The Potential Role of Cattail-Reinforced Clay Plaster in Sustainable Building
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The potential role of cattail-reinforced clay plaster in sustainable building G. Georgiev, W. Theuerkorn, M. Krus, R. Kilian and T. Grosskinsky Fraunhofer-Institute for Building Physics IBP Holzkirchen, Germany _______________________________________________________________________________________ SUMMARY Sustainable development is a key goal in town and country planning, as well as in the building industry. The main aims are to avoid inefficient land use, to improve the energy efficiency of buildings and, thus, to move towards meeting the challenges of climate change. In this article we consider how the use of a traditional low-energy building material, namely clay, might contribute. Recent research has identified a promising connection between the reinforcement of clay for internal wall plastering with fibres from the wetland plant Typha latifolia (cattail) and the positive environmental effects of cultivating this species. If large quantities of Typha fibres were to be used in building, the need for cultivation of the plant would increase and create new possibilities for the renaturalisation of polluted or/and degraded peatlands. We explore the topic first on the basis of literature, considering the suitability of Typha for this application and possibilities for its sustainable cultivation, as well as implications for the life cycle analyses of buildings in which it is used. We then report (qualitatively) the results of testing different combinations of clay with natural plant (straw and cattail) fibres for their suitability as a universal plaster, which demonstrate clearly the superior properties of Typha fibres as a reinforcement material for clay plaster mortars. KEY WORDS: clay mortar; life cycle analysis; paludiculture; peatland; Typha latifolia; wetland _______________________________________________________________________________________ INTRODUCTION clay has already been proved as a sustainable building material. If it is extracted and used directly Clay usually forms by secondary sedimentation in from the construction pit, there are hardly any low-energy depositional environments such as large manufacturing or transport costs, and it can be re- lakes and marine basins, and can easily be found on used many times without losing functionality building sites. It is a versatile building material that (Schroeder 2010). requires no special preparation, and consequently There are clear needs and demands (and, has a long (ca. 8000 years) history of use in various therefore, markets) for continuation of the construction techniques (half-timbered, rammed traditional construction techniques in which clay has clay, wattle and daub etc.). There are currently been a prominent material. According to Manfred around 2.2 million clay buildings in Germany Gerner, member of the executive board of (Lehmschwalbe 2013), some of which are several Arbeitsgemeinschaft Historische Fachwerkstädte centuries old. (Working Committee of Historic Half-timbered The Industrial Revolution of the 19th century Building Cities), approximately one-quarter of the brought new manufacturing and processing 2.4 million half-timbered buildings in Germany are technologies that enabled the development of a new listed as historic buildings. After being unoccupied generation of building materials including bricks, for long periods, they are in such poor condition that which largely replaced clay in construction until the demolition is frequently the only viable course of debate on sustainability was opened. Nowadays, the action (Göres 2010). In other words, the number of use of unlimited energy by industry is no longer traditional buildings in need of affordable acceptable or affordable against the backdrop of rehabilitation in Germany is very high. Figgemeier global energy and oil crisis. Sustainability is a & Knoffel (1993) point out that, since clay was primary focus in building, and research is seeking superseded by bricks, it has been increasingly out new materials with lower manufacturing costs, noticed that the thermal, sound and impact sound higher energy efficiency and life-cycle sustainability insulation of traditional buildings cannot be (Schroeder 2010). Usually, the life cycle of the achieved by a normal one-layer truss façade. whole building is considered and analysed, then Therefore, the goals of a restoration project should concepts are developed for energy optimisation. include the preservation of the original structure of Although frequently neglected in this context, the building and the integration of traditional Mires and Peat, Volume 13 (2013/14), Article 09, 1–13. http://www.mires-and-peat.net/, ISSN 1819-754X © 2014 International Mire Conservation Group and International Peat Society 1 G. Georgiev et al. CATTAIL-REINFORCED CLAY PLASTER IN SUSTAINABLE BUILDING materials into modern materials systems. Some be used in building, the need for cultivation of the relaxation of the restrictions imposed by energy- plant would increase and create new possibilities for efficiency regulations may be required. The cost, the renaturalisation of polluted or/and over-used effort and time required to renovate traditional peatland areas. In this article we explore the buildings could be reduced by devising standardised potential contribution of Typha to this new avenue maintenance measures, based on a thorough for sustainable building, and outline the results of understanding of the fundamentals of traditional some preliminary tests of its performance as a construction, that tradesmen and craftsmen could reinforcement material for clay plasters. apply to achieve total solutions in the future. Independently of the historical use of various infill materials (including clay) in half-timbered POTENTIAL OF THE CATTAIL PLANT buildings, clay mortars were (and still are) very frequently used as interior plaster. It has long been Suitability for use in building materials understood that clay plasters create a pleasant design Typha or cattail (Typha latifolia) is a rhizome- and haptic (tactile) effect and, at the same time, forming grass-like plant that grows naturally in efficiently solve indoor climate problems on account swamps and marshes, as well as on the banks of of their capacity to absorb humidity (Eckermann & slow-flowing rivers. It typically reaches a maximum Ziegert 2006). Moreover, they are generally height of two metres, or up to three metres under recognised by building owners as ‘ecological’ and optimal water level conditions (Figure 1A). It healthy, capable of introducing a desired element of reproduces vegetatively from spreading rhizomes as ‘naturalness’ into modern constructed environments. well as from seeds, which are borne on a distinctive Because clay plasters are now applied in new spadix (Figure 1B,C). As an adaptation to its aquatic buildings as well as in old ones, demand has habitat, the plant has a high polyphenol content, increased (Claytec 2013) but, despite their great which makes all of its parts highly resistant to popularity, they are still too expensive. If the mildew and bacterial infections (Heinz 2010). manufacture of clay products could become more Typha has many potential uses (Access cost-efficient, they would be used more frequently Washington 2013), and very high potential for the in the future. To achieve this goal, both researchers building industry, due to its physical structure. and the industry are investigating the properties of Because approximately 85 % of the plant mass clay and various clay material compositions, with a consists of aerenchyma tissue, the leaf mass has view to improving their practical application in high porosity (Figure 1D), a (low) density of building and developing sustainable industrial approximately 30 kg m-3, and lower thermal production methods. conductivity (λ = 0.032 W m-1 K-1) than polystyrene The beneficial properties of clay are maintained (λ = 0.04 W m-1 K-1). Highly efficient insulation only if no synthetic materials or stabilising boards can be produced by combining the leaves substances are added. However, depending on the with a simple mineral binder (magnesite). A composition of the material originally excavated, significant advantage of using cattail biomass as various natural fibres and sands can be added to thermal insulation is the very low production of create a clay mortar with the desired physical dust. Cattail leaves can also be used as reinforcing properties. The next challenge is to discover how to fibre for various building materials. achieve clay plasters with perfect properties for The seeds account for approximately one-quarter universal application. of the total dry mass. The so-called “seed A current focus of our research group is to parachutes” are very light and their structure inconspicuously reinforce clay plasters by adding (Figure 1E) is such that they create a strong network natural plant fibres. We aim to develop a solid and when mixed into clay mortar. When they are added strong ‘universal’ humidity-regulating clay plaster. as reinforcing fibres to lean clay plaster (with a low It would be a great step forward for sustainable clay fraction), the strength of the plaster is improved building to develop a plaster composition that would (Müller-Sämann et al. 2003). be suitable for use in the preservation and/or restoration of ancient monuments and historic Prospects for cultivation buildings as well as in new buildings. Our research The high polyphenol content of the Typha plant has identified a promising connection between the makes it not only a durable