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Some practical implications from recent research on the fixation of CCA preservatives
1975 - IRG/WP 358
The mechanism of fixation of CCA preservatives is briefly described. If the temperature is increased during the primary fixation period, the formation of intermediate fixation compounds is less extensive. The length of the primary fixation period is of practical interest. It is determined by preservative composition and concentration, temperature and wood species. Diagrams are given for Pinus sylvestris. Light exposure and drying during the primary fixation period cause variability in colour intensity of CCA treated wood. Disproportionation of preservative elements with penetration depth is explained by the fixation mechanism. Conversion of intermediate fixation compounds into stable ones occurs even below the fibre saturation point, as long as the moisture ratio is sufficiently high to allow ion transport. Conversion reactions are very slow. A correlation was found between the final pH of treated timber and leachability in fresh water of copper and arsenic. The final pH depends on preservative composition and concentration, wood species and to some degree of drying and storage conditions. An electrolyte such as sodium sulfate does not affect the leachability. In saline waters leachability is increased by complex formation of Cu(II) and Cr(III) with chloride and hydroxide and the salt effect on activity coefficients. The leaching of arsenic is delayed.
S-E Dahlgren

Preference of swarming termites for various colored lights
1984 - IRG/WP 1238
The ability of the alates of the drywood termite Bifiditermes beesoni (Gardner) to discriminate ten different colored lights was studied. When an alternative choice of any of two colors was offered, the light-blue was preferred to all other tested colors by 97.7% of the alates. A lower degree of attractivity was found for some other colors and certain other colors were indistinguishable. Furthermore, the effects of light intensity and preconditioning to certain colors have been studied and finally the response of swarming alates from natural colonies is compared to that of the individuals from laboratory colonies.
M Afzal

Heat treatment of less-valuable Nigerian-grown Ceiba pentandra wood for improved properties
2006 - IRG/WP 06-40332
The hardwood Ceiba pentandra locally known as “ araba “ in Nigeria is rarely used for structural and construction works due to its high dimensional instability, low strength and durability values. Samples (10 x 10 x 150mm) were removed from four green boards (25 x 200 x 3000mm) of this species originating from a natural forest stand in Nigeria and subjected to 2-hour heat treatment at 160°C and 220°C. Heat treatment reduced swelling, hygroscopicity and swelling intensity of Ceiba pentandra wood with the reductions being generally higher in the 220°C treatment than the 160°C treatment. The reductions constitute improvements in these properties. These improvement in properties have the potential to increase the market value of this species through wider acceptability for various purposes hitherto considered impossible. This however is subject to further investigations on the effects on durability and strength properties which are other key features in the choice of wood for various purposes.
L Awoyemi

Safer alternative reagents for colour differentiation of heartwood and sapwood
1994 - IRG/WP 94-20028
Benzidine and dimethyl yellow reagents have been used for distinguishing heartwood from sapwood in the Pinaceae and Araucariacae families, and in Eucalypt species. Both have been classified as carcinogenic by European and United States authoritites, yet the need for effective heartwood/sapwood differentiation remains, not only in the laboratory but also out in the timber processing chain. Safer alternative reagents have been proposed over the past twenty years, but some of these have since been linked with health problems, and most of the rest lack the specificity and general usefulness of those traditionally used. Recent research has investigated various azo, diazo, and other nitrated reagents. Safe but useful alternative methods of sapwood/heartwood differentiation are being established, and recommendations are made for several timber species.
A Zosars, M J Kennedy

Acceleration of the fixation of chromated wood preservatives by UV-radiation
1989 - IRG/WP 3544
Preliminary laboratory tests demonstrated that the fixation of chromated water-borne wood preservatives may be accelerated by UV-radiation. The degree of fixation depends on the intensity of radiation and the prevailing temperature. Three hours radiation at 20°C in a device for artificial weathering diminished the leaching of chromium to 43% and of copper to 23% compared to not-radiated samples. Two hours radiation at 60°C gave almost complete fixation. Five to seven seconds radiation in a high energetic commercial plant for hardening of paints diminished the leaching of chromium to 75% and of copper to 30% and a second radiation of the same samples still increased the fixation. Further tests are necessary to obtain more details on the use of UV-radiation for fixation in practice.
H M Illner, H Willeitner, K Brandt

Towards a colour assay of wood degradation
1982 - IRG/WP 2180
A colour assay for the enzyme catalase is described. Since the activity of this enzyme has previously been shown to be correlated with degree of wood degradation as determined by other methods, this assay may provide a rapid quantitative indicator of superficial and internal wood decay.
M A Line

Correlation between changes in colour and chemical composition during photo-degradation of wood surfaces
2005 - IRG/WP 05-40301
Changes in colour of wood (yellowing) during photo degradation or weathering reflect chemical changes in wood. Therefore, the relationship between changes in chemical composition and CIELAB colour parameters is very important to characterize photodegradation of lignocellulosic surfaces. In this study, the changes in chemical composition and yellowing due to photo-degradation was studied by exposing wood surfaces of Pinus roxburghii (chir pine) to a xenon source. Changes in chemical composition were monitored by measuring IR and fluorescence spectra and were correlated with colour changes. A linear correlation between degradation of lignin and total colour change (E) was observed.
K K Pandey

On the Influence of Wood Destroying Fungi on the Feeding Intensity of Termites
2017 - IRG/WP 17-10893
The baiting and feeding stimulating effect of wood attacked by fungal isolates of the species Coniophora, Lentinus, Poria and Gloeophyllum on termites Reticulitermes santonensis is examined. There are significant relationships between the activity of fungal isolates and the feeding behaviour of termites. The most active isolates can be used for increase the attractiveness of wood to wood-destroying termites.
W Unger, T L Woods

Observations on the morphology, ecology and biology of Xylophaga dorsalis (Turton) (Mollusca: Xylophagainae) in the Trondheimsfjord (Western Norway)
1981 - IRG/WP 475
The paper deals with various aspects of the systematics, ecology and biology of the little known pholad wood-borer, Xylophaga dorsalis (Turton) of the Trondheimsfjord (Western Norway). Diagnostic characters of the species have been given based on examination of fresh living specimens and accommodating the several morphological variations. A key to the identification of Norwegian species of Xylophaga is also included.
L N Santhakumaran

Effects of wood-inhabiting marine fungi on food selection, feeding intensity and reproduction of Limnoria tripunctata Menzies (Crustacea, Isop.)
1981 - IRG/WP 480
The paper gives a condensed survey on laboratory tests with Limnoria tripunctata Menzies and pure cultures of 9 different marine wood-inhabiting fungi. Limnoria is able to distinguish between fungus-infested and non-infested wood. Wood with dead mycelium mostly proved to be less attractive or even repellent and was initially consumed less than with living fungi. On non-infested wood, initial feeding is retarded by 2 to 4 days. On fungus-infested wood less eggs degenerated and the number of reproductives was higher than on non-infested wood. Humicola alopallonella-infested wood yielded the highest number of reproductives. But the attractiveness of a fungus, the feeding stimulus produced by it and its nutritional value often did not correspond. It was not possible to make generally valid conclusions for one fungus species.
H Geyer

Observations on the morphology, ecology and biology of Xylophaga dorsalis (Turton) (Mollusca: Xylophagainae) in the Trondheimsfjord (Western Norway)
1981 - IRG/WP 466
The paper deals with the various aspects of the systematics, ecology and biology of the little known pholad wood-borer, Xyophaga dorsalis (Turton) of the Trondheimsfjord (Western Norway). Diagnostic characters of the species have been given, based on examination of fresh living specimens and accomodating the several morphological variations. A key to the identification of Norwegian species of Xylophaga is also included. Seasonal intensity of the species, based on incidence on a number of pine wood panels, exposed for overlapping periods for 1 year has been analysed. In shallow waters, larval settlement is restricted to summer and ear1y autumn, whereas at greater depths, the same extends even during the winter and spring. Inhibitive action of fouling organisms on the settlement of Xylophaga dorsalis has been indicated. Vertical distribution of the species at every 3 m from intertidal level to 30 m, and also at depths of 40 m, 70 m, and 100 m has been described. Intensity of attack increases with depth with maximum concentration near the mud-line. The borer prefers the silted upper surface of the panel for settlement than its lower surface and sides. Growth-rate of the borer has been studied based on burrow length measurements as well as on length and height of the shell valves. Boring activity is extremely rapid in the Trondheimsfjord, maximum length of burrow being 58.50 mm attained in less than 8 months. Data on growth-rate at different levels show that the length and height of the shell valves increase gradually as the depth increases, and larger individuals are always metwith in deeper levels. Burrow length measurements also indicated the same trend except close to the mud-line where the size declined possibly due to overcrowding. Distribution of specimens of various length classes at different depths also followed the same pattern with individuals belonging to larger size groups being predominant at deeper levels. Length and height of the shell valves, length of burrow and distribution of specimens of various size groups at 40 m, 70 m, and 100 m depths also demonstrated a similar trend. Preliminary observation on salinity tolerance indicates that the borer is very sensitive to decrease in salinity, and below 18.77% they are unable to survive for more than 24 hours. Incidence of Xylophaga dorsalis on various timber species illustrated that the borer is capable of attacking all timber species, although in a few the larvae do not succeed beyond making tiny pits. The results are briefly compared at appropriate places with those of earlier workers.
L N Santhakumaran

High-energy multiple impact (HEMI)-test – Part 2: A mechanical test for the detection of fungal decay
2006 - IRG/WP 06-20339
The suitability of the high-energy multiple impact (HEMI)-test for detection of early fungal decay was examined. The HEMI – test characterizes the treatment quality of thermally modified wood by stressing the treated material by thousands of impacts of pounding steel balls. This method differentiates between heat treatment intensities, which are expressed by structural changes of the wood. Similar changes of the wood structure are known for wood decayed by fungi. Pine (Pinus sylvestris L.) decayed by brown rot and beech (Fagus sylvatica L.) decayed by white rot were tested. Mass loss caused by fungal decay and the resistance to impact milling (RIM) determined in HEMI-tests were found to be highly correlated. Testing of non-degraded pine, beech, and ash (Fraxinus excelsior L.) showed only marginal effects of wood density on RIM. Furthermore, annual ring angles and RIM of spruce (Picea abies Karst.) were found to be not correlated. Accordingly, the detection of strength reduction of decayed wood is not masked by variations in density and orientation of the annual rings. Previous results showed no adverse effects of weathering on RIM. Thus, the detection of fungal decay with HEMI-tests is feasible, not only for laboratory purposes, but also for wood in outdoor applications, which was already weathered.
C R Welzbacher, C Brischke, A O Rapp

High-energy multiple impact (HEMI)-test – Part 1: A new tool for quality control of thermally modified timber
2006 - IRG/WP 06-20346
Thermal modification processes improve durability and dimensional stability of wood, but the strength properties, especially the dynamic ones, are compromised and need to be considered with respect to industrial quality control. Results from standard dynamic strength testing, such as impact bending tests, suffer from high variability, and therefore require a high number of replicates. To overcome this, a new test method named high-energy multiple impact (HEMI) was developed. In the present paper heat treated beech (Fagus sylvatica L.), spruce (Picea abies Karst.), silver fir (Abies alba Mill.), and larch (Larix decidua Mill.) were investigated. The HEMI method is based on crushing small specimens by thousands of impacts of pounding steel balls in a heavy vibratory mill. The level of destruction was determined by slit sieving and analysing the size distribution of the fragments. We calculated the resistance to impact milling (RIM) based on the mass of the size fractions. RIM showed a linear correlation with the decrease in mass of the wood by the thermal treatment. The HEMI-test method has the following advantages: small number of specimens, short time for specimen preparation, small variances, high reproducibility of the results, and applicability to timber out of service for a subsequent quality control.
C Brischke, A O Rapp, C R Welzbacher

The Effect of Flavonoids on Colour and Spectral Changes of the Wood Surface Caused by Heat Treatment or Ultra-violet Irradiation
2006 - IRG/WP 06-40341
Both heat treatment and UV irradiation can cause discolouration and change in the spectral properties of wood surface. Some of the characteristic flavonols have significant role on colour and spectral changes, despite of their relative small quantities in wood. Colour changes and spectral properties of natural and extracted black locust (Robinia pseudoacacia L.) and poplar (Populus nigra L.) were investigated by CIELAB colour measurement system, FTIR and UV/Vis spectrophotometry. Spectral properties of representative flavonols, impregnated on inert silica gel thin layer, were studied in addition to the two types of wood samples. Chemical structure of flavonols was established to have both influence on the colour and spectral changes of woods and close connection with their thermal and photo stability. A slow but continuous decrease of lightness was observed in the case of quercetin and its homologous compounds. Chemical reaction of robinetin was detected by thermal analysis and differential scanning calorimetry under 200 °C and both oxidative and inert conditions. The colour changes of quercetin homolog compounds, kaempferol and fisetin, which contain one and two hydroxyl group on their “B” ring, are similar to quercetin; while myricetin with three hydroxyl groups on its “B” ring shows “robinetin-type” changes. The colour changes of the hardwoods are depended on the time and temperature of heating, as well as on the time of light irradiation. The character of spectral changes of black locust can be classified on the type of robinetin, in contrast with the “quercetin-type” of poplar.
R Csonka-Rákosa, L Molnár-Hamvas, E Börcsök, J Molnár, K Németh

Photo-degradation of modified and non-modified wood, coated with water borne acrylic coatings during artificial light exposure
2007 - IRG/WP 07-30416
A series of experiments were carried out to investigate photo-degradation of thermally modified (at 210oC and – 0.9 bars for two hours) and non-modified spruce wood (Picea abies L (Karst)), coated with transparent and semitransparent (with 3% pigment content) acrylic coatings during artificial UV light irradiation for 200 hours. Photo-degradation was evaluated in terms of colour changes throughout the irradiation period at an interval of 50 hours, along with IR and EPR spectroscopic study. One set of modified and non-modified woods was painted with coatings, while the other set was covered with free films made of coatings, just to simulate coated wood. The average thickness of paint-coats and dried free films at 25oC and 50% RH was 144.8?m and 143.4?m for transparent and semitransparent coating, respectively. The colour changes for both modified and non-modified wood samples without paint-coat and free film cover were comparable to that of wood samples with paint-coat and free film cover for transparent coat type, which indicated its ineffectiveness to prevent photo-degradation of wood underneath. However, the colour changes for both modified and non-modified wood samples with paint-coat and free film cover were much more lower than that of samples without paint-coat and free film cover for semitransparent coat type, which might be due to hindrance of transmission of light energy through pigment to reach the underlying wood surface. On the other hand, whole substrate-coating systems showed better photo-stability, when thermally modified wood was used as substrate. It might be due to increase in lignin stability by condensation during thermal modification process of wood substrate. However, the colour changes of coat-painted and free-film covered samples for both modified and non modified woods might be due to due colour changes of wood specimen underneath, because free films of both the coat types showed negligible colour change during UV irradiation.
M Deka, M Tomažic, M Petric

Effectos de la intemperización artificial sobre la madera de mezquite (Prosopis laevigata)
2008 - IRG/WP 08-40430
The effects of artificial weathering on Prosopis laevigata wood were studied on eight replicates (150 x 72 x 15mm (l x t x r)) free of knots, cracks and resin. The samples were exposed tangentially to UV light and to water spray during three cycles (1 cycle corresponded 1 week of artificial weathering). The conditioning time between each cycle was thirty days. The effects were measured according to visual appearance, crack formation, and colour changes; the results were then compared to two other well known timber species, namely teak (Tectona grandis) and beech (Fagus sylvatica). The specimens displayed changes in colour after three cycles of exposure. P. laevigata changed from brown to white. Delta C (Delta colour) increased from 5.6 to 9.6. There was less crack formation than in F. sylvatica but more than in T. grandis. Lightness was reduced from 61 to 37 after the first cycle; the lightness value of 35 was maintained at the end of the second and third cycles. The P. laevigata specimens showed several changes in colour after artificial weathering. The Delta C was higher due to the photodegradation of lignin and phenolic compounds caused the UV light and the leaching caused by water.
A Carrillo-Parra, F Hapla, C Mai

Mechanical and chemical properties of blue stained wood
2009 - IRG/WP 09-10686
Discoloration of wood is frequently caused by blue-staining fungi. In the previous researches there was general opinion that blue-stain fungi do not influence mechanical properties. On the other hand, there were some opposite results reported as well. In order to elucidate this issue, specimens made of Pinus sylvestris sapwood were exposed to two the most frequent and important blue stain fungi Aureobasidium pullulans and Sclerophoma pithyophila for various periods between two and eight weeks. Before and after exposure, FTIR, weight, colour and modulus of elasticity measurements were performed. The data obtained showed, that blue stain fungi besides considerable discoloration, does not cause any significant damage to wood. Surprisingly the non-destructive MoE analysis showed, that modulus of elasticity even slightly increase after the experimental exposure.
M Humar, V Vek, B Bučar

Colour change monitoring of photodegradation in Scots pine (Pinus sylvestris) – a short term focus
2009 - IRG/WP 09-40442
Colour change monitoring of photodegradation is a quick and easy method for monitoring rates of photodegradation in timber. A study was undertaken to compare this technique to other monitoring methods, including microtensile strength changes and weight loss. Colour changes due to accelerated sunlight exposure were monitored using a Datacolor check spectrophotometer and compared with a set of controls. Measurements on both samples and controls were performed hourly for the 1st 24 hours and there after daily until 168 hours’ exposure with extra measurements at 200, 350 and 500 hours. A subset of samples, were extracted prior to exposure to check the effects of any colour change due to the presence of extractives. Data was analysed using the reflectance spectra (400-700nm) as well as the CIE-L*a*b* system and ΔE. The majority of colour changes were found to occur within the 1st 24 hours. This was unaffected by the removal of extractives from the wood and was independent of temperature. When compared to the other monitoring methods, colour monitoring has been shown to be the most sensitive method out of the methods compared for monitoring photodegradation in Scots pine.
V Sharratt, C A S Hill, D P R Kint

Estimating the heat treatment intensity through various properties of thermally modified timber (TMT)
2009 - IRG/WP 09-40459
The suitability of different measures for prediction of the heat treatment intensity was investigated. Therefore, the resistance to impact milling (RIM), the lightness L*, the equilibrium moisture content (EMC), the anti swelling efficiency (ASE) and the total amount of soluble carbohydrates (TSC) of heat treated specimens were correlated with corresponding fungal resistance achieved by heat treatments. Heat treatment temperatures of 180°C, 200°C, 210°C, 220°C, and 240°C for various heat treatment durations from 0.25 to 72 h were applied. The results show, that the decrease in mass (dm) by heat treatments is a suitable measurand to describe the treatment intensity, which is a product out of treatment temperature and duration, where the impact of temperature is predominating the impact of time. The properties examined showed a strong reciprocally proportional relationship with the decrease in mass. Thus different correlations were found for the various treatment temperatures: The higher the temperature applied, the lower was the decrease in mass required for an equivalent improvement of certain wood properties, e.g. biological durability, EMC, and dimensional stability. However, mass loss by Poria placenta correlated well with the resistance to impact milling (RIM), lightness L*, EMC, ASE and TSC of the different heat treated specimens, depending on the heat treatment temperature. Consequently, a reliable estimation of improved fungal resistance of TMT, as well as the quality control of TMT in general, strongly requires certain process information.
C R Welzbacher, C Brischke, A O Rapp

Development of markers to predict decay durability of heat treated wood
2010 - IRG/WP 10-40496
Effect of heat treatment temperature on elemental composition of Scots pine sapwood (Pinus sylvestris) has been investigated in the range of temperatures between 220 and 250°C. Results revealed an important increase of carbon content, while oxygen content significantly decreases. Independently of the heat treatment temperature, elemental composition is strongly correlated with the mass losses due to thermal degradations. Carbons content as well as O/C ratio seem to represent valuable markers to estimate wood degradation after heat treatment. Heat treated specimens were exposed to fungal decay using the brown rot fungus Poria placenta and the weight losses due to fungal degradation were determined. Correlations between weight losses recorded after fungal exposure and elemental composition indicated that carbon content or O/C ratio can be used to predict wood durability conferred by heat treatment allowing to envisage the development of a proper method to evaluate the quality of heat treated wood and predict its durability. These results also confirm that chemical modifications of wood cell wall polymers are the main factors responsible for wood durability improvement against fungal decay after heat treatment.
Ž Šušteršic, A Mohareb, M Chaouch, M Pétrissans, M Petric, P Gérardin

Comparison of colour change in wood clear-coating systems including inorganic and organic UV absorbers for exterior use
2010 - IRG/WP 10-40499
The aim of this work is to compare the performance of inorganic and organic UV absorbers used in a wood coating application against weathering. Our study has investigated the colour changes of selected UV absorbers; hombitec 402 RM from the Sachtleben Company as an inorganic UV absorber, tinuvin 477 DW from the Ciba Company as an organic UV absorber. The study was carried out on two wood species; Fagus sylvatica L., Pinus sylvestris L. The results obtained after 28 days (672h) of accelerated weathering showed that the colour stability was the same for hombitec 402 RM and tinuvin 477 DW and both systems showed a significant improvement of colour stabilization compared to the control samples. In addition, the wood surface from cracks was protected with the clear-coat containing both of UV absorber.
Ö Özgenç, B Forsthuber, A Teischinger, C Hansmann

TMT–Interlab–Test to establish suitable quality control techniques - Structure and first results
2010 - IRG/WP 10-40503
As a result of growing quality demands from manufacturers and end-consumers of thermally modified timber (TMT) recent scientific research activities are increasingly focussed on modification mechanisms and by this on the development of suitable quality control methods. To deepen the knowledge in modification mechanisms and to obtain a larger variety of scientific data for TMT depending on the treatment intensity, a worldwide interlaboratory test series with TMT was started with nine research institutions involved, each contributing with their own most appropriate techniques and experiences. Therefore European beech and Norway spruce were thermally modified with different treatment intensities at Leibniz University Hannover and allocated to the involved partners. Basic treatment and material characteristics of the TMT used in the tests are presented in this paper and show that the decrease in mass by thermal modification (dm) is a suitable measure to describe the treatment intensity both for beech and spruce. Furthermore, color values and static mechanical strength properties proved to be highly correlated with dm. Consequently a strength prediction of TMT by color values appears applicable. Furthermore, correlations of dm with other target properties and further indicator measures are promising.
C R Welzbacher

Performance of selected types of coated and uncoated modified wood in artificial and natural weathering
2010 - IRG/WP 10-40510
The objective of the present work was to investigate the influence of commercial wood modification methods on weathering behaviour and coating performance. It was aimed to compare modification methods and to set up maps of weathering behaviour for these methods with and without a semi-transparent wood stain. Artificial and natural weathering trials were carried out with a selection of different types of modified wood. Unmodified pine sapwood was used as reference. Acetylated radiata pine wood revealed outstanding performance in colour stability and as coating substrate in all weathering trials. The performance of thermally modified pine sapwood was comparable to the unmodified reference. Its colour change was characterised by bleaching of the original dark colour. Uncoated furfurylated pine sapwood samples showed strong colour change with extensive bleaching, whereas coated furfurylated wood showed good colour stability. Coated Cr-free impregnated pine sapwood showed sensitivity to mechanical defects of the semi-transparent coating film, leading to strong discolouration. These results indicate the possible influence of preservative impregnation on coating performance of semi-transparent stains.
G Grüll, L Podgorski, M Truskaller, I Spitaler, V Georges, S Bollmus, A Steitz

A comparative study and evaluation of methodologies used for determining wood preservative penetration
2011 - IRG/WP 11-20475
A series of methods for determining penetration of wood preservatives into the wood structure have been developed for either quality control (QC) or research and development purposes. QC methods range from monitoring the solution uptake, applying colour indicators or sampling specific wood samples followed by wood acid digestion/atomic absorption spectroscopy (AAS) or solvent extraction/chromatography analysis. Several standard methods for penetration analysis were developed by various standardization groups (e.g. AWPA, CEN). They are mostly used in correlation with a specific wood preservative system. Additional analytical tools are necessary for detailed penetration studies, especially during product development of a new wood preservative. Sufficient penetration of the active components into the wood structure plays an essential role in determining the service life of treated wood. Depending on the desired end use (use class) of the treated wood component, different penetration requirements apply. Therefore studying and optimizing the penetration characteristics of new wood preservatives must be an integral part during their development. Furthermore monitoring that the penetration requirements are fulfilled in the wood treatment process is an important aspect to ensure the quality of treated wood products. The aim of this study was to review several methods currently employed to determine the penetration of the wood preservative actives e.g. colour indicators, solution uptake of treated wood, direct gradient studies by wood acid digestion/atomic absorption spectroscopy or solvent extraction/chromatography analysis, and microbiological studies using different types of fungi. Factors which can impact on the outcome from these methods are being discussed based on some “model” wood preservative systems.
R Craciun, R Moeller, J Wittenzellner, T Jakob, J Habicht

Effects of microclimate, wood temperature and surface colour on fungal disfigurement on wooden claddings
2012 - IRG/WP 12-20490
Wooden claddings are common in façades in Norway, and Norway spruce (Picea abies) is the most frequently used species. The cladding is a major part of the facade, and it has visual requirements that may define the aesthetic service life. The visual changes that occur during weathering can be colour changes, abrasion or wear, blistering, flaking, and even cracks in the wood or coating, but more often growth of mould and blue stain fungi are the main challenge. A field test with synchronous monitoring of relative humidity, air temperature, material temperature and wood moisture content in Norway spruce claddings has been established in southern Norway as part of the ClimateLife project. Visual evaluation of blue stain and mould growth according to EN 927-3 was performed, and evaluation data after 10 months exposure is presented. The objectives were to study the effect of 1) environment, 2) cardinal direction and 3) colour of the cladding on growth of blue stain and mould fungi, and further study the variation in relative humidity, air temperature in front of a surface and the material temperature due to change in 1) environment, 2) cardinal direction and 3) colour of the cladding. After 10 months exposure, the red coating system had lowest mould ratings and the uncoated claddings had the highest. Claddings facing south tend to have higher mould ratings than those facing north. No difference was found between shaded and open environment. The relative humidity was higher in front of the claddings exposed in a shaded environment compared to an open environment, and in an open environment the relative humidity was lower against south than north. The temperature in front of the red coloured claddings was highest. Except for the red-coated claddings, the air temperature was higher than the material temperature.
L Ross Gobakken, G I Vestøl

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