BRICKS, BLOCKS & PAVERS NATURAL SELECTION Hard landscaping is becoming increasingly important as the public, commercial and private sectors face the challenges of urbanisation. Here Malcolm Gough shares his top tips when specifying natural stone paving. More than half of the world’s population now lives in cities and this figure is set to increase to 70% by 2050. Urbanisation comes with a number of challenges including efficient planning of outdoor spaces. Increasingly, hardwearing materials are becoming more important because of higher levels of pedestrian traffic and equally, aesthetics must be considered as people look to differentiate and create distinct spaces. Natural stone is an ideal material as it is extremely durable and no two stones are the same, however to help architects and specifiers make a more informed choice, here is a list of a few important things they should consider. The first thing in natural stone’s favour is its durability. Unlike concrete landscaping alternatives, which are made from composite aggregate mixes that become exposed after a few years of traffic (allowing moisture to penetrate the surface), natural stone will keep its integrity for many years. However, there are 44 BUILDING PRODUCTS | OCTOBER 2016 a few properties that architects and specifiers can test to know they are getting the right stone for the job. Water absorption is a crucial consideration as stones with higher absorption rates are more susceptible to mould, moss, pesticides and salt. Also, the flexural strength of a stone is important as it gives an indication of the stones overall durability. Measured in megapascals (MPa), the higher the number, the less chance it has of failing or delaminating once in-situ. Frost resistance should be measured and is particularly important for the UK market. Most natural stone is very resistant to frost but it can sometimes weaken the stone. Its resistance to frost is therefore measured by a percentage reduction in flexural strength after a cycle of freezing and thawing – the lower the number, the better. Some suppliers of natural stone have actually developed simple visual grading systems for their products so that customers can see this key information at a glance. This grading however must be based on CE testing results and not any in-house testing methods. Another key consideration when choosing hard landscaping materials is style. Real stone is an attractive material that offers a wide breadth of design possibilities in both residential areas and urban spaces. Each piece of natural stone comprises a blend of colours and tones, which can be used to create completely bespoke installations – perfect for achieving a distinctive character. Cobbles and riven paving stones lend themselves to more traditional settings. The heritage of a location can also be easily reflected in the choice of natural stone. Granite sets or sandstone with earthy tones and more textured surfaces, for example, would suit a town with an agricultural history. For a more cosmopolitan area or modern look, sawn sandstone or smooth limestone with clean lines and contrasting colours would be a better match. In addition, as the colour in stone is natural and not artificially pigmented like concrete, it can also help create a much warmer and more organic finish.
BP 10 October 2016
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