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Westerland slate
Westerland slates are manufactured using portland cement together with a non-asbestos formulation of superior blended synthetic and cellulose fibres. Westerland slates are pigmented during production and are fully compressed. They are finished with a high quality acrylic coating to both faces and all edges. Westerland slates are suitable for all types of projects and are an ideal, economic alternative to natural slates. Westerland slate is available in Blue/Black and Welsh Blue finishes. Fibre cement slates are lightweight, easy to cut and fix. Quality Assurance
Colours Westerland slate is available in Blue/Black and Welsh Blue. Performance Compatibility Westerland slates are compatible with most common building materials, except those vulnerable to alkaline attack. When materials such as aluminium are used as flashings or gutters they should be protected and maintained with bituminous paint where they are subject to water run-off from the slates. Tolerances Westerland slates are made to the following dimensional tolerances in accordance with BS EN 492: 1994. Length or width: ± 3.0 mm Westerland slates exceed the requirements of Class B (the highest) of BS EN 492 giving an average bending moment greater than 50 Nn/m. Density Westerland slates have a minimum density of 1700 kg/m3 when tested to BS 4625: Section 14 and to BS EN 492 section 7.3.1. Fire Westerland slates achieve the following ratings: BS 476: Part 2: 1989 and BS 476: Part 7: 1987. Fire Propagation Index (I) of 0.9, a Sub index (ii) of 0.3 and a Class 1 surface. Class O surface as defined in the various national Building Regulations. BS 476: Part 3 1958 EXT. SAA BS 476: Part 3 1975 Class P60 Frost Westerland slates show satisfactory frost resistance after 100 freeze/ thaw cycles when tested to BS 4625: Section 14 and satisfy the requirements of BS EN 492 section 7.4.1. Thermal The coefficient of linear expansion of Westerland slates is approximately 8 ´ 10-6 mm/°C. This is equivalent to an expansion of 0.08 mm/m for a 10°C temperature change.Thermal conductivity: (k value) is 0.35W/m°C. Effects of chemicals During tests Westerland slates have been found to have a good resistance to chemical attack, however it should be noted that prolonged exposure will cause surface degradation. In areas where this may be excessive please consult Cembrit for further advice. Biological Westerland slates are vermin and rot proof. The acrylic coating of the slates will reduce the potential growth of moss and lichen. General design considerations Westerland slates laid to BS 5534 will meet the strength requirements for the imposed and uniformly distributed wind and snow loads etc. The site exposure rating and the pitch of roof rafters will determine the size, pattern, lap and fixings for the slates. For UK and Northern Ireland locations, BS 5534: Part 1: 1997 will indicate the expected degree of exposure. Wind driven rain ratings less than 56.5 l/m2 per spell are described as ‘moderate’ (see table 1) and those above 56.5 l/m2 per spell are described as ‘severe’ (see table 2). Detailed guidance on wind load calculations is given in BS 5534: Part 1 and in BS 6399: Part 2: 1995 and Part 3: 1998. In locations where abnormal conditions may be anticipated such as elevated sites, coastal locations areas of heavy snowfall etc., the recommendation for ‘severe’ should be followed. Additional information can also be found in BS 8104. Table 1 Moderate exposureless than 56.5 l/m2 per spell
Table 2 Severe exposuregreater than or equal to 56.5 l/m2 per spell
Table 3 Technical specification
Identification A minimum of 25% of the slates are marked on the underside using the following format: BB104200NTB2 Where the first character denotes the factory of origin; the second character the Strength Classification from EN 492 section 7.3.2; the next six numbers denote the shift and year of manufacture; NT denotes non-asbestos technology; and the final two characters show the production line and painting line used for manufacture. Supply All Cembrit ’s products are supplied directly to approved accounts, roofing contractors and builders’ merchants. Westerland slates are delivered on wooden pallets, either banded or fully encased in cardboard and shrink wrapped. Prices are available on request from Cembrit Ltd. Sitework Storage Westerland slates should not be allowed to become wet during storage as this may cause efflorescence staining as a result of water accumulating between the slates surfaces. If stored outside for short periods, the polythene hood should be removed and the slates open stacked and covered with a tarpaulin. Working Westerland slate can be cut using the traditional method of scribing and breaking over a straight edge. Angle grinders are not recommended due to nuisance dust levels. Additional fixing holes should be drilled using a 4.5mm drill bit. Holes should not be less than 20 mm from the edge of the slate. After cutting or drilling remove all dust from the slate to avoid possible staining. Fixing Slates must be laid in accordance with the Code of Practice for Slating and Tiling, BS 5534: Part 1 :1997 Design, and the Code of Practice for Workmanship on Building Sites – Slating and Tiling, BS 8000: Part 6: 1990. The method of fixing is to centre nail each slate with two 2.65 mm ´ 30 mm long copper nails and secure the tail of the slate with a copper disk rivet.Further details are available in our fixing guide. Battens Minimum batten sizes as recommended in BS 5534: Part 1: 1997 for pitched roofs and vertical cladding:
To avoid splitting the batten, the maximum nail diameter should not exceed one tenth of the batten width. The roof should always be set out so that the long edges of the slates are parallel to the direction at which the water will run off the roof. In some instances this may result in raking all the eaves and the ridge. The ends of any batten should be fully supported and the length of any batten should not be less than 1.2 m (except where this is unavoidable) and nailed to a maximum of 600 mm centres. Where the roof is close-boarded, counter battens should be used down the slope in the roof on the line of the rafters. Counter battens should be at least 38 mm wide ´ 12 mm deep and, where impermeable underlay is specified, of sufficient thickness to provide ventilation between the boarding and underlay.Underlay Suitable underlay should have a minimum standard to BS 747:1977 Type 1F and/or should have a British Board of Agrément Certificate. The underlay should be draped over the rafters, or fully supported on boarding or sheathing, should allow any moisture to drain and should extend over the tilting fillet, fascia board and into the eaves gutter. Lead staining risk Lead develops a lead carbonate patina which, if washed over slates by rain or other moisture, causes unsightly staining. To prevent this reaction marring the work, it is advisable to treat all lead including soakers and flashings, with patination oil before any rain occurs, and not later than the day the lead is fixed. Patination oil, a low viscosity fluid intended for this purpose, should be applied evenly. It is readily available from builders merchants. Technical services For assistance with all aspects of the specification and application of any of our products, please contact Cembrit Head Office. Typical specification Roof to be covered with Westerland slates, size ....... mm ´ ....... mm, laid to a minimum head lap of ....... mm.
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Westerland slate has an appearance very close to that of natural slate. Its attractive riven surface and natural dressed edge make it an ideal solution for situations where presentation is important. 
Westerland slates are manufactured in accordance with a quality assurance system to ISO 9001 and to the requirements of BS EN 492 product specification for fibre cement slates and their fittings.
Cembrit Limited, 57 Kellner Road, London SE28 0AX Tel: 0208 301 8900 Fax: 0208 301 8901 sales@cembrit.co.uk |