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Decay patterns observed in butylene oxide modified ponderosa pine attacked by Fomitopsis pinicola
1983 - IRG/WP 1183
Small blocks of ponderosa pine chemically modified by butylene oxide to three different weight percent gains (WPG) were decayed for 2 months with the brown rot fungus Fomitopsis pinicola. Wood substance loss and the type of decay pattern recognised were fairly similar both for control and blocks treated to 8 and 15 WPG. No difference in attack was observed between radial or tangential walls in latewood tracheids. Microscopical examination of undecayed wood blocks treated to 23.7 WPG revealed numerous cracks in both the middle lamella regions of radial walls and in cell corners of latewood tracheids. The fungus had gained entry to the cracks, possibly via bordered pits and rays. Attack started from the cracks and progressed along the middle lamella and towards the cell lumen.
T Nilsson, R M Rowell

Artificial drying of impregnated wood
1987 - IRG/WP 3448
Sawn timber (Pinus Sylvestris) of dimension 50x150 mm was impregnated with CCA by a full-cell process. The timber was then dried in a conventional kiln or a special vacuum kiln where the timber was dried by circulating superheated steam. Drying time was 16 days and 2 days respectively. The aim of the investigation was to compare the physical appearence of the wood after drying by the two methods with particular reference to formation of checks. Moisture contents and checks were therefore recorded before and after drying. It was found that the number of checks formed was approximately the same by either drying system and no inner checks were found. The drying in superheated steam, however, caused bleeding of resin on the surface of the wood, which could be a disadvantage for some end uses.
M-L Edlund

Characterization of checks and cracks on the surface of weathered wood
2000 - IRG/WP 00-40153
The surface roughness of unweathered and untreated pine; unweathered copper chromium arsenate type C (CCA) - treated pine; weathered CCA-treated pine; and weathered CCA-plus-water-repellent (WR) - treated pine was evaluated by a stylus tracing method. Surface roughness parameters Ra, Rz, Rmax, Rk, Rpk, and Rvk were measured. Ra, Rpk, and Rvk were the most appropriate parameters for describing modifications on the wood surface. Ratios of the roughness parameters of the exposed (top) and unexposed (bottom) surfaces of the untreated, CCA-treated, and CCA + WR - treated wood samples were used to estimate the extent of the weathering damage on the exposed surface. The parameter ratios for the top and bottom surface were used to estimate the extent of the damage created by rain and sunlight on each piece of wood. This study shows that the stylus technique is appropriate to estimate the number and size of checks and cracks on wood surfaces after weathering.
D P Kamdem, Jun Zhang

Investigation of the suitability of silver fir (Abies alba Mill.) for thermal modification
2004 - IRG/WP 04-40275
In this study the suitability of silver fir (Abies alba Mill.) was examined for thermal modification. Comparative experimental investigations were performed with silver fir and Norway spruce (Picea abies Karst.) after thermal treatments. Besides properties, which characterize the quality of heat treatments, like dimensional stability and resistance against fungal attack, strength properties of the heat treated material were tested, i.e. bending strength, modulus of elasticity (MOE), impact bending strength and resistance to abrasion. Silver fir was found to be slightly more suitable for thermal modification than spruce, when treated at 180 °C, whereas thermal modification at 220°C showed a comparable suitability for both species. Advantages of silver fir were found for its impact bending strength, durability, and formation of cracks after weathering.
C Brischke, A O Rapp

Preliminary observations of the effect of growth ring orientation on the surface checking of flat sawn Southern pine decking
2005 - IRG/WP 05-20313
Checking in decking timber is a serious defect and methods of reducing its severity are required to ensure that wood can compete with alternative decking materials. The first aim of this research was to test the hypothesis that flat sawn Southern pine decking boards with growth rings oriented concave to the exposed surface will develop less severe checking when exposed outdoors than similarly exposed boards whose growth rings are oriented convex to the surface. A second aim was to examine the effects of wood type and three different types of fasteners on checking of boards. Five small decks were constructed each containing Southern pine decking boards with different growth ring orientations and manufactured from wood cut from close to the bark or nearer the centre of logs. Each decking board was fixed to the underlying sub-frame using 3 different types of fasteners, two of which were designed to permit flexural movement of the boards. The decks were exposed outdoors and after 6 months exposure the number and sizes of checks in the boards were assessed. Checks were significantly fewer in number and smaller in boards whose growth ring orientation was concave to the exposed upper surface than in boards whose growth rings were convex to the surface. There was no significant effect of wood type (inner or outer wood) and fastener type on the checking of boards. Orientation of flat sawn boards with growth rings concave to the exposed surface is a simple method of reducing checking of Southern pine decking boards. Further research is required to confirm these preliminary findings using preservative treated timber decking boards exposed for longer periods of time.
K Urban, P D Evans

Cantilever bending test of furfurylated poles
2008 - IRG/WP 08-40424
Ten, 8 m long poles of Scots pine (Pinus sylvestris) were treated with furfuryl alcohol to a WPG of approximately 40 %. A bending test was performed according to the principles in the draft European standard for wooden poles, prEN 14229 - Structural timber - Wood Poles for overhead lines. The bending strength and stiffness (MOE) for the poles tested were compared to an earlier study by the Swedish Wood Preservation Committee. In the latter study untreated, CCA-treated, ammoniacal Cu-PCP treated and creosoted poles were tested in bending. These types of poles were considered not to differ in strength and stiffness. The results of the furfurylated poles fit well with the results from the previous study. The bending strength and MOE values obtained are compared to the upper and lower 95-percentile values of the results from the previous study and all poles treated with furfuryl alcohol fit within this interval.Thus, this study indicates that a treatment with furfuryl alcohol does not result in a decrease of strength or stiffness. Further testing with a larger population of poles is necessary in order to get a statistically reliable result. In addition to further demonstration of the durability, the treatment process must be optimised to ensure full sapwood penetration and measures have to be taken to avoid the serious cracking observed in this trial before furfurylation can be considered for treatment of Pinus sylvestris poles.
R Ziethén, J Jermer, A Clang

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

Moisture distribution in glulam beams with natural cracks observed with CT Scanning before and after rain
2013 - IRG/WP 13-20534
The way cracks in outdoor wooden constructions affect durability is an interesting topic, since a certain amount of cracks can always be found naturally in wood and glued laminated wood. The question in this was, can cracks lead water into the wood and thereby increase the risk for decay and reduce strength and service life. Moisture balance, i.e., water absorption and water distribution were studied in two 2-meter-long glulam beams after exposure to rain. For the experiment, computer tomography and image processing were used. The beams were X-ray scanned on four occasions during one year: August (CT1), September (CT2), June (CT3) and the following August (CT4). One red-painted spruce beam 215 x 315 mm and one oiled pressure-treated pine beam 140 x 315 mm were studied. The study shows that water can enter a crack for many millimeters by capillary forces, but that this does not necessarily occur. How and to what extent water enters into a crack or delamination depends on material, surface treatment, position and size of the crack or delamination and the quantity of rain and wind. The sizes of the cracks depend on the climate, that is, moisture and temperature variation over time. Some of the cracks become invisible during this movement, and the variation can be as much as 2.5 mm over a 36-hour period. Under certain conditions, small cracks disappear as the woods swells.
K Sandberg

Acceptance levels of surface disfigurement - tolerance to defects of coated wood
2015 - IRG/WP 15-20564
Service life planning (PSL) has become an important issue in performance based building and substantial progress has been made in recent years. The role of predicting the aesthetical service life of wooden building components has been underestimated for quite long time but is recently attracting more and more notice. It is influenced by numerous factors such as discoloration, fading, flaking, cracking, and in extreme deformation due to interior rot. However, still the acceptance of such superficial disfigurement is subjected to the subjective sensation of consumers and end-users. This study aimed on evaluating different ‘technically defined’ limit states of weathered coated wood surfaces with respect to the acceptance of users. Therefore different groups of users were addressed in the frame of a survey as well as two different commodity groups were looked at separately, i.e. wooden window joinery and claddings. A remarkably high percentage of respondents ranked color and gloss related deficiencies as high as technical defects of the coating and recommended maintenance measures even when the coating was still fully intact. Technical characteristics such as the formation of cracks and flaking need to be considered separately from optical and aesthetical parameters for the definition of acceptance levels of coating disfigurements and defects. Limit states need to get defined specifically for different building components since acceptance varied significantly as shown exemplarily in this study between windows and cladding boards. For service life planning the overruling role of the subjective sensation of the user necessitates careful consideration.
C Brischke, P Kaudewitz

Evaluation of surface cracks on wood – physical assessment versus subjective sensation
2017 - IRG/WP 17-20617
In the presented studies from the University of Goettingen (Study I) and the University of Hannover (Study II), the assessment of cracks with different methods and their acceptance in general as well as depending on different target groups are investigated. The aim was to determine which factors are relevant for a crack evaluation and which visual impression of a wooden surface is tolerable for consumers. In both studies, the cracks were classified according to ISO 4628-4 (2004). In addition to the evaluation according to the standard, the specimens were evaluated in Study I according to a “school grade system”. The tolerance against cracks and discolouration on wooden surfaces was requested in study II during an interview survey at a DIY-market. The results showed that the number of cracks as criterion for the quality assessment was not decisive, but primarily the crack size. Cracks in claddings are more acceptable than cracks in decking. Furthermore, a uniform discolouration was more tolerated than a stained appearance of wooden surfaces. Both studies showed that the assessment of the quality of a wood surface is strongly dependent on the quality of the starting material. A wood surface with poor starting quality is generally less tolerated with regard to crack formation and discolouration. The estimation of the visual appearance of the test specimens according to a “school grade system” proved to be an adequate, complementary method for assessing the crack performance of wood.
A Gellerich, C Brischke, L Emmerich, L Meyer-Veltrup, P Kaudewitz

The influence of chemical compounds on wood cell wall to surface cracks
2020 - IRG/WP 20-40908
Degradation due to cracking and dimensional changes caused by drying, have a significantly negative impact on the preservation and durability of wood. Therefore, the prevention of surface cracking, which tends to occur during the drying process, is vital. High temperature set drying is one of the most effective methods for preventing wood surface cracking. It begins with softening the wood at a high temperature (100°C–120°C), allowing the surface to dry all at once, which deliberately forms a drying set. However, the mechanism by which wood surface cracks are prevented using the high temperature set method is yet unclear. In attempting to identify the said mechanism, this study focused on changes in the chemical components of the wood cell wall, particularly changes in hemicellulose, and discusses the hygrothermal (moisture and heat) impact on the chemical constituents of wood cell walls. There was no quantitative change to the cell wall’s chemical components due to hygrothermal treatment (HTT) at approximately 120°C. However, analysis of arabinoglucronoxylan (AGX) showed that its molecular weight was decreased significantly by the said treatment, indicating that the main chain structure of hemicellulose in the cell wall is significantly affected.
R Suzuki, Y Mori, K Yoshihiro, K Yamashita, M Kiguchi

Influence of weathering on surface roughness of thermally modified wood
2021 - IRG/WP 21-40915
Thermally modified wood is exposed to weathering similarly as other wood-based building materials. It has been reported that if thermally modified wood is exposed to weathering, its moisture performance might decrease fairly fast. The aim of this study was to determine whether this phenomenon is associated with crack formations or roughness. Norway spruce, thermally modified spruce, wax-treated thermally modified spruce, and European larch heartwood samples were exposed to artificial accelerated weathering and natural weathering for 9, 18, and 27 months. Samples were subsequently isolated and their roughness was determined with a confocal laser scanning microscope on axial and longitudinal surfaces at 10× and 50× magnification. After weathering, roughness increased on both axial and longitudinal surfaces. This was evident from the profile 2D measurements (Ra) and surface 3D measurements (Sa). The effect of natural weathering on roughness was higher than artificial accelerated weathering, presumably due to synergistic effects of abiotic and biotic factors.
E Kerzic, B Lesar, M Humar