Sealed Units & Sealants 44 December 2013 Compatibility matters Phil Turley, glass products business manager at Kommerling UK, explains the importance of compatibility with regards to materials in the glazing industry. In order to understand the increasing importance of compatibility in the glazing and wider construction market, the first thing to be established is a definition of compatibility. Substances or compounds may be deemed compatible if they do not react chemically or physically in such a way as to compromise the intended use of the product or affect the merchantability of the assembly, in this instance the window, of which they form part. Alternatively, according to DIN 52460, substances are defined as compatible if no ‘harmful interaction appears between them’. Harmful interactions are all interactions between substances which affect the function or the durability of a system. In the context of a new building, a harmful interaction may compromise the inherent strength of a glass unit, resulting in a loss of the overall strength, stability or life of the building. In the most extreme case, this could also jeopardise its occupants. As architects continue to stretch the boundaries for building shape and form, construction, building techniques and materials are constantly stretched to recreate the futuristic shapes and forms they demand. With this comes a need for greater consideration and an improved level of understanding of this small but critical element, the sealants. It is no good having a building where the walls and roof are designed to last 50 years but the seals will only be viable for 20 years. The visual impact of these 21st century edifices is greatly enhanced by the clever use of glass. Using insulated glass in such an innovative way brings with it its own problems for the installer, not least of which is the vast range of materials which are likely to come into contact with the edge seal. Glazing silicones, weather sealants, PVC, wood, varnishes, rubber profiles, adhesive tapes, PVB foils, glazing blocks and coatings on glass, may all be used singly or in a number of combinations around the edge seal. This can result in the direct or indirect contact of the different elements which may induce harmful interactions that then affect the function of the complete glazing system and its durability. The key to this problem is understanding the importance of compatibility between the elements involved. What happens when incompatibility occurs? Incompatibility may manifest itself in a number of different ways: • Incompatibility between primary and secondary sealant. Softener migrates from the secondary sealing through the primary sealant into the inner space of the IG unit. • The wrong fixing of glazing blocks. Silicone used to fix a setting block may come into direct contact with the secondary sealant and the laminated glass. This may have a detrimental effect on both the edge seal and the PVB foil. One way to avoid this is to fix the setting block with a compatible silicone to the sash. • Stepped IG unit with an incompatible silicone at the top in combination with a sealant depth which is too high. When this occurs the extender from the silicone migrates through the secondary sealant and washes out the primary sealant, resulting in a loss of functionality. • Incompatibility between weather sealant and secondary sealant. No backer rod and too much sealant applied (seal depth). How can these problems be prevented? These problems do not happen overnight and insulating glass producers and the window or facade builder play a significant role in their alleviation. There are a number of checks that should be incorporated prior to and during construction. The IG producer should: • Check compatibility of primary and secondary sealant. • Check compatibility with laminated glass. • Check compatibility with glass coatings. • Follow the application instructions, both in terms of preparation and climactic considerations. • Ensure correct storage and transport. The window and/or facade builder should check the following: • Compatibility with glazing materials. • Compatibility with setting blocks. • Compatibility with backer material. • Compatibility with other materials in contact. • Follow the application and glazing instructions. In addition, there are other guidelines which may help reduce the risk of incompatibility: • Use only well known systems, ideally from one supplier who has a product range that encompasses both glazing, silicone and weather sealant. • If possible, test glazing blocks before using or use ‘inert’ plastics like PP or PE. • Ensure compatibility of glazing blocks with adhesive or use ‘hook blocks’ as a constructive alternative for fixing to the frame (ensure aerating and moisture pressure regulation). • Backer material. Ensure closed cell PE-cords (sealing depth). The challenge of sealant compatibility combined with sealant performance is one that will not go away, in fact it will become more prominent as architectural, environmental and commercial demands become even more demanding. Recognising this need, sealant manufacturers continue to invest in research and development and installers and fabricators also have an obligation to understand that compatibility matters now more than ever before.
GGP December 2013
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