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Building Products October 2017

DAMP PROOFING, ADHESIVES AND SEALANTS OCTOBER 2017 | BUILDING PRODUCTS 71 excellent adhesion to an enormous variety of materials, including pvc-u, and can be used for a wide range of applications – from glazing and engineering to general construction. These sealants tend to be slightly slower curing and offer extended tooling time. The 100% neutral cure products tend to be used for ‘bedding in’ double glazed units into wooden frames. This is because being neutral cure they do not release any chemicals that could degrade the insulating glass seals. It is also important to point out that no silicone sealant is suitable for use with bitumen, asphalt or tar products. Nor are they over-paintable. Turning to water-based sealants (or acrylics) these sealants owe their name to the fact that they are based on fillers and other materials bound together by a water-based polymer emulsion. These sealants cure by evaporation. Depending on the polymer used, water-based sealants offer varying degrees of water resistance and flexibility to suit the particular application where they are to be used. Once dry, they are also over-paintable unlike their silicone sealant counterparts. They also tend to be easier to use than silicones and any excess material can be easily removed with a damp cloth. All water-based sealants have an element of ‘flexibility’ but in general tend to be less flexible (have lower movement capability) than a silicone sealant. They also take longer to become water resistant than silicone sealants and their speed of drying varies substantially based on atmospheric conditions. The quickest drying times can be achieved in warm, dry and well ventilated conditions. Overall, silicone sealants will outperform water-based products in most departments when used as sealants. Focusing next on polyurethane (or PU) sealants, these products offer excellent adhesion to most materials and can be tailored to specific needs with great flexibility. The harder grades have good abrasion resistance which makes then suitable for use in concrete expansion joints. They are also over-paintable. By and large, PU sealants are not employed in domestic environments. Instead they are widely employed in engineering, automotive, marine and commercial construction applications. Finally, there are hybrid sealants – which arguably represent the next stage in sealant evolution and are growing exponentially in popularity. Also known as MS sealants, hybrids employ hybrid polymers - a combination of polyurethane or polyether with silicone type curing mechanisms. This advanced technology enables hybrids to offer the best of both worlds, combining many of the benefits of both silicone and PU sealants. Hybrid sealants are the most versatile available and offer good adhesion to a vast array of materials including metal, plastic, glass, wood and ceramic. This makes them an effective ‘all-in-one’ product which can be used for a wide range of applications including construction, engineering, glazing, marine and automotive uses. They can also be applied in damp conditions, even underwater. Hybrids do have a degree of paintability but it is always worth checking with your particular type of paint. Although the technology is now several years old, hybrids were not very common until quite recently, perhaps because they tend to be more expensive than the other sealant types. Their market acceptance is growing and – with this growth – manufacturers are widening their product offering to allow hybrids to compete likefor like with silicone sealants. Silicone polymer is currently in short supply globally and prices are on the rise, so the price differential between hybrid systems and silicone sealants is narrowing. So perhaps this is the time for hybrid sealants to become a major part of the UK sealant market. Jake Griffin is a chemist at Bond It


Building Products October 2017
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