Innovative textiles and functional membranes for use in energy-optimized cladding systems
The textile industry offers numerous high-tech products that could provide solutions to many problems in the domain of building physics where conventional systems deliver only some of the desired results - or none at all. Typical examples include the materials used to create well-known outdoor products that combine extreme breathability with good rain protection, plus fabrics treated with dirt-resistant coatings or containing antimicrobial fibers. In terms of structural durability, textiles can surpass the performance of even high-quality plaster systems. Another advantage of textile materials in this context is their outstanding elasticity. This property eliminates certain problems typically associated with plaster façades, such as the formation of cracks due to stress caused by fluctuations in temperature or moisture content. The most common method currently employed to improve the energy efficiency of existing buildings involves the use of external thermal insulation composite systems (ETICS). The aim of our investigations is to study the viability of replacing the conventional plaster used in ETICS with an appropriately-modified textile product.
Choice of textile and textile composite structure
When choosing a suitable textile fiber as the basis or substrate for a modification, one of the first things to consider is the desired properties of the future composite structure. These properties largely depend on the raw material from which the fibers are made, the type of textile shaping process employed and the type of surface treatment. The aim is to develop a textile composite structure that exceeds the requirements of conventional render systems and exploits the characteristic advantages of textiles in the new application as a substitute for plaster in an ETICS. The table below lists the criteria that need to be taken into account. When deciding on which textile composite materials to test, care was taken to include a wide range of different products with varying physical properties. This enabled them to be distinguished in terms of their propensity to soiling and support of biological activity. The choice of different finishing techniques for the textile building components was based on the objective of protecting the façade in which they are incorporated against soiling by airborne dirt particles such as soot, pollen, etc., and biofilms such as algae and similar organisms. The finishing techniques employed included both typical processes used in the textile industry and newly-developed processes.
Two techniques were used to give the systems dirt- or water-repellent properties: the conventional solution of applying a coating of fluorocarbon resin and a novel solution based on nanostructuring. The latter creates a hydrophobic surface with a wide contact angle. As an alternative to these hydrophobic surfaces, a third variation was equipped with an active surface featuring both hydrophilic and photocatalytic properties. Another aspect of our investigations was the functionalization of textile-based building components to inhibit the formation of biofilms. We tested two different solutions, one of which focused on the use of various biocides, while the other used infrared-absorbing pigments or latent heat storage materials. In both cases, the aim was to inhibit microbial growth by significantly reducing the condensation caused by the overnight drop in temperature. A total of eleven different textile composite structures were tested in order to represent different combinations of the assessment criteria.
Tests and results
The functions of the various textile composite structures were tested not only in the laboratory using selected test methods but also in the open air at the outdoor test facility in Holzkirchen. Parallel to the functional tests in the laboratory, the characteristics of the materials incorporated into the textile composite structure were determined as the basis for mathematical simulations. The tests carried out at the outdoor test facility included a visual inspection and the use of measuring instruments to record temperature, relative humidity and heat flow at two different levels of the structure. To guarantee an objective assessment of the new textile composite materials, each of the eleven textile systems was directly compared with a conventional ETICS with an identical test setup being used for each pair of specimens. The extensive range of tests performed in the laboratory involved not only specimens in perfect condition but also, in some cases, specimens that had been exposed to different test stress scenarios (artificial weathering, abrasion tests, etc.).
The clearest way to present the results is in a radar chart, such as the two examples illustrated below. The first represents an unfinished textile system (T2) and the second a particularly promising textile system with an infrared (IR) pigment finish (T11), each compared with a mineral-based ETICS. Assessments awarded on a scale of 1 to 6 (1=excellent, 6=poor) for each criterion were derived from a thorough evaluation of the results from the various tests and simulations.
The test results obtained for Specimen T11 which has IR pigments incorporated into the textile system, are strikingly clear. Compared to the conventional mineral-based ETICS, this product exhibited distinctly superior properties in all criteria apart from its drying behavior, which was given the same rating. The relatively poor performance of the mineral-based thin-layer render system in terms of weather resistance is due to severe damage sustained by the top coat of render during a hailstorm in June 2007, a natural event that this otherwise weatherproof coating was unable to withstand.
The results of the detailed tests carried out in the laboratory and the outdoor test facility, supplemented by mathematical simulations, confirm that the new textile systems do indeed represent a viable alternative to conventional render systems. Moreover, the textile composite materials in the textile ETICS offer advantages that, for example, a state-of-the-art mineral-based render system is unable to provide. A case in point is the total absence of cracks in all textile systems tested in the outdoor facility. Two specimens have remained entirely free of microbial growth after more than three years of weather exposure. This is attributable to the significantly shorter cooling period below the dew point, and hence the smaller amount of condensation, as temperature measurements have shown. The tests carried out on the textile composite structures demonstrate the suitability of modified fabrics for use as external weatherproof cladding for façades. No noticeable defects were identified in the small-scale test specimens.
This research thus represents a milestone in the development of innovative, functional textile cladding systems. The numerous possible variations of the types of textile used open the door for many different applications as building components with an almost infinite combination of properties.