As one of very earliest materials to be used for construction purposes alongside timber and clay, natural stone can provide modern buildings with aesthetically timeless as well as sustainable and resilient exteriors when employed as external cladding.
While it's not always feasible to create entire built structures from natural stone in the modern era, the use of stone materials as external cladding can confer new buildings with a refined and timeless appearance while also diminishing their carbon footprint and significantly enhancing their ability to withstand the rigours of time.
Thin panels made from natural stone are becoming increasingly popular in some markets as the primary covering material for building envelopes, essentially serving as a substitute for cladding panels made from materials such as glass-fibre reinforced concrete (GFRC) or fibre-reinforced polymer panels (FRP).
Natural stone possesses a number of key advantages when used for external cladding purposes, particularly compared to modern materials that are more commonly attached to building exteriors.
Chief amongst these advantages is perhaps aesthetic appearance; natural stone has been employed as building material since time immemorial, and can confer the exteriors of modern buildings with an elegant, timeless appearance.
Another obvious advantage is resilience, as stone is amongst the hardiest of all building materials and a veritable byword for strength and durability. The resilient nature of stone is amply demonstrated by the fact that it's a constituent material for the world's most ancient built structures that are still extant today - from the Great Pyramid of Giza to the Athenian Parthenon, from Yemen's Marib Dam to Gobekli Tepe in Turkey.
This resilience can dramatically reduce the repair and maintenance requirements for the exteriors of new buildings in the modern era, and owners can depend upon the material to endure throughout the full life cycle of their properties. The inherent durability of many forms of stone also means that it does not require the addition of any further finishes or coatings.
Another advantage, and one which stone shares in common with other natural building materials that have been widely used since pre-antiquity such as timber and clay, is its low environmental impact.
The manufacture of natural stone products entails little more than excavation of material from the earth and a modest amount of processing in the form of slabbing and cutting for conversion into a usable form.
This means that natural stone has significantly lower levels of embodied energy - which is a proxy measure for the carbon emissions involved in the creation of a product - compared to artificial building materials such as concrete or polymers, whose manufacturing processes are far more energy intensive.
Designers and builders must still exercise caution when opting to use stone as an exterior cladding, and should give consideration to a number of factors that can significantly affect its performance.
An issue of key importance is the anchorage method used to attach the stone cladding to the building, as well as the type of backup material employed.
Given the weight of stone, builders should ensure that anchorage system can independently bear the weight of each unit, and should refrain from stacking the cladding panels upon exteriors.
All anchorage parts should be made from high-grade stainless steel, particularly in maritime environments where metal components are more susceptible to corrosion. The use of strong, corrosion-resilient components will hopefully ensure that the anchorage used to keep natural stone cladding in place can last as long the mineral materials themselves.
When it comes to backup materials, concrete is perhaps the best choice given that it possesses the greatest anchorage capacity and permits the installation of anchors anywhere on the material, which provides for greater flexibility of design and installation.
The use of metal studs should be avoided when installing natural stone panels upon exteriors because they do not provide a high level of anchorage capacity or a long anchorage service life, as the anchor must penetrate the metal stud, which can weaken corrosion resistance at the cutting point.
Steel sub-frames and pre-panelized sub-frames are also viable options, although these must be designed specifically to hold the anchors for the stone panels in the appropriate locations if they are to be fully effective.
Responsiveness to environmental factors is another consideration of primary importance when using stone for external cladding purposes. Different stones are suited to different climate conditions, as they react differently to factors such as pollution levels, exposure to sea water and extremes of cold or hot temperatures.
For this reason, it's important to look at the ASTM testing data that accompanies most stone building products on the market, which will cover factors including absorption, density, abrasion resistance, compressive strength and flexural strength. This will enable designers and engineers to fully ascertain the suitability of a stone product for a given building project.