Rory Kendrick, Marshall's International Natural Stone Sourcing Director, explained that there are three key factors that must be considered when determining whether to invest in bringing a stone from the ground into the marketplace - water absorbency, flexural strength and frost resistance. And the same three factors need to be considered by consumers (you and me) when deciding which stone to purchase;
· Water absorbency - A stone with high water absorbency will not only turn green, (a common consumer complaint with sandstone patios) but may also be more susceptible to frost action which will degrade the stone.
· Flexural Strength - In terms of flexural strength, a stone with poor strength means that the product could be easily damaged in transit, during the installation process, or simply by everyday use.
· Frost Resistance - It’s also important to consider frost resistance. A stone that loses strength when subjected to repeated frosts is far more likely to fail.
There is a British Standard that covers these issues. The design and installation standard BS7533 part 12 covers the technical performance of stone and applies to any external paving product. To ensure you select a stone which is technically up to standard, it is advisable to use a supplier that tests all its products and can supply you with an in-date test certificate, or declaration of performance (especially important for commercial schemes where heavy vehicle movements are likely). If a supplier is unable to supply these details there’s no guarantee that their stone is technically sound, as is often the case with some of the imported Indian Sandstone.
At Marshalls they have tested all their stone to be 100% sure that every single one meets or exceeds the British Standard, and called it The Stone Standard. No matter how beautiful the appearance, anything that does not meet the grade is rejected, sometimes meaning that a newly found quarry is thoroughly investigated, but never actually worked by Marshalls at all.
“We want consumers to be pleased with our products” explained Rory. “We’ve created The Stone Standard to explain the process to people in an easily accessible format. We know, from laboratory testing that other companies are releasing products into the marketplace that don’t meet this standard. Being fit for its end purpose is the most important quality we look for when we decide to bring a particular stone into the marketplace.”
Not only do the laboratory tests ensure that specific qualities are met, but Marshalls also spends time creating trials of products before they release them – their ground is awash with trial patios, making sure that the stone can stand the tests of weather and time. Only when they are satisfied with the product will it finally make its way into the pages of their catalogue.
Visit the Marshalls Stand EA60 at RHS Chelsea to find out more.
Read tomorrow's BLOG to discover the amazing process of transformation which takes place from quarry to patio.