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Building Products January 2018

DAMP-PROOFING, SEALANTS AND ADHESIVES JANUARY 2018 | BUILDING PRODUCTS 53 These days, the most effective masonry water repellents are based on silicones. The main reasons for this are that modern silicone waterrepellents form an incredibly long and lasting bond with most types of masonry, and that they line the pores of masonry rather than blocking them – allowing the masonry to ‘breathe’. The first silicone water-repellents were simple solutions of silicone resins in carrier solvents such as white spirit. Once applied, these formed a resin coating on the masonry surface and suffered from the same drawbacks as other resin solutions such as linseed oil based products – i.e. they blocked the pores of the masonry and trapped moisture. The 1970s saw the introduction of waterrepellents based on specialised silicones. These were still solvent based, but the molecules were smaller than silicone resin molecules, allowing them to penetrate below the surface of the masonry. Their water-repellent effect was partially derived from lining the pores of the masonry, rather than blocking them, which meant that treated masonry retained a degree of breathability. Further developments in the 1980s saw the introduction of another class of silicones, known as alkoxy silanes. These had an even smaller molecular size which allowed deeper penetration into masonry and improved breathability. These developments meant that by the mid- 1980s, solvent based silane/siloxane water-repellents were available that combined excellent water-repellency with high levels of breathability (<10% reduction in water vapour permeability). The best products had long lifespans (often more than 10 years) compared with cheaper products based on metal stearates, which were typically broken down the effects of UV radiation from the sun within two to four years. However, penetration depths were limited to a few millimetres, which limited their performance as even the smallest surface crack could allow winddriven rain to pass behind the treated layer. In terms of performance, the solvent based silane/siloxane water-repellents were not improved upon until the introduction of masonry water-repellent creams in the 2000s. These also utilised silanes and siloxanes as their active ingredients, but formulated into a high-build cream that allowed deeper penetration into the masonry (>10mm in Fletton bricks for the best formulations). Masonry water-repellent creams appear white when applied to masonry, but become colourless once the cream has penetrated. The proportion of active ingredients as well as the blend of silanes and siloxanes varies considerably between different cream formulations, so it is difficult to make generalisations. However, the high penetration depth of good quality masonry water-repellent creams provides longer life expectancy – largely since any molecules of active ingredient more than 2mm beneath the surface of the masonry cannot be attacked by ultraviolet light. A further benefit of cream formulations is that they are much easier to apply around details such as doors and windows than liquid products which tend to be applied by spray. The durability of silicone water-repellents is largely due to the strong covalent bond that they form with the silicon atoms present in most masonry materials including brick, mortar, and sandstone. However, certain masonry materials such as pure limestones do not contain these silicon atoms and consequently the performance of silicone based water repellents is reduced on these substrates. These substrates can be treated through specialist techniques and product selection, but it is advisable to seek technical advice from the product manufacturer before doing so. www.safeguardeurope.com A new CPD seminar created by Safeguard Europe offers an in-the-workplace CPD called Dealing with Penetrating Damp which sets out four steps to help architects, builders and other building professionals to deal with both the causes of penetrating damp and the factors which can exacerbate the problem. For booking information call 01403 210204 or email info@safeguardeurope.com. The most effective masonry water repellents are based on silicones


Building Products January 2018
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