IRG Documents Database and Compendium

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The possible role of mobile CCA components in preventing spore germination in checked surfaces, in treated wood exposed above ground
2001 - IRG/WP 01-30263
Untreated check surfaces are often exposed in CCA-treated lumber of refractory species used above ground since, during weathering, some checks develop beyond the preservative penetrated zone. However, decay is seldom observed in these checks even after many years of exposure. It is hypothesized that minor amounts of mobile CCA preservative components redistribute during weathering into checks, and that this 'surface treatment' prevents fungal spores washed into checks from germinating and causing decay. A substantial amount of copper was found on the exposed check and end-cut surface in exposed wood through the current research, and whether spores are prevented from germinating by this amount of chemical is being studied.
S Choi, J N R Ruddick, P I Morris

Quality of timber impregnated with preservatives of class AB after three years in service
2002 - IRG/WP 02-20241
Quality of impregnated timber is most often expressed by penetration and retention of the preservative used. Relatively less information is available about the performance of the final product, e.g. decks, panels etc. regarding product’s surface checks, deformations and overall appearance. Together with the timber durability, the above mention features are of esthetical importance in the above ground performance of timber. A comprehensive Nordic project dealing with pre-treatment, impregnation, durability and performance of Scots pine timber impregnated with copper-based preservatives for above ground use (class AB) was recently finished. The results from an above ground trail concerning the quality of timber are presented. The timber was dried in a conventional progressive, batch and high temperature kiln prior to impregnation. A significantly better quality regarding checks, deformations and deviation of the final moisture content, was achieved after conventional batch and high temperature dryings. Three preservatives (Kemwood ACQ 1900, Tanalith E and Wolmanit CX-8) were impregnated. The high temperature drying ensured the best penetration of all preservatives, but the retention was lower compared to conventional progressive and batch kiln dried timber. A part of the planks were conventionally kiln dried after the impregnation, the second part was air dried. Two decks with planks covering the variations in primary drying and preservative used were exposed; the former deck was in the open, the later one was under a shelter. After three years in service the planks were assessed regarding checks, deformations and moisture content. All three preservatives showed satisfactory appearance and no indication of decay was found. The deformations were comparable to those measured directly after final drying; the type of exposure had effect on the checks and moisture content of timber.
N Terziev

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

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

Preliminary Observations of the Effect of Kerfing on the Surface Checking and Warping of Flat Sawn Southern Pine Decking
2007 - IRG/WP 07-20360
Checking and warping of decking timber are serious defects and methods of reducing their severity are required to ensure that wooden decking can compete with alternative decking materials. Kerfing is effective at reducing the checking and distortion of square cross-section lumber, and the checking of roundwood. In the past it has also been applied to preservative treated decking boards, however, there is no information on whether kerfing reduces the surface checking or warping of treated boards. In this study one, two or three kerfs were sawn to depths of 10, 13, or 20 mm into the underside of 140 mm (width) x 40 mm (thick) southern pine decking boards. Kerfed boards and matched unkerfed controls were exposed to natural weathering for 1 year and the surface checking and distortion of boards was measured. The aim was to determine whether sub-surface kerfing of decking boards could reduce the surface checking and distortion of boards, and the kerfing treatment (kerf number by depth) that was most effective at reducing both the checking and distortion of boards. Kerfing reduced the cupping of boards exposed to the weather, but had no significant effect on twist, or bow. Both the single and triple kerfs were effective at reducing the cupping, whereas the double kerfs were ineffective. There was a positive correlation between kerf depth and reduction in cupping, and the kerf sawn to a depth of 20 mm was particularly effective at reducing cupping. Kerfing had no statistically significant effect (p>0.05) on the surface checking of boards, although in most cases checking of boards containing kerfs was greater than that occurring in the unkerfed controls. Further research is needed to confirm these preliminary findings.
R Ratu, J Weizenegger, P Evans

Mobility of Copper from MCQ in Shell-Treated Wood Exposed Above Ground
2010 - IRG/WP 10-30534
Most Canadian treated decking in service has been given just a thin shell of preservative treatment but it has still performed very well. This is because copper migrated into checks and prevented germination of basidiospores on the freshly exposed untreated wood. Unlike soluble copper systems, MCQ has its copper primarily in the form of small basic copper carbonate particles. For MCQ to be effective as a shell treatment, some of this copper will need to be mobile. A field exposure test was initiated and monitored for one year. Significant amounts of copper were detected in all leachates from MCQ-treated wood. The copper leaching from MCQ-treated wood was low but steady rather than the early flush and decline in loss typical of ACQ- treated wood. Check analysis revealed copper concentrations of 0.18 mg/g and 0.99 mg/g after five months and one year, respectively. After one year of exposure the amount of copper detected in the checks greatly exceeded the 0.27 mg/g previously reported to prevent the germination of basidiospores.
R Stirling, P I Morris

Quantitative design guideline for wood outdoors above ground applications
2011 - IRG/WP 11-20465
This paper describes the background and principles behind an engineering design guideline for wood in outdoor above ground applications, i.e. use class 3 according to EN 335. The guideline has been developed in the European research project WoodExter and can be seen as a first prototype for a quantitative design tool in the area of wood durability. It is based on a defined limit state for onset of decay under a reference service life of 30 years. Onset of decay is defined as a state of fungal attack according to rating 1 in EN 252. The approach is to determine the climate exposure as a function of geographical location, local exposure conditions, sheltering, ground distance and detail solution. The exposure is then compared with the material resistance defined in five classes and the design output is either OK or NOT OK. The present version of the guideline covers applications for decking and cladding. The data included in the guideline have partly been estimated with the help of a dose-response model for decay, which was used here to derive relative measures of decay risk between different locations and between different detail solutions. Some other elements have however been estimated in a semi-subjective manner based on expert opinions as well as experience from field testing. The guideline has been verified by a number of reality checks, which show that the output from the tool agrees reasonably well with documented experience. The guideline has also been presented in a computerized Excel format, which makes practical use convenient. It is believed that many building professionals will appreciate a tool within the area of wood durability which has an approach similar to other design tasks in building projects. An advantage is that in applying the method the designer will go through a check list where he/she becomes aware of the importance of appropriate detailing solutions. In addition the user will have to think about the target service life as well as the consequences of non-performance in the design of a construction.
S Thelandersson, T Isaksson, E Suttie, E Frühwald, T Toratti, G Grüll, H Viitanen, J Jermer

Evaluation effect of kiln schedule on Warp, Twist, Bow and surface checks in Poplar Wood
2011 - IRG/WP 11-40565
In this research, to establish a kiln-drying schedule for poplar (Populus nigra) lumber with 75 mm thickness that cut down from North Khorasan province in Iran, with three schedules T5-D2 (Forest Product Laboratory), T5-D3 and T8-D5 were adapted for drying the lumbers down to the final moisture content of 8±2%. primary dry bulb temperature each three schedules was adjusted at 49,49 and 54°C and the final dry bulb temperatures was adjusted at 71,60 and 82°C respectively. Quantity of defects including warp and surface checks of the lumber were measured before and after the drying process in each stage. In order to analysis the lumber defects for estimating the best schedule, quality control graphs were used. Results of investigation indicated that drying of poplar lumber by using of the three schedules was desired. However the first schedule (T5-D2) had better drying characteristics than the other schedules.
M. Akhtari, M.Arefkhani