MMA Yearbook 2007 45 y-made cements Cement type Standard notation Portland cement – CEM I CEM II cements Portland-limestone cement CEM II/A-L and II/A-LL Portland-fly ash cement CEM II/A-V CEM II/B-V Masonry cements Inorganic filler other than lime MC 12,5 Lime as filler NOTE. The letters ‘A’ and ‘B’ in standard notations for CEM II cements indicate the proportion of secondary constituent in the cement. ‘A’ indicates from 6% up to 20% by mass, whereas ‘B’ indicates from 21% to 35% by mass. Table 1: Factory-made cements (generally available) for use in masonry mortars Mortar strength classes Equivalent mix proportions BS 5628-3 mortar CEM I cement ‘Non-CEM I’ cements Mortars: designed to BS EN 998-2 or prescribed to NA.1 of BS EN 998-2 or prescribed to draft NA of BS EN 1996-1-1 or prescribed to NBS sections Z21 and F10 CEM I : Lime : Sand (with / without airentrainment) CEM I : Sand (with / without airentrainment) CEM II : Lime : Sand (with / without airentrainment) CEM II : Sand (with / without airentrainment) Masonry cement*: Sand Masonry cement† : Sand M 10/M 12 1: ¼ : 3 Not suitable 1: ¼ : 3 Not suitable Not suitable Not suitable (i) M 5/M 6 1 : ½ : 4 to 4½ 1 : 3 to 4 1 : ½ : 4 to 4½ 1 : 3 to 4 1 : 2½ to 3½ 1 : to 3 (ii) M 2,5/M 4 1 : 1 : 5 to 6 1 : 5 to 6 1 : 1 : 5 to 6 1 : 5 to 6 1 : 4 to 5 1 : 3½ to 4 (iii) M 1/M 2 1 : 2 : 8 to 9 1 : 7 to 8 1 : 2 : 8 to 9 1 : 7 to 8 1 : 5½ to 6½ 1 : to 4½ (iv) *Masonry cement incorporating an inorganic filler other than lime / †Masonry cement incorporating lime as the filler. NOTE 1. One-to-one equivalence between CEM I and CEM II cements has been established for strength classes 32,5 and higher. NOTE 2. Where cements incorporate an air-entraining/plasticising additive the addition of air-entraining admixtures on site is usually unnecessary (except with poor sands) and may impair strength and durability. NOTE 3. A designation (iii) mortar is equivalent to the ‘general purpose mortar’ described in BRE Digest 362 [6]. Table 2: Equivalent masonry mortar mixes using factory-made CEM I, CEM II and masonry cements Title Publisher Date Guide to materials for masonry mortar British Cement Association 2005 Specifying CEM II cements for use in masonry mortars British Cement Association Expected autumn 2006 Factory-produced ready to-use mortar for masonry Mortar Industries Association 2005 Factory-produced silo mortar for masonry Mortar Industries Association 2005 Factory-produced lime : sand mortar for masonry Mortar Industries Association 2005 Mortar for masonry, guidance on specification, types production and use Concrete Society 2005 Mortars – section Z21 in the National Building Specification National Building Specification Revision expected autumn 2006 Brick/block walling – section F10 in the National Building Specification National Building Specification Revision expected autumn 2006 PD 6678, guide to the specification of masonry mortar British Standards Institution 2005 Table 3: Guidance on use of factory-made cements (and other materials) in masonry mortars condition(s) is the ‘key’ to specifying durable masonry mortar. Equivalence of different cements for the same mortar designation has been established in major specifications and it should, therefore, only be necessary to specify a cement type (or source of supply) by consideration of: sustainability credentials; fresh wet and hardened properties of the cement within the mix of mortar materials/composition selected; sulfate-resistance, where needed; consistency of colour; availability of supply. Other characteristics will rarely be relevant. References [1] British Standards Institution. BS EN 197–1, Cement – Part 1: Composition, specifications and conformity criteria for common cements. [2] British Standards Institution. BS EN 413- 1 Masonry cement – Part 1: Composition, specification and conformity criteria. [3] British Standards Institution. BS 4027 Specification for sulfate-resisting Portland cement. [4] British Standards Institution. BS 5628- 3 Code of practice for use of masonry – Part 3: Materials and components, design and workmanship. [5] British Standards Institution. Draft National Annex to BS EN 1996-1-1. Eurocode 6: Design of masonry structures – Part 1-1: General rules for reinforced and unreinforced masonry structures. [6] Building Research Establishment. Digest 362 Building mortar. [7] British Standards Institution. BS EN 998-2 Specification for mortar for masonry - Part 2: Masonry mortar. . Reader enquires to: info@bca.org.uk

46 MMA Yearbook 2007 Cast stone can add to the design quality and kerb appeal of modern masonry construction. Andy Cotton, Chairman of the UK Cast Stone Association, explains why. Elegant elevations Everybody’s idea of what constitutes a well-designed façade is different. In the case of modern masonry construction, high performance capabilities and long-term sustainability come as standard, so the real divide is often between aesthetic factors. Cast stone is a firm favourite for transforming plain façades into something special. There’s a simple reason why. This special form of simulated stone offers class at an affordable price. It can stand alongside carved natural stone in appearance and performance, but normally costs significantly less. It’s a familiar and much-used alternative to natural stone and has caught the imagination of architects, from the classical past in Britain, to modern day masters. Cast stone evokes a sense of timelessness that fits in with any form of masonry construction, from domestic housing, to cathedrals. It’s a highly versatile material, suitable for period and contemporary styles, stone and reconstructed stone buildings, and it complements brickwork and render. Attention to detail The material is ideal for any architectural purpose that calls for fine detail around entrances, openings and gables. Made offsite, it’s highly versatile and regularly used for new build, extension and refurbishment projects, including areas of sensitive planning constraints or where stone is a predominant material. All types of architectural stonework can be produced – large, small and structurally reinforced – and cast stone’s ability to form complex shapes makes it ideal for ornate detailing. Since at least the eighteenth century, cast stone has been used for mouldings, columns and their entablatures, cornices, balustrading and keystones. In housing, cast stone details such as porticos, window heads and cills, string courses and quoins are a tried-and-tested solution. Cast stone can also take the form of ashlar masonry. Cast stone ashlar blocks are simple and economical to use, performing and weathering in much the same way as natural stone. These smooth square or rectangular blocks can be moulded to a natural stone finish if required. Laid in horizontal joints, cast stone ashlar blocks permit very thin mortar joints, adding to the classical fine quality appearance and strength of the elevation. Reconstructed stone So what is cast stone? It’s a high-quality facing material synonymous with reconstructed stone. As an industry we say it is ‘any material made with natural aggregates and cementitious binder that is intended to resemble and be used in a similar way to natural stone’. Despite its composition, it would be a mistake to think that cast stone has much to do with mass concrete. Often, its colour is the result of choosing a sandstone or limestone aggregate with the appropriate inherent colour. So the final product can echo the way natural stones are themselves coloured. Although critics of cast stone have argued that it never weathers like natural stone, the fact is that it can and does. Cast stone not only satisfies the ‘truth to construction’ architectural argument, but it can beat natural stone on strength, moisture penetration, colour and textural consistency. More readily available than worked natural stone, it’s free from imperfections, and it looks much the same. The details come ready-made or bespoke, tailored exactly to a specification. Versatile material For an example of just how versatile cast stone can be in matching the local architectural style, you’d be hard pushed to better a recent development in the historic city of Bath. New homes were constructed in a neo-classical style using cast stone ashlar walling, with matching cast stone details including porticos, string courses and window cills. The combination of fine cast stone, classical detailing and quality construction resulted in façades that are virtually indistinguishable from their Georgian counterparts. The cast stone was supplied by Bradstone to Magenta Properties. “By offering a cost-effective means of replicating traditional designs, towns such as Bath are able to retain their historic character, despite on-going expansion and modernisation,” said Bradstone’s Mark Barter. In order to assess the public preference for cast stone and quantify the value of that preference to developers, the UKCSA commissioned a survey from Ipsos MORI earlier this year. The survey showed a nationally representative sample of more than 2,000 people two photos of the same