Top Tips For Specifying Natural Stone Paving
This article was first published on Natural Paving
Hard landscaping is becoming increasingly important as both the public/commercial and private sectors face the challenges of urbanisation. Here Malcolm Gough, Group Sales and Marketing Director at Natural Paving Products (UK) Ltd 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 per cent by 2050.1 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 manufactured 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 a few properties that architects and specifiers can test to know they are getting the right stone for the job.
The first is water absorption. This is a crucial consideration as stones with higher absorption rates are more susceptible to mould, moss, pesticides and salt. Secondly, flexural strength of a stone is also 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.
Finally, 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 unique 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.
Something else architects and specifiers should consider is the sustainability and ethics of the products used. Using a trusted natural stone supplier is the only way to ensure that materials are responsibly sourced. Much of the natural stone used in the UK is imported from overseas and in particular India, which is one of the main exporters of sandstone and limestone. While Indian stone can offer attractive products at cost effective price points, regulation of its stone industry is erratic, with corruption, child labour and illegal quarries presenting major problems.
One safe way of specifying with integrity is to use a stone importer that has complete end-to-end control of the supply chain, from quarry to doorstep, and can provide documentation for each step and component. Also, architects and specifiers can check whether the supplier is a member of the Ethical Trading Initiative (ETI) – an alliance of companies, trade unions and voluntary organisations that work in partnership to improve the lives of poor and vulnerable workers across the globe.
Natural Paving Products, for example, is one of the few companies that can offer this assurance as it has invested in establishing its own quarries. The company owns seven Indian quarries, is partner in two others and has recently invested significantly in two state-of-the-art factories, meaning it has full control over the products it supplies from the point of extraction, to end delivery.
Adding to responsible specification, architects and specifiers should always look for products that are fully CE marked as inaccurate or even fake product labelling can mislead customers about the long-term performance of products. However, the significant cost of becoming fully CE Marked has led some of the smaller players in the Indian stone market to apply incorrect labels to their products and pallets. Specifiers should therefore carefully examine the quality marks provided by manufacturers and take appropriate steps to ensure any documentation is genuine.
Finally, natural stone installations are a significant investment, so it makes sense to consider using specialist protection products, which can further improve its durability and resistance to staining. Sealants are best, as opposed to coatings (which sit on top of the surface), as they are designed to penetrate deep into the substrate to offer longer lasting protection. Equally, it is worth using a breathable sealant as this means it can be applied straight after installation, providing protection straight away. Manufacturers of some un-breathable sealants recommend that they must only be applied three months after installation, allowing for any efflorescence to appear, but this leaves the stone vulnerable to the elements.
It is also worth looking for a sealant that will provide protection against both water and oil based contaminants. Landscaped areas treated with high quality sealants like this actually become self-cleaning to an extent, as rainwater can wash away most materials that cannot penetrate into the stone and are left on the surface.
Natural stone is an ideal material in an increasingly urbanised environment and by taking all of these considerations into account, architects and specifiers can make the best decisions about their choice of material for their project.