Feature Pre-cured Silicone Sealant in Metal Building Applications By Jason Bakus re-cured joint sealant is produced by extruding an elastomeric material and allowing it to cure to a flexible product in a controlled manufacturing environment. As its name suggests, the product is 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. With the outer edges adhered, the middle of the pre-cured sealant—which is not bonded—acts as the area for expansion and contraction. The product is manufactured in widths ranging from less than 25 mm (1 in.) to wider than 305 mm (12 in.). Several types of pre-cured sealant have been used in the industry over the years, ranging from polyurethane and polysulfide to silicone. Each kind offers unique chemical and physical characteristics. Silicone pre-cured sealant, however, has been the most commonly used type in construction applications for several reasons. Due to its molecular structure and high bond energy, silicone has excellent aging characteristics and is resistant to ultraviolet (UV) light and weathering. The result is a longer effective lifespan than organic products such as ethylene propylene diene monomer P (EPDM), polyurethane, polysulfide, and butyl, which are prone to this sort of damage. As silicone does not degrade when exposed to the elements, it is possible to produce very thin material (i.e. 1 to 2 mm [0.04 to 0.08 in.]), minimizing expansion and contraction forces on the substrate. The movement capability for silicone pre-cured joint sealant can be as much as +200 or −75 per cent, which is significantly more than other products used in similar applications. Coupled with the thinness, this high movement capability allows the material to easily handle the multi-directional movement commonly found in metal building applications. Additional advantages include a wide operational and installation temperature range (including the extreme hot and cold conditions found in various parts of North America), and better resistance to colour fading due to inorganic pigments typically used in silicone formulations. Pre-cured silicone sealant has been used for quite awhile in a variety of building envelope restoration applications. Over the last several years, these products have begun to be used by manufacturers and erectors within the metal building industry. 54 January 2010 Construction Canada CC_JanFeb10.indd 54 12/22/09 11:56:29 AM All images courtesy Sealex