Pre-Cured Silicone Sealant In Metal Building Applications
By Jason Bakus, Sealex Inc.
Pre-cured joint sealant sometimes referred to as “membrane,” “extrusion” or “flexible flashing,” is produced by extruding an elastomeric material and allowing it to cure to a flexible product in a controlled manufacturing environment. Pre-cured joint sealants are packaged in cured form, typically in rolls, and installed using a thin layer of adhesive near the edges to attach the material to the substrate being sealed. With the outer edges adhered to the substrate, the middle of the pre-cured sealant, which is not bonded to the substrate, acts as the area for expansion and contraction. Pre-cured sealants are manufactured in widths ranging from less than 1” to greater than 12”. Examples of pre-cured sealants are shown in Figure 1.
Several basic types of pre-cured joint sealants are used in the construction market today, but silicone pre-cured joint sealant is the most commonly used for several reasons. First, because of its molecular structure and high bond energy, silicone has excellent aging characteristics and is resistant to UV light and weathering. This gives silicone a longer effective life span than organic materials such as EPDM, polyurethane, polysulfide and butyl, which are prone to degradation from UV light. Because silicone does not degrade when exposed to the elements, it is possible to produce the material very thin (1-2 mm). In addition, the movement capability for silicone pre-cured joint sealant can be as high as +200%/-75%, which is significantly higher than other products used in similar applications. The high movement capability coupled with the thin material gives pre-cured silicone sealant the ability to easily handle the multi-directional movement commonly found in metal building applications. Additional advantages of silicones over other materials include a wide operational temperature range and better resistance to color fading.
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Figure 1. Pre-cured Silicone Sealant.
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Figure 2. Pre-cured Silicone Sealant Used to Seal between a New Addition and an Existing Metal Building.
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Figure 3. Mock up of a metal roof expansion joint using pre-cured silicone sealant along with metal cover plates. (Photo courtesy of Building Research Systems, Inc.)
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Figure 4. Mock up of a roof to wall transition application using pre-cured silicone sealant.
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Figure 5. Pre-cured silicone sealant used in a ridge repair application.
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Figure 6. Hole in a roof deck repaired using pre-cured silicone sealant.
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Figure 7. Repair of metal roof using pre-cured silicone sealant.
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Pre-cured silicone sealant has been used for many years in a variety of building envelope restoration applications and has recently (within the past 2 years) begun to be used by some forward thinking manufacturers and erectors in the metal building industry.
There are many features of pre-cured silicone sealant that makes it ideal for a variety of metal building-related applications. First, flexibility and high movement capability makes pre-cured silicone sealant perfect for sealing areas with a large amount of thermal expansion and contraction, a situation commonly found in metal building applications. Secondly, the UV stability of silicone gives pre-cured silicone sealant a long effective life and keeps it from degrading under the intense, long-term exposure to the elements routinely found in metal roofing applications. In fact, silicone sealants that have been in place on building exteriors for over 40 years are still performing well! Figure 2 shows a pre-cured silicone sealant application on a metal roof joint between a new addition and an existing metal building. Because of the UV and weather resistance of this material, there is no need for a cover plate to protect it.
Perhaps the most exciting and ground-breaking feature of pre-cured silicone sealant systems in metal building applications is the fact that they require no mechanical fasteners for installation. The green strength of the adhesive allows the pre-cured sealant to be installed without any other means of attaching the material to the substrate, even when installed on a vertical surface. The effect of this feature is wide reaching. First, the installation of pre-cured silicone sealant systems is quick and efficient, particularly when compared to other systems commonly used in these and similar applications. Other systems, either all metal systems or other “membrane” type systems, generally require many mechanical fasteners, as many as 1500 fasteners per 100 linear feet of material, often in addition to sealants and/or mastics. These fasteners dramatically increase the time and labor cost required for the installation of these systems. In addition, since each and every fastener creates another hole in the roof, the potential for leaks increases significantly. Further complicating the installation process for these other systems is the requirement of an often complicated splice kit to fuse the ends together. Pre-cured silicone sealant systems require only an overlap of the ends of the material and a bead of the silicone adhesive to adhere them together. All these advantages are leading many metal building manufacturers to incorporate pre-cured sealant systems into various applications in their new buildings.
Pre-cured silicone sealant systems are currently being installed successfully in many different applications within metal buildings, including:
• Expansion joints (Figure 3)
• Roof to wall transitions (Figure 4)
• Roof height change details
• Joints between new and existing buildings (Figure 2)
• Ridge applications (Figure 5)
• Pipe and other penetrations
• Roof curb seals
• Many misc. repair applications
In addition to the new construction applications discussed above, pre-cured silicone sealant is commonly used in various repair applications, often in metal roofing. Some of these repair applications include repair of holes in roof decking (Figure 6), repair of failed standing seams and other roofing repairs (Figure 7).
The use of a premium silicone adhesive in the pre-cured silicone sealant system allows the material to be installed to a variety of metal substrates (without the use of a primer) including; Galvalume®, stainless steel, galvanized steel, Kynar® coated, acrylic coated, aluminum and others.
Pre-cured silicone sealant is available in many standard sizes and colors. Manufacturers also offer custom color and custom designed pre-cured sealant to fit an assortment of application requirements. Custom colors can be matched to various metal roofing finishes, allowing the material to easily blend in to the roof system.
Finally, the use of pre-cured silicone sealant can result in a “greener,” more energy efficient building. Most buildings have numerous leaks in the building envelope and therefore they need to be pressurized, resulting in higher heating and cooling costs. Virtually any leak in a building can be sealed using pre-cured silicone sealant. Once these leaks are sealed, the amount of air required to keep a building pressurized is drastically reduced. This results in a significant reduction of heating and cooling costs, making the building more energy efficient.
Because of its numerous advantages, pre-cured silicone sealant is beginning to be used more extensively in various industries, including metal building construction and repair. As leaders in the metal building construction industry begin to realize the impact that cost savings and product performance can make in a wide variety of applications in both new construction and renovation projects, it is expected that the market share for this material will continue to grow.
Jason Bakus is vice president of Sealex, Inc., based in Harbor Springs, MI and has 13 years of experience in the silicone and pre-cured sealant industries. Jason can be reached at jbakus@sealexinc.com or (231) 348-5020. www.sealexinc.com.
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