SPRAYED POLYURETHANE ELASTOMER FOR THE LONGLASTING PROTECTION OF WOOD AGAINST WEATHERING
Due to the global demand for more sustainability in the construction industry, engineers and architects increasingly focus on the building material wood. Wood is very durable, as demonstrated by the old European timber-framed buildings and a renewable resource with an extremely low Global Warming Potential (GWP) compared to other materials. However the ecological footprint is getting worse if the material is used outdoors, because the weathering conditions can considerably reduce its durability. As a result the wood preservation has to be renewed regularly during its time of use. Common wood protection coating systems have to be renewed every 3 to 5 years, which is time consuming, costly and increases the ecological footprint of timber structures. The durability of wood which is protected by thin sheet metal is higher. However, this type of wood protection is expensive to produce and has a higher GWP. As an alternative to these two insufficient ways of wood preservation, a new thick-film polyurethane coating is proposed, which is sprayed on the surface of the wood. Currently, this procedure is still in trial stage, but first research results and practical applications are very promising. In comparison with conventional timber coating systems the durability of wood in outdoor applications is increased significantly and the maintenance cycles are substantially longer. These results indicate that thick-film PUR-coatings are well suited for an ecology-friendly wood protection system. A great advantage of the coating’s viscoelasticity is its ability to bridge cracks up to several millimetres. At the same time polyurethane is sufficiently permeable to water vapour. Currently the TU-Berlin carries out research in order to assess timber structures protected by spayed polyurethane elastomer and to gain expert knowledge about its durability.