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RCI May 2017

LRWA VIEWPOINT Which liquid to use? The science explained Part 2 Last month, Terry Wain, technical secretary at the Liquid Roofing and Waterproofing Association (LRWA), explained some lesser known chemistry types of cold-applied liquid waterproofing. In this article, he offers specification and application advice on more technologies within the liquid chemistry family In the April edition of RCI, the LRWA provided an overview of three of the lesser known liquid chemistries – polyurea, cold applied liquid bitumen and thermoplastic block copolymers (SEBS) – describing the qualities of each technology. This month, we’ll further explore why there isn’t one liquid applied membrane suitable for every project, explaining the differences between other liquid technologies including PMMA (Polymethyl Methacrylate), Polyurethane, GRP (Glass Reinforced Plastic) and Flexible Polyester. PMMA (Polymethyl Methacrylate) PMMA was first developed in 1928 by chemists William Chalmers, Otto Röhm and Walter Bauer, and was brought to market in 1933 by the Rohm and Haas Company. Now widely used in the construction industry, the success of PMMA relies on its rapid curing qualities as it can dry in 30-40 minutes and in some cases even quicker if required, by using additional catalyst. PMMA-based systems tend to have a minimum of two components, the first being the resin and the second being a catalyst or activator. Contractors will mix the components together on site, starting a chemical reaction creating heat which cures the product. The solvent-free, cold-applied liquid resin cures rapidly even at temperatures around 0°C or lower, and is installed wet-on-wet. This means the polyester reinforcing fleece is first saturated with liquid resin, bonding the membrane to the substrate, with the surface layer then applied onto the bonding coat whilst still wet – therefore forming a single, seamless membrane of uniform thickness. PMMA is durable, flexible, hard wearing and ideal for waterproofing projects whereby access to site is very limited and work must be completed extremely quickly. This includes communal walkways, stairways, car parks or balconies on occupied housing blocks where having the building empty or restricting access to homes for long periods of time is just not an option. On smaller roof areas, a one-day application may be possible as there is no need to wait for drying between coats. 064 MAY 2017 RCIMAG.COM Polyurethane Polyurethane systems are probably the most popular chemistry types with a long track record in the UK market, because they are seen as versatile materials that can be used in a multitude of applications. Established for more than 30 years, Polyurethanes can provide a cost-effective option for metal roofs, gutters, flat roofs of any size, warm roofs, green roofs as well as trafficked walkways, balconies and terraces – further cementing their versatile benefits. Products are available as both single and twin pack, may use glass fibre matting or polyester fleece reinforcement, single (wet-on-wet) application or multi-layer applications; and can be reactive systems, moisture triggered or moisture cured. There are a wide variety of Polyurethane products on the market, some have an odour and some are odour free; making them ideal for use in sensitive areas such as nurseries, hospitals, schools, causing little disruption to occupiers of the building. The elastomeric nature of Polyurethane coatings allows high flexibility to mitigate movement in the underlying structure, reducing the occurrence of potential cracks. As with many liquid waterproofing systems, Polyurethanes also give inherently good chemical resistance and excellent durability against long-term UV radiation, heat and water ponding. Glass Reinforced Plastic This technology is often referred to as GRP, glass fibre or fibreglass, and consists of a glass fibre reinforced polyester resin. It was first developed around the 1940s and thanks to its non-corrosive, high strength and excellent waterproofing properties, GRP was quickly adopted by the roofing industry from the 1950s. GRP systems are predominantly used for Terry Wain is technical secretary for the Liquid Roofing and Waterproofing Association (LRWA). The LRWA consists of the leading manufacturers of liquid applied waterproofing, approved contractors and related materials suppliers Above: Polyurethane has been established for more than 30 years and its versatile qualities means it can be used on almost any surface Right: GRP was first developed around the 1940s and is predominantly used for domestic properties with small flat roofs


RCI May 2017
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