Materials scaling new heights

Materials World magazine
1 Aug 2017

As climbing is made an Olympic sport, Kathryn Allen looks at the materials used in artificial climbing walls. 

In August 2016, climbing was made an Olympic sport following a campaign led by the International Federation of Sport Climbing (IFSC). The 2020 Olympic Games, to be held in Tokyo, Japan, will feature three climbing disciplines – speed, lead and boulder. While the latter involves climbing walls of up to 4.5m, both speed and lead climbing require walls of up to around 15m, with attachment points for ropes. 

Climbing has become increasingly popular, with indoor and artificial climbing walls meeting the needs of climbers who do not have the access or desire to climb outdoors. Indoor climbing walls were originally designed to offer facilities for climbers to practice during winter months when the weather prevented them from climbing outdoors. 

Don Robinson, a physical education lecturer at the University of Leeds, UK, is generally credited for creating the first modern indoor climbing wall in the UK in 1964. But artificial walls were built prior to this – a wall featuring holds made of iron rungs was built in Milan, Italy, in the 1920s and the outdoor Schurman Rock, made of natural rock, in Washington, USA, in 1939. Robinson’s wall was made of brick, with sections removed and either left as openings or filled with natural rock to create holds. Material use and design developed, and in 1987 the USA’s first commercial, indoor climbing gym opened in Seattle. The climbing walls at Vertical World, which remains open today, were then made of sections of real rock glued to painted plywood panels.  

In 1991, the UK’s first commercial indoor climbing wall was built in Sheffield in an old steel foundry. The Foundry sees its busy months from September to March, when wintery conditions keep climbers indoors. There has, however, been a surge in climbers who climb indoors only, as its own sport, according to Karl Bacon, climber and employee at The Foundry. The inclusion of sport climbing in the Olympics can only increase this interest in indoor and competition climbing. Statistics from the IFSC show that 25 million people are climbing regularly and the IFSC 2016 World Championships in Paris saw 533 registered athletes and 20,000 spectators. 

Real-rock-imitation walls 

Having moved away from the original brick or breeze block walls, there are two main types of artificial climbing walls used today – plywood and rock-effect walls, which are made from concrete or glass-reinforced plastic (GRP), also referred to as fibreglass – all of which must comply with the European Standard for Artificial Climbing Structures (EN 12572). 

Real-rock-imitation walls fall into two main categories – coated walls on a fibreglass base or the less common shell concrete structures. The former is used both indoors and outdoors, while the latter is mostly used outdoors. These wall systems offer a climbing experience similar to natural rock and are durable, with life expectancy dependent on weathering and use, and easy to clean. The concrete is either sprayed or moulded by hand, with features such as flakes, cracks and ledges incorporated into the main structure, while the fibreglass wall systems are coated using a thick mixture of resin and aggregates or, for a less textured surface, sand and paint. 

Alasdair Hannah, Senior Designer at Entre-Prises Climbing Walls, said of manufacturing shell concrete walls, ‘a shell of concrete [is formed] on an underlying substrate, which supports the concrete until it is cured. Application of the concrete could be by hand on a small project or by spraying. On a non-structural project where the loads are smaller, the substrate could be blocks of polystyrene carved roughly into the shape of a boulder. Whereas, on projects where higher loads need to be considered, the substrate would be more akin to a mesh of reinforcing bar possibly fixed to a steel frame.’ Hannah explained that engineering shell concrete walls can be difficult as it is not always clear how loads will be distributed throughout the structure due to its complex shape. The concrete is therefore often not deemed a structural load-bearing element and base structures are used. The concrete is sprayed using a hose at high pressure. One of two mixtures is used – a dry mix of cement and aggregates, with water added at the application stage, or a wet concrete mix. 

The popularity of real-rock effect walls has, however, decreased in recent years. Adam Koberna, President of Walltopia USA, said, ‘I think shell concrete has seen its day […] I would say that up until five years ago the industry was driven by fibreglass walls, but lately everything has moved to plywood. The realistic rock-look is definitely at the bottom of the list of desirable materials for clients.’ As indoor climbing becomes a sport in its own right, the flexibility and low cost of plywood is taking priority over mimicking natural rock. 

Real-rock-imitation walls are more limiting than plywood. Route setters – who position holds on the walls to create climbs of varying grades – are restricted with these wall systems as the very uneven surface and built-in features limit where holds can be placed. Rob Adie, Climbing Walls and Competitions Officer at the British Mountaineering Council (BMC), UK, says, ‘Fibreglass and concrete [walls] are harder to manufacture, requiring the careful mixing of resins and chemicals and then the careful manipulations of the features both in the factory and at installation.’ This results in these wall systems being more expensive than alternatives such as plywood. While concrete and fibreglass walls will generally outlive plywood ones, environmental factors and use can affect the lifespan. Also, if there is a lot of movement in fibreglass walls, the structure can be damaged. 

A move towards plywood 

The generally cheaper plywood panel wall systems have grown in popularity in recent years, as interest in indoor climbing has increased and the sport has become more concerned with leisure and fitness. 

Plywood is made of two or more layers of wood, glued together with the grains at differing angles to increase strength. The 18mm plywood panels are fixed to a steel or timber supporting structure depending on the height, requirements of the wall and the manufacturer. Often manufactured using computer aided design (CAD) and computer numerical control (CNC) methods, the panels can be made to a high degree of accuracy in a shorter timescale. Their modular design and construction method also reduces installation time. 

Plywood panel walls, often made from Baltic birch plywood or marine plywood, also offer climbing wall manufacturers flexibility, allowing more holds to be fixed to the walls and moved around easily. However, while marine plywood is designed to be more durable and resistant to biodegradation than regular plywood, walls made from this material are generally not suitable for outdoor use due to the UK’s damp climate. 

Climbing wall manufacturer Entre-Prises, UK, has looked at alternatives to plywood, including the environmentally conscious Ecosheet, made from recycled plastic, originally intended for building site hoardings. However, this material was not strong enough for holds to be bolted on securely due to its sponge-like core. 

The Foundry has plywood walls backed onto a steel supporting frame for its lead or roped walls, measuring 10–15m in height, and resin panels for its bouldering wall, which stands just under 5m high. Discussing how easily volumes – large detachable features – and holds can be moved around on plywood walls, Bacon said, ‘This changes the shape and nature of the walls so, from a climbing perspective, it's far more interesting. The resin feature walls don’t offer flexibility.’ A lot of the plywood panels at The Foundry are the original 1991 panels, demonstrating the lifespan of 18mm-marine plywood. 

Stephen Skinner, Climbing Wall Coordinator at The Lock Climbing Wall, UK, explains that the placement of T-nuts, used to attach holds, can be closer together on plywood walls than on real-rock imitation walls, and that the uneven surface of the latter prevents holds sitting properly on the wall’s surface. There has been a trend among new climbing facilities to use screw-only holds on plywood walls rather than T-nuts, giving more freedom to route setters, as screw holds can be drilled as required and placed next to each other, while T-nut placements are pre-determined, Skinner says. This does, however, cause damage to plywood walls over time from repeatedly drilled screw holes. 

Hold on tight 

The first bolt-on holds to be marketed commercially were made by Entre-Prises, founded by climber and industrial engineer Francois Savigny in 1985, and were made from resinous concrete. Since then, holds have developed and are now made predominantly from polyester resin or polyurethane, and bolted or screwed onto the walls. Some training aids and volumes are made from wood or fibreglass. 

Polyester resin holds are cost effective, being widely available and relatively cheap, and have a texture favoured by climbers because of its dryness. However, they are hard, brittle and prone to chipping. Hannah said, ‘Hold manufacturers will add a variety of aggregates, which might include various grades of sand, flue ash, powdered calcium carbonate, and other “secret” ingredients to bulk out the resin.’ The addition of these materials keeps costs low but impacts the hold’s feel and strength. 

In recent years, the lighter and tougher polyurethane has become increasingly popular as an alternative to polyester resin. It is possible to make much thinner bolt-on holds with polyurethane, which would crack on installation if made from polyester resin. However, polyurethane is more complex to manufacture and does not usually feel as rock-like as polyester resin holds, according to Hannah. It also loses its friction, polishing up quicker than polyester. 

Despite this, Koberna said that most climbing centres in the USA use polyurethane, with polyester’s lasting use in Europe down to climbers who prefer its texture. However, both polyester resin and polyurethane holds are still manufactured, with the continuing development of polyurethane holds giving them a texture more akin to real rock. 

Material use for holds has also developed with attempts to improve efficiency and reduce environmental impact. Hold manufacturer Composite-X, Bulgaria, has developed a new hold material, Dannomite – a polyurethane and polyurea hybrid, designed to have a higher wear resistance and strength, cracking less than current materials. In 2009, hold manufacturer Nicros, USA, began using a renewable corn/soy-based resin in its Super-Mix recipe. 

Causing friction 

While competition walls are often not surface coated, ensuring climbers use only the set holds and do not rely on the wall itself for friction, coatings are generally applied to most commercial plywood or fibreglass walls. According to Koberna, 95% of the walls manufactured by Walltopia are coated. These coatings can mimic real rock, prevent holds from spinning easily and provide friction for climbing progression. 

The coatings are usually made from polyester resin or other hardwearing resins, and grades of sand mixed with paint. The proportions of materials and the application process depend on the desired effect and wall material beneath. Rock-effect fibreglass walls may be coated by hand with a thick mixture, made up of resin and fragments of rock and sand, that is moulded to create features. However, plywood or fibreglass walls, not attempting to mimic real rock, may just be coated with a sand-based paint. A mix of sand-paint and resin would only be applied to pre-cut plywood, as the coating would make the wall panels harder to cut were adjustments required on-site, as Skinner explains. 

Alternative climbing walls 

As climbing becomes more popular and moves away from real-rock imitation walls, centres such as Clip ‘n’ Climb and Funtopia have been established in various locations. These brightly coloured climbing walls are aimed at the general public rather than experienced climbers, and incorporate steel, moulded plastics, medium-density fibreboard and LED lighting in the walls. To make these centres more attractive the plywood walls are printed on. Koberna explains, ‘It's proving a cost effective way to create different appearances. A client can choose from pre-designed and engineered sections of printed plywood [...] The use of printing in wall systems is the next big thing for us.’ Wall manufacturers have also begun printing surface coatings, for example Walltopia has printed wood grain onto plywood panels to create texture as an alternative to coating the walls manually after manufacture. 

Augmented climbing walls also demonstrate the industry’s adaptation to an increase in popularity and technological developments, using interactive graphics projected onto the walls to create games for climbers. These systems do not require a change in the wall material, relying on projectors, sensors and computers, and walls that are lighter, more mobile and versatile in design, according to Sven Rösch, of Augmented Climbing Wall, a company spun out from Aalto University, Finland. Rösch said, ‘The technology uses projected graphics, proprietary body tracking and sophisticated depth recognition. That way the material of the wall panels is irrelevant as long as it is very light. It’s the same for holds – they will be recognised based on their distance from the sensors in the projector unit.’ 

The durability of these alternative wall systems, in terms of popularity, remains to be seen. Skinner was sceptical, saying, ‘I personally don’t see any of these emerging technologies becoming commercially viable other than as add-ons to already existing facilities.’ However, the increasing popularity of climbing has already changed the materials used for wall systems, as they move away from real-rock imitation to those that promote ease of training and flexibility. Materials development has kept up with the modern climber’s demand for dynamic climbing centres.