Application of a Bio-Based Coating for Wood as a Construction Material: Fire Retardancy and Impact on Performance Characteristics

The use of living micro-organisms as a protection method on surfaces of wooden building components becomes more common. Since wood is one of the relevant building materials to be used in a circular economy, fire safety and environmental issues are relevant aspects. Up to now, there is little experience in their potential contribution to fire-retardancy. This research aimed to get more information of a wood treatment with a so-called biofinish in combination with an ammonium phosphate based fire retardant. This biofinish system is comprised of a linseed oil impregnation and a protective and decorative coating based on the yeast-like fungus Aureobasidium [1]. Initial tests of wood treated with this biofinish and an ammonium phosphate based fire retardant showed positive effects on the fire growth rate index (FIGRA) and the heat release rate (HRR) in an European fire classification as well as in thermogravimetric analysis (TGA) assessments [2]. This is remarkable since linseed-oil is part of the coating formulation and used by the fungus as a nutrient. The behavior of samples treated with an ammonium phosphate based fire retardant and the biofinish was further studied in an one-year exposure test. This test revealed the potential esthetical stability of such a coating. The study resulted in crack formation and leaching of samples treated with ammonium phosphate and biofinish and stood in contrast with the behavior of wood samples treated with biofinish without an ammonium phosphate treatment.