Factors influencing mould growth and modeling of aesthetic service life: - coated and uncoated wooden cladding

Transcription

1 Factors influencing mould growth and modeling of aesthetic service life: - coated and uncoated wooden cladding Lone Ross Gobakken 1 and Olav A. Høibø 2 1 Norwegian Forest and Landscape Institute 2 Norwegian University of Life Sciences Background Blue stain fungi and moulds affect the aesthetic service life of wooden cladding façades Main requirements for fungal growth: moisture, temperature and nutrients (substrate) Several factors are influencing service life of wooden cladding façades Wood properties Craftsmanship Maintenance Design Wood moisture content and wood temperature Climate Type of wood protection 2 1

2 Objectives study selected factors that can influence growth of blue stain and surface mould on coated and uncoated wooden claddings address the importance and the possibilities of developing models that describe growth of blue stain and surface mould over time M & M 5 (6) field studies Sweden and Norway Combinations of wood substrates and coating typologies Recorded climate data Mould growth assessment Modelling Comparisons Simulations 2

3 Field study 1 Field study 2 Field study 3 Field study 4 5 modified wood substrates and 8 reference wood substrates 3 coating systems (WB + SB + SB/WB) Mould growth assessed 1 time a year for 4.5 years Field study 1 Field study 2 Field study 3 Field study 4 Norway spruce panels 6 model paints glossy, matt, soft, hard, hydrophopic and a film with pores (air inclusion) + commercial standard paint Exposed for 3 years assessed 11 times 3

4 Field study 1 Field study 2 Field study 3 Field study 4 7 wood substrates (including 3 modified substrates) 3 coating systems WB without fungicide, SB without fungicide and ICP + unpainted Exposed for 3 years assessed 11 times Field study 1 Field study 2 Field study 3 Field study 4 Norway spruce - low and high productive forest Manufacturing characteristic x 4 Wood properties x 5 1 coating systems - WB Exposed 3 years assessed 2 times per year 4

5 Field study 1 Field study 2 Field study 3 Field study 4 Field study 5 Acetylated SYP (three treatment levels) and untreated SYP Not coated Exposed facing south and north, September 2010 to March/May 2011 Mould assessment Assessment according to EN 927-3, 2000 and No mould growth Heavy mould growth The rating is based on a step-wise increase in mould growth coverage, but the shape and the pattern of the mould growth are also of importance to the determination (density and size) Mould rating using the standards makes the response variable ordinal 5

6 Statistical analysis and modelling Field study 1 proportional odds logistic regression model Mould rating a function of time, coating and wood substrate (species / sapwood-heartwood-mixed / modification or treatment type) Field study 2, 3 and 4 ordinal logistic regression model Mould rating - a function of time / coating typology / wood substrate / manufacturing characteristics / wood properties / relative humidity / temperature Results and discussion Several factors affects surface mould growth The factors have a synergetic effect, and to some extent it can be difficult to localise the most important contributing factor Coating Wood properties Wood substrate Exposure time Blue stain and surface mould Material climate t/rh/wmc Surface structure Climate micro/meso Manufacturing characteristics 6

7 Exposure time Exposure time had the greatest impact on fungal growth Surface mould growth adapt a sigmoid growth curve as a function of time The slope coefficient for mould coverage over time will decide the time when the panel will reach end of service life Every combination of wood substrate and type of surface finishes will have an unique growth curve. Wood coating Type of coating typology was, together with exposure time, the most significant factor for surface mould growth Clear differences in time of colonisation and speed in development of mould coverage between coating typologies 7

8 Wood substrates and wood properties Type of wood substrate was a less important factor than coating but still significant Copper treated wood, pine heartwood and larch heartwood had less mould growth than other substrates Thermally modified substrates resisted mould growth better than furfurylated and acetylated substrates Coated spruce claddings: wood properties and manufacturing characteristics had no significant effect on surface mould growth Effect concealed due to the use of a high performance coating system (?) Surface structure 5 Mould growth (0-5) Standard with fungicide Soft Matt Air inclusion Hydrophob Glossy Hard Standard without fungicide Surface structure (type of model paint) had significant effect on mould growth Hard and glossy model paint was most susceptible to mould growth 8

9 Relative humidity, temperature and cardinal direction RH, precipitation and temperature were tested in initial models to try to capture the effects of the local climate RH and temperature were found significant and kept in a final model Simulations made over a wide range in RH and temperature indicated that a general increase will give more mould growth Cardinal direction had a clear effect on mould growth but the effect can vary due to type of test material, test set-up and location. Mould rating Acetylated southern yellow pine three treatment levels uncoated exposed 9 months Norway spruce claddings coated and uncoated exposed 1,5 years 9

10 Current work. Material climate wood moisture content wood temperature Ambient air RH and temperature 10 mm in front of the panels Colour of the surface Open / shadowed environment Studies of user preferences aesthetic service life need for maintenance Conclusions Developing models for mould growth allow investigation of specific effects contributing to the variation in surface mould growth development over time Exposure time and type of surface finishing affect surface mould growth the most The individual mould growth curve and slope coefficient decide when a specific combination of wood substrate and surface finish reaches maximum mould rating and end of aesthetic service life Statistical models can be used to study the effects of climate change on deterioration and service life of exterior wooden claddings 10

11 Acknowledgement: Mats Westin SP Technical Research Institute of Sweden Patricia Lebow USDA Forest Service - Forest Products Laboratory, Madison, USA Halvor Solheim Norwegian Forest and Landscape Institute Geir I. Vestøl Norwegian University of Life Sciences Stig Bardage SP Technical Research Institute of Sweden Mari S. Sivertsen Mycoteam as Thank you for your attention! Photo: Oskar Puschmann, Photo: Skog Oskar og Puschmann landskap Skog og landska 11