15.02.2014 - Ausgabe: 1/2014

Sports field renovation: Synthetic or natural grass?

Natural grass – the evergreen

Natural grass pitches set standards for functional properties and quality of use and are widely preferred by players. According to DIN 18035/Part 4, a natural grass pitch is a biological playing surface which has a natural vegetation cover, strongly anchored by roots. As a dynamic playing surface the natural grass provides shear strength, elasticity, impact absorption and controlled rolling and bouncing behaviour of the ball. A natural grass pitch is made up of the grass cover, supporting substrate and a drainage system and is the standard against which all other playing surfaces are measured. A well-maintained natural grass pitch has an unlimited playing life as it can be repeatedly regenerated. At the same time however, this feature is also the biggest disadvantage as it demands higher maintenance care. Not only must the grass be cut regularly, it must also be sanded, aerated, fertilised and re-sown. This work requires a fleet of specialised machinery and plant products. Usually the care and maintenance work is carried out by the local community authorities or specialised ground-care contractors, which naturally involves further costs. As a living ecosystem, natural grass is also an attraction for living things of all kinds. Moles, worms, insects (larvae) of all kinds, fungi, moss or weeds; the grass pitch needs to be protected from all these pests. Severe storms, sustained periods of heavy snow or drought have a negative effect on grass playing areas. And when corresponding protective measures not help, a grass pitch needs above all rest and recuperation, much to the disappointment of the players.
Synthetic turf – Breakthrough in the third generation

As an alternative to the natural grass, synthetic turf was developed during the 1960s. While, for example, hockey players quickly accepted this playing surface and today hockey has to a great degree converted to synthetic turf pitches, the materials of the first and second generation were disliked and criticised by footballers. Unpredictable ball behaviour, special shoes, more tiring and a higher danger of injury from the coarse, strong turf fibres which could even cause friction burns, led to the first installed pitches being replaced again. It was not until the end of the 1990s that a further developed synthetic turf, the so-called "Third Generation" slowly became accepted as a suitable football pitch surface. The new developments such as longer, softer pile fibres, rubber granulate and quartz sand filler and improved elastic substrate layers made the playing properties of the synthetic turf much more similar to natural grass. Since then, synthetic turf has advanced in leaps and bounds, above all in amateur sport and geographical locations with difficult climatic conditions.
Depending on the kind of sport for which it is intended, a synthetic turf pitch must also satisfy many rules and regulations. Along with the DIN EN 15330-1 standard, DIN 18035-6 and -7 (currently withdrawn) are mainly responsible for the specifications for a synthetic turf pitch and its construction. Synthetic turf pitches are made up of several layers of material. On top of this the actual synthetic turf is then laid in pre-manufactured strips similar to a pile carpet. These are manufactured using a tufting process and filled with different materials depending on the pile height and intended sport use. Hockey pitches have short fibre tufts and are often used without filler material as they are watered before use. Tennis courts have short fibres and a large amount of quartz sand filler; football and rugby pitches usually have significantly longer fibres and are partially filled with sand or rubber granules. Multi-functional pitches are also possible. There are many different versions using different types of fibre and different kinds of rubber granules with in some cases greatly varying qualities, properties and life expectancy.
Synthetic pitches also require regular care and maintenance work. Along with weekly sweeping of the pitch as well as loosening and even distribution of the filler material, pitches need an annual "deep cleaning" as well as regular removal of coarse dirt, leaves, weeds and twigs. A synthetic pitch can also be damaged by growth of moss, lichens and algae as well as sand imported from neighbouring sports facilities, chewing gum, cigarettes, dust and lubricating agents from the maintenance equipment. A well-maintained synthetic turf can be used intensively and last up to 15 years before the turf layer needs to be replaced.
When is which synthetic turf worthwhile?
For the majority of users, an optimally maintained natural grass will remain the preferred choice of playing surface, even though synthetic turf now has very similar properties to the original thing. From the point of view of installation costs, a conversion to natural grass (approx. EURO 200,000.-) is usually significantly less expensive than installation of a synthetic grass pitch (from around EURO 400,000.-). Maintenance costs of a natural pitch are however, usually three to four times higher than for synthetic turf. Another important factor is that a natural grass pitch can only be used for around 400 – 800 hours each year while the use of a synthetic pitch is around 2000 – 2500 hours or more. This is above all an advantage for larger clubs with many junior teams or offering different kinds of sport. In addition, the maintenance costs per playing hour are strikingly lower. All-weather use and improved playing conditions in poor weather are also points in favour of synthetic turf. For clubs looking to provide top-level sport, who do not need to obtain maximum use of the playing field and who have the possibility of professional care and maintenance, a natural grass pitch is the best choice (except for hockey). In addition, a synthetic turf pitch will involve intensive renovation costs after 15 years at the latest as the turf layer must be completely replaced. Costly smaller repair jobs must be carried out on a regular basis. As however, the cost-benefit calculation is clearly in favour of synthetic turf and communities and clubs can offer much more intense use with this surface, it is probably that in future clearly more synthetic pitches than natural grass ones will be built.

Hybrid turf – The material of the future?
Development of turf playing materials continues. For some time now a combination of natural and synthetic turf has been available: Hybrid turf. This is already widely used in the NFL and English Premier League competitions. This kind of pitch has a basic layer of synthetic fibres sown with natural grass so that a playing surface with a high degree of natural grass blades is created. Hybrid turf has two major advantages: It is significantly longer lasting, is more winter resistant and installation costs are much lower than for a synthetic turf system. At 800 – 1000 hours, annual use is however, far below that possible with a purely synthetic pitch. Nevertheless it`s an interesting alternative.

The question of the optimal sport playing surface remains difficult to answer. Each individual case must be analysed on its own merits and taking into account different points of view. Many sports fields constructors offer both natural grass and synthetic turf systems and hybrid turf is also increasingly available. One thing is certain however, the days of the unpopular clay courts are finally numbered. (TT)

Photographs and support from:
Hermann Kutter
Landschaftsbau-Sportplatzbau GmbH & Co. KG
Buxheimer Straße 116
D - 87700 Memmingen, Germany