one-component RTV silicone sealant. 3. The system is easy to keep clean, maintain and quality control after installation. GRC 2003 Paper 7: page 3

4 Figure 1 Figure 2 GRC 2003 Paper 7: page 4

5 4. The system is inherently flexible and can be applied on irregular surface. Sealants will accommodate surface irregularities. 5. The system can accommodate an unlimited variety of joint width and panel dimensions and returns. 6. Better protection and more cost-effective than a second line of sealant. 7. Protection from field construction debris so the system will remain functional and have redundancy despite entry of debris into the system. 8. Non-combustible as defined in ASTM C1115 and compatible with exterior silicone sealants. 9. Non-conductive to mould growth should moisture get in the system. Silicone inherently does not support mould growth. Ability to check performance from the exterior after installation. 10. Provides drainage to the exterior of the wall assembly for any water that enters at the horizontal or vertical joints and controls incidental moisture and condensation. 11. The system minimizes consequential damages and provides temporary protection to the building s interior until the damaged exterior sealant or cladding system can be identified and repaired. COMPONENTS OF INNOVATIVE SECONDARY DRAINAGE SYSTEM The innovative secondary drainage system consists of engineered silicone extrusion, tubes and joint protection collection reservoirs with one-way valves (JPCROV) that are adhesively attached to the back surface of the concrete or stone panels. The JPCROV is designed to prevent percolation and allows a one-way flow of water out of the system. The silicone materials are compatible and marry intimately into the exterior architectural silicone sealant joints. Gutters have a unique design that is resistant to jobsite debris that can accumulate and clog the drains. The following illustrations show the different components of the system. Collection channel. Channel connector. End cap. GRC 2003 Paper 7: page 5

6 Joint protection collection reservoirs with one-way valve (JPCROV). Joint protection collection reservoirs with one-way valve (JPCROV). Tubing/coupling. Secondary drainage system components. GRC 2003 Paper 7: page 6

7 RECOMMENDED INSTALLATION GUIDELINES Following are general guidelines on how the secondary drainage system should be installed: 1. The system should preferably be located above the floor line so that it is above the fire stop between floors and as close to the floor as possible to maximize coverage. 2. As an alternative, if below the floor line and above the window system, evaluate using a flashing system to allow incidental water to pass from one floor to another into a gutter at the head of the window system. 3. The drainage system can be placed onto concrete panels that may reach 9 m (30 ft) in width. 4. For most applications a JPCROV is placed for every 60 ft (30 ft each way) of collection channel C length maximum. This arrangement more than exceeds any incidental moisture or condensation and thus provides some protection against catastrophic failures. The safe capacity of the small JPCROV is 3 gallons per hour. 5. A 9 mm (3/8 ) bead of sealant continuously extruded on the backside of the gutter pressed into the concrete panel will result in a minimum of 12 mm (1/2 ) of continuous contact. 6. The sealant adhesive is used to adhere the components of the system. 7. Finally, remove release liner to ensure that the gutter does not accumulate debris during construction. Components are sized. Sealant adheres channels and tubing. JPCROV viewed from exterior. Removal of release liner from channel. GRC 2003 Paper 7: page 7

8 Condensation of back of panel. Water weeping through JPCROV. BENEFITS OF SILICONE CHEMISTRY Critical to the performance of this new innovative secondary drainage system is the chemistry of the system. The silicone technology used in the production of the channels, valves, coupling and adhesive has excellent resistance to alkalinity, moisture, heat and humidity expected in the environment behind the wall cavity. Silicone rubber has stable physical properties in temperatures from 40ºC ( 40ºF) to 150ºC (300ºF). Silicone has been used as weatherseal sealant in concrete construction for over 30 years. The specific silicone sealant used in this system is known by the author to still be performing on concrete structures for over 20 years. A recent study (1) demonstrated that the adhesive sealant used in this system has excellent performance to concrete when the system is installed as recommended by the sealant supplier. This study evaluated the sealant as an adhesive between GFRC and the rubber used in the system after exposure to various heat and humidity conditions similar to that of a spandrel environment. The results of this study supported the application. Silicone chemistry is the appropriate chemistry for the demanding requirements of this new innovative secondary drainage system. SUMMARY This paper has presented a new innovative secondary drainage system for precast concrete, GFRC and stone on truss construction. This engineered system offers unique benefits over previously offered secondary drainage system. The successful performance of this system is dependent on the robust performance of the silicone rubber and sealants used in the system. REFERENCE 1. CARBARY L.D. and RYAN M.W., Secondary drainage system for architectural panel systems, Symposium on Durability of Construction Sealants and Adhesives, ASTM STP 1453, Andreas T. Wolf, Ed., American Society for Testing and Materials, GRC 2003 Paper 7: page 8