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Building Products October 2017

DAMP PROOFING, ADHESIVES AND SEALANTS MAKING SENSE OF SEALANTS Sealants are a large and ever-evolving product category. As a result, choosing the right sealant for the right job isn’t always easy. To help make sense of the different options available, Building Products catches up with Jake Griffin. 70 BUILDING PRODUCTS | OCTOBER 2017 occurring which interferes with the silicone’s adhesive properties. Likewise, acetoxy cure silicones are unsuitable for use with natural stone because the acetic acid they gave off can react with the stone. Neutral cure silicones on the other hand generally adhere well to all the materials that acetoxy sealants are unsuitable for. As their name suggests, they remain pH neutral during curing and give off no acetic acid. This enables them to be used with plastics, metal and cement with none of the reactions and resultant issues that occur from using acetoxy cure products. Neutral cure silicones have two main sub groups, oxime and alcoxy. Like acetoxy sealants their names reflect the smell that they give off as they cure. Oxime sealants have a rather pungent odour of oxime and alcoxy sealants have the sweet smell of alcohol. Neutral cure oxime sealants can offer very good adhesion to pvc-u and have become a cost effective choice for perimeter sealing in the glazing industry. Neutral cure alcoxy silicones also offer When it comes to sealants, today’s building industry professional is not short of choice. There are numerous products out there from an equally wide array of manufacturers. All of these products are marketed in different ways and for different applications. It is perhaps this plethora of choice that has led to a situation where, for many, it can be difficult to ‘see the wood for the trees’. Thankfully though cutting through the confusion is not difficult – the key to understanding which sealant is best suited to your intended project or use ultimately comes down to understanding the different types of base material that sealants employ. It is these ‘raw ingredients’ that determine the key characteristics of a product – such as its quality, ‘toolability’, drying time, flexibility/movement capability and adhesive properties. The base material used by all sealants broadly falls into one of four main categories; namely silicone, polyurethane, water-based (commonly referred to as acrylics) and hybrid polymers. Taking each material in turn, silicone sealants can be further split into sub-groups with acetoxy cure and neutral cure being the two most frequently encountered. These one-part silicone sealants cure using the moisture that is present in the air surrounding them. Acetoxy cure silicones tend to be the most widely used - quite possibly because they are both cheap and versatile. They smell, often quite pungently, of vinegar and can be used without issue in many applications and in conjunction with many materials. However they do produce acetic acid during curing which makes them unsuitable for use with certain substrates. This includes untreated/unprimed metals like lead, copper, brass and steel because the acetic acid can oxidise the metal’s surface leading to poor adhesion. Similarly, acetoxy cure silicones are not suited for use with any material containing cement such as concrete, plaster, mortar and render. Cement is alkaline and as an acetoxy silicone becomes acidic during curing there is a risk of a reaction


Building Products October 2017
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