Delegates to the AMI conference, Waterproof Membranes 2007, appreciated the range of discussion topics, covering all types of membrane material from polymer modified bitumen to the latest thermoplastic elastomers. There was a degree of surprise at the rate of technical innovation in such a well established industry. There was a lot of discussion about the rate of penetration of polyolefins and the potential for further market innovation and growth following the introduction of several new polyolefinic resin families.
John Nash (AMI Consultant) in his presentation on market dynamics said ‘this is a segment in which excellent returns are available to well organized companies’. 750,000 tonnes of polymer is used in membranes in Europe, from flat roofing to landfill. Around 50% of this is polyethylene, 30% polypropylene, 15% PVC and 5% EPDM/butyl. In the EU modified bitumen still accounts for 75% of the market. In the US this figure is very different with bitumen taking around 35% and rubber materials around 30%.
A typical waterproofing membrane structure comprises a top layer of 0.5-1.5 mm, a reinforcement fabric and a bottom layer of 0.5-1.5 mm with an underlying fleece protective layer. Krauss Maffei Berstorff supplies production technology. EPDM involves rubber extrusion and calendering, lamination of reinforcement, curing and fleece application. PVC membranes can be made by melting the PVC, calendaring, lamination of reinforcement and fleece lamination. PVC and TPO membranes can be made by sheet extrusion, calendaring and lamination of reinforcement followed by fleece. Coatema supplies the technology for textile coating in membrane production. These products have been used in places such as the Millennium Dome in London (glass fibre fabric with PTFE coat), the Esplanade in New York (PVC coated PET fibre) and the Daimler Chrysler design centre in Sindelfingen (ETFE weave with THV coat).
Heromelt Adhesives design and manufacture “peel and stick” membranes, with the advantage of full adherence and broader stress distribution. It also lowers VOCs and is relatively quick to apply. The latest membrane is produced from TPO. Valeron has also developed peel and stick technology for its cross-laminated films, used as reinforcement in membranes, for example as a surface protection layer on bitumen. Applications include the breakwater wall and the Burj Al Arab hotel in Dubai. Basell Polyolefins is a supplier of TPOs for use in single-ply roofing: the material offers hot air weldability, colourability and heat resistance together with bitumen compatibility. The US is a strong driver in this field with 28% market share of TPOs estimated for 2007.
Bitumen membranes have been in use since the ancient Mesopotamians. In 1965 Italy brought in APP modification followed by SBS in 1974. Current developments include the super membranes and white/coloured products. Alphamin produce polymers for modifying bitumen and has been pushing the industry forward with improved properties.
With membranes in use as pool liners and bases for gardens in green roofs, waterproof properties are critical. AB Mess-Und Trocknungstechnik applies an electrical current to the wet membrane to detect leakage points. Common causes of problems are damage due to the use of roofs for storage, pedestrian traffic and problems in installation.
Jim Hooker of the Single Ply Roofing Association has looked at membrane durability. UK clients are demanding longer guarantees of performance. Lifetime is affected by installation, abuse and maintenance as well as core materials. Local stress concentration such as at an internal angle should be avoided. Drainage planning is very important – in one study at Napier University the repair frequency was reduced 40% in areas of good drainage. Increased product thickness may be needed to extend lifespan (e.g. 15 years – 1.5 mm, 20 years – 1.8 mm).
Trelleborg Building Systems is involved in EPDM rubber membrane production. In a recent project membranes were used to divert the Kolubara River in Serbia. Neshvyl fabricated and installed the membranes. The panels were planned in advance and overlapped by 100 mm with seams welded using thermal fusion dual track hot wedge.
Lanxess supplies EPDM and EVM into this market. By modifying the material with coatings and using whiter compounds, the surface temperature of an EPDM roof can be lowered from 90 C to 45 C. EVM has better UV resistance, can be produced transparent and has good fire resistance.
The European Construction Products Directive has implications for the membrane industry. Lucobit has looked at the external fire performance of roofing membranes using test methods according to EN 1187 and classification according to EN 13501-5.
Plasticisers are critical to membrane lifespan. BASF is a supplier and recommends a polymeric plasticiser for PVC exposed to bitumen or chemicals, and a monomeric plasticizer in other circumstances, such as phthalates or adipates. Ciba Specialty Chemicals provides heat and light stabilizers for membranes, for example high molecular weight HALS for polyolefins Tinuvin for PVC. Other additives are used to inhibit microbe and fungus growth.
Roof coatings have been around for thousands of years from beeswax in 3000 BC to coal tar in the 1700s. The US EPA has noted that white roof coatings (radiation control coatings) are a simple way to improve building energy efficiency. Reflecting the light reduces interior temperature and slows ageing. United Coatings supplies white coating systems that can be applied to existing roofs.
The Fraunhofer Institute for Building Physics has studied the use of vapour permeable membranes for moisture control in flat roofs from Helsinki to Dubai. The surface colour of membranes is a big factor – bright colours reduce the drying potential in summer. DSM Engineering Plastics has a new TPE-E tested for use in breathable membranes. In molecular terms the hard block is formed from PBT and the nature of the soft block determines elasticity and breathability. A special UV-resistant masterbatch has been developed for roofing.
Dow Europe has TPO for membranes. The product has been used in roofing and civil engineering applications such as tunnels.
The Swedish Royal Institute of Technology has an extensive roofing research division and has examined joint integrity. The join adhesion should be as strong as the internal membrane cohesion.
The botanists also study membranes. A plant and soil layer protects a membrane from UV exposure and wind lift. However, high bio-mechanical force is applied by some rhizomes and roots. A growing root will enter a weak point and can burst the joints as it grows. Roots can also overstretch membranes. Rhizomes have a hard spiky end and act on membranes like a chisel. The Weihenstephan University has developed test methods for plant penetration of different membrane materials. Root damage can be stopped by using a retardant in the membrane. Rhizomes have to be stopped by a hard carrier.
A wide range of issues was covered at Waterproof Membranes 2007 – speakers are now being sought for the next event from 3-5 November 2008 in Cologne.