GRC FAÇADE CLADDING
Since its development in the late 1960s, glassfibre-reinforced concrete (also known as GRC and GFRC) has steadily gained popularity as a façade cladding with architects, engineers, contractors and developers throughout the world. However, as the material moves towards its 50th anniversary, more and more construction professionals are becoming aware of the benefits of using this remarkable composite.
GRC’s growing popularity is based on its virtually unlimited versatility, offering designers the possibility to provide external cladding in panels in both rectangular and complex curvilinear shapes. Unlike many other types of cladding, GRC offers the opportunity to provide buildings with a sense of solidity without the associated issues of weight and environmental concerns.
GRC is available in a range of architectural finishes, textures and colours. The material can be manufactured to resemble natural stone with a variety of finishes from a fine grain to more exposed coarser aggregates. If required GRC can be highly polished to provide a surface texture similar to that of a polished worktop – indeed the material is often used for this application.
Stone dressings have been used for many centuries on private and commercial buildings. However, by the late 19th Century the cost of natural stone prompted a growing trend towards stone substitutes. First developed a century earlier, these were becoming increasingly popular, offering the obvious cost savings of casting from one mould rather than the repetitive carving of components.
Although a variety of materials and techniques were developed, by the early 1900s the most popular was earth-moist or semi-dry cast stone. This technique allowed rapid production of identical features thus providing builders and developers with a low-cost alternative to natural stone that was virtually identical in appearance. Many fine examples of buildings constructed in the first two decades of the 20th Century still exist, with their cast stone ashlar masonry and architectural dressings having weathered exactly the same as those constructed from natural stone.
However, in the 1930s a trend began to develop to move away from traditional construction on many commercial developments, with reinforced concrete frames taking the place of traditional masonry. This, along with the increased use of a mechanised approach to building, allowed architects to start designing buildings with large areas of glazing thus providing the concept of the large open-plan offices we are familiar with today.
To complement this approach, large architectural cast stone panels were required that could be installed along with the new forms of curtain walling being developed. This was simply not practical with the semi-dry method and thus the period 1930–1960 saw the introduction of the precast concrete cladding panel whose use would dominate architectural stonework for the second half of the century.
Unlike semi-dry, these panels could be manufactured in much larger sizes and, with a virtually identical fine texture, became much more popular in commercial applications. While natural Portland and Bath stones were easily replicated in this new wet-cast process, a further benefit was the ability to use larger aggregates, which, after acid washing or grit blasting, provided deep, rich textures.
The benefits of precast concrete cladding panels were quickly recognised by the leading architects of the time such as Le Corbusier, who successfully used a combination of glazed curtain walling and precast concrete cladding panels in the 1930 Maison Suisse in Paris.
Of course, manufacturing such large panels was only possible by the use of reinforcing steelwork within the concrete matrix. While concrete is incredibly strong in compression it lacks tensile strength. The introduction of steel bars and cages allows the two materials to act as a composite offering a combination of high compressive and tensile strength.
In the latter half of the 20th Century, not only were commercial buildings being constructed using these modern methods of construction but also the swing towards high-rise residential blocks all over the world saw precast concrete cladding soaring in popularity. In the UK, most of the larger and longest established caststone manufacturers eventually stopped manufacturing semi-dry cast stone to concentrate on this new ‘wet-cast’ production method.
It was against this background that GRC was developed by Pilkington Glass and the Building Research Establishment. Seeing the benefits of the newly introduced glassfibre-reinforced plastics, which were being used extensively in the 1960s to manufacture among other things aircraft and cars, it was a natural step to look to use these fibres to reinforce concrete.
By 1969, the process had been perfected and was starting to be commercially manufactured. Unlike precast concrete, which has reinforcement placed in the tensile zones, GRC has its reinforcement spread throughout the matrix. The resultant composite can be manufactured as thin as 12mm, offering significant weight saving over precast. Of course the other major advantage is no possibility of corrosion to the embedded steel – a problem encountered with some precast of the time.
Over the next 30 years GRC technology was, like most British inventions, used primarily overseas, the UK being particularly slow to change, especially in the building industry. However, as the 21st Century dawned, the benefits of GRC were becoming increasingly difficult to ignore.
A new cast stone
Where GRC differs from both semi-dry and wet-cast stone is in its significantly higher flexural strength. This allows cladding panels and architectural dressings to be manufactured that are considerably lighter than their traditional counterparts without any loss of visual appearance. Of course this is of major importance in modern construction as it reduces the need for heavy lifting plant and imposed dead load of the building structure. The weight saving of a typical GRC cladding panel over that of an identical precast panel would be around 70–90%. On a project of, say, 5000m2 that could be a saving of as much as 800 tonnes of dead load.
A further benefit of GRC is the retention of supplied appearance over a longer period than both semi-dry and wet-cast stone. Semi-dry stone has a high porosity, which means it will weather in a very similar manner to natural stone. While in some applications this is an attractive feature, on most contemporary buildings it is simply not acceptable. Wet-cast does retain its supplied appearance longer; however, neither material can equal GRC for lack of required maintenance.
The best example of the weathering of GRC can be found in the 20-year restoration of Shepard Hall in New York where 72,000 GRC has been used to replace failed terracotta used in the original 1906 construction. GRC was selected after much research and has given the architects the opportunity to examine adjacent components produced and installed sometimes many years apart. The GRCA is soon to release a short video giving a deeper insight into this fascinating project.
GRC can be manufactured in a greater variety of shapes and sizes than either semi-dry or wet-cast stone. The spray process production technique, which is widely used on large-format cladding, allows the most complex shapes to be created, thus allowing the designer possibly the ultimate expression of freedom and form in architectural cladding. In addition, the high strength of the material allows for the most intricate of architectural detailing to be incorporated into the panels.
With sustainable construction being at the forefront of most architects’ minds, GRC can make a significant contribution. Cement production accounts for approximately 5% of the world’s CO2 emissions and any form of precast that reduces cement content has a positive effect on the environmental impact of any given building. Although GRC has higher cement content than either semi-dry or wet-cast, its lower weight reduces the amount of cement required to produce the panel. While a typical precast panel will contain around 50–60kg of cement per square metre, the equivalent GRC panel will only contain approximately 25kg.
GRC is truly coming of age with a general worldwide acceptance as a primary cladding material. After exhaustive research, testing and analysis over the past 40 years it is apparent that GRC is a very durable material. Very few building materials have been as closely examined as GRC, with the result that it can confidently be specified and used on the most demanding of projects.
In the United Arab Emirates, where environmental conditions can best be described as aggressive, GRC is being used as a primary cladding material on large-scale developments. Foster and Partner’s Masdar City some 17 miles from Abu Dhabi is a 6km2 development with an emphasis on sustainable design and features some unique GRC cladding. Fellow internationally acclaimed architect Zaha Hadid has specified some 70,000m2 of GRC façade cladding on the KAPSARC project in Saudi Arabia currently under construction.
In South Africa, the 2010 World Cup Final between Spain and The Netherlands took place at Johannesburg’s Soccer City Stadium built the previous year and featuring a distinctive multi-coloured external cladding – all in GRC.
Throughout Turkey, Russia and the former Soviet states GRC is now widely used – Istanbul features probably more GRC cladding than any other city in the world. Likewise, when Zaha Hadid designed a futuristic private resistance near Moscow that had to withstand severe snow loading to the horizontal cladding, again GRC was the material of choice.
The UK is also now no stranger to the use of GRC. The Olympic Village in Stratford was constructed using large quantities of GRC where precast concrete was simply not practical. The vast new Crossrail project, which will run across Central London, will feature GRC cladding at virtually all the new stations, chosen not only because of its durability but also its proven use in similar projects all over the globe.
The use of GRC in China is extensive with many large and prestigious national projects using GRC as a building skin cladding. Tian Jin Port and Huhhot in Inner Mongolia are typical of the extensive use of GRC with the use of 42,000m2 and 26,000m2 respectively. GRC is particularly popular in areas prone to seismic and hurricane activity, such as New Zealand, Australia and USA and who have strong markets for the material.
Versatile and durable
GRC is one of the most durable and versatile methods of replicating natural stone in large format cladding panels. There are few challenges to which a high-quality GRC manufacturer cannot rise, offering truly innovative building solutions on projects across the world.
From small rainscreen cladding panels to 30m2 complex curvature building envelopes, GRC offers the answer to any designer or architect wanting to recreate the timeless appeal of natural stonework on modern and contemporary projects.
The International GRCA has over 60 manufacturing members in over 20 different countries, with new organisations joining every month as the demand for this remarkable composite continues to grow.
Based in the UK, but with an international membership, the GRCA offers a technical advisory service as well as being able to connect potential specifiers and users of GRC with manufacturers, engineers and consultants to assist them in all elements of GRC façade design, fabrication and installation.