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Natural durability of European wood species for exterior use above ground
2003 - IRG/WP 03-10499
The main interest in using more timber for exterior constructions is to protect the environment, where wood is considered an environmentally friendly material. However, chemicals for wood protection are getting more and more restricted, consequently, the focus on the natural durability of wood is increased. Good, well-documented data on the durability of wood species in ground contact exist, which form the basis of the standard EN 350-2:1995. Yet, we have, however, no useful documentation for the natural durability of wood, when used outdoors above ground. The study is large-scale field trials, including more than 30 species, where the objective is to define and document the natural durability of European wood species when used outdoors above ground. The idea of the test set-up is to simulate different application situations of wood to recommend individual wood species for specific purposes – fit to purpose. Two basically different test set-ups are used: 1. Panels in close-to-practice applications: Horizontally oriented with and without covering. Vertically north turning and vertically south turning oriented with and without covering as well as 45 degrees south turning oriented without covering. 2. Lap-joints in standardised field exposures: The set-up is according to the CEN-standard ENV 12037: Wood Preservative – Field Test Method for determining the relative protective effectiveness of a wood preservative exposed out of ground contact – Horizontal lap-joint method. The paper presents the results of the appearance, the moisture fluctuation, mould growth and wood decay after 3 years field trial.
B Lindegaard, N Morsing

Durability of plywood made from soft- and hardwoods assessed according to ENV 12038 after artificial and natural ageing
2000 - IRG/WP 00-20191
Plywood was prepared from Norway Spruce and pure heartwood of Douglas Fir, Scots Pine, European Oak, False Acacia and Macoré using a phenol-formaldehyde glue. The panels of 38 mm in thickness were pre-conditioned according to the following procedures: a) 12 weeks storage at 20°C/65% rh, b) 2 weeks artificial weathering (with rain and UV-radiation at changing temperatures), and c) a natural weathering according to ENV 12037 for 3 month, 6 month and for 9 month whereby the ENV 12038 specimens were cut from the lap-joints. In general for softwood panels the decay was lowest after a 12 weeks` storage and the artificial weathering increased the decay rate more than the natural weathering applied. For False Acacia the durability was gained as predicted by EN 350-2 but not for the other species. Especially for European Oak and Macoré the durability was much lower than expected. Further, it has to be mentioned that the specimens usually showed a more intensive attack close to the nutrient media than at the top of the specimens. This indicates that the laboratory results might be influenced by the thickness of the panel tested because thinner material would be more equally degraded and thus would show a lower grade of durability.
H Leithoff, R-D Peek

Validity of above ground testing according to ENV 12037
2008 - IRG/WP 08-20379
The standard ENV 12037 for testing of treated and untreated wood (lap-joint) exposed above ground was issued in 1996 by The European Committee for Standardization. A draft for the development of the standard was presented by CEN-TC 38/WG 25/DOC N 076 in 2002. For a test to become valid the median rating of decay for untreated control replicates (Scots pine sapwood) must be equal or greater than 3.0. This paper presents results from a number of above ground tests in Uppsala, Sweden with untreated Scots pine sap- and heartwood, untreated European and Siberian larch heartwood as well as Scots pine sapwood treated with the reference preservatives TBTO and CCA. The untreated Scots pine sapwood demonstrated median decay rating of 3.0 after 6 to 7 years of exposure and an average service life in the range 6.5-8.5 years. Scots pine heartwood achieved median rating of decay 2.0 after 10 to 11 years and larch had median rating of decay 1.0 after 7 to 9 years of exposure. The median rating of decay for the reference preservatives TBTO and CCA was still 0 after 10 years of exposure.
Ö Bergman, U Råberg, N Terziev

Wood furfurylation process and properties of furfurylated wood
2004 - IRG/WP 04-40289
The first processes for “furfurylation” of wood (wood modification with furfuryl alcohol) were developed several decades ago. Furfuryl alcohol is a renewable chemical since it is derived from furfural, which is produced from hydrolysed biomass waste. Over the last decade modernised processes for furfurylation of wood have been developed. These new processes are based on new catalytic systems and process additives. Two main processes for production of furfurylated wood have been developed for WPT (Wood Polymer Technology ASA) by the authors – Kebony 100 for high modification levels of hardwoods and VisorWood for lower modification levels of pine. Commercial production according to the Kebony process has been running since August 2000, mainly for flooring. A small Kebony production plant is now in operation in Lithuania. A larger Kebony/VisorWood production plant started up in September 2003 in Porsgrunn, Norway. Several new plants operating according to the VisorWood process, each with an annual capacity of 10 000 m³ or more, are under construction. The properties of furfurylated wood depend on the retention of grafted/polymerised furfuryl alcohol (PFA) in the wood. At high modification levels (high retention of PFA) the enhancement of a wide variety of properties are achieved: an exceptional hardness increase, exceptional resistance to microbial decay and insect attack, high resistance to chemical degradation, increase in MOR & MOE, and high dimensional stability. At lower modification levels many property enhancements also occur, however to slightly lower extent. Notable are resistance to microbial decay and insect attack, increase in MOR & MOE, and relatively high dimensional stability.
M Westin, S Lande, M Schneider

The effect of storage or simulated internal use on the durability of wood based panels to decay fungi
1997 - IRG/WP 97-20106
Wood based panels such as particleboard and medium density fibreboard are experiencing a steady increase in use, in areas from structural to decorative applications. Understanding the "natural" durability of these panel products against basidiomycete fungal decay is therefore of great importance. Various methods have been proposed or are under development to test the durability/susceptibility of various panel products to decay. Our research has shown that if the fungal exposure methods detailed in the current European pre-standard (DD-ENV 12038:1996) are used to test boards fresh from manufacture, the susceptibility ratings observed are significantly lowered by the buildup of inhibitory substances in the test vessels. The effects of storing the boards before testing, in order to remove this effect have been studied with repeat biological tests carried out at intervals of 6 months. Our results show that even after 6 months storage the effect is reduced but not totally removed. The time after manufacture and the storage conditions are clearly significant variables affecting the "durability" of test specimens taken from the boards and therefore the incorporation of an appropriate preconditioning stage into the test is essential so that the effect is avoided.
S F Curling, R J Murphy, J K Carey

The resistance of wood coated with different solvent-borne paints against colonisation by decay fungi
2009 - IRG/WP 09-40468
This paper examines different solvent-borne paints characteristics and their decay resistance when applied on pine wood surface. It was determined by the standard ENV 839 procedure. The part of samples were subjected to accelerated ageing according to the EN 84 standard. The discussed commercial paint systems were typical stains or penetrating oil-based products, with or without biocides.
B Mazela, P Hochmańska

Evaluation of the european standard ENV 12038 for durability testing of plywood
2001 - IRG/WP 01-20237
The latest improved version of the standard ENV 12038 drafted as document N44 by CEN Technical Committee 38 (WG 7 - WG 23) is used to evaluate the effect of wood composition and structure on plywood durability. The method described is based on the agar-block test of the EN 113 standard used for the determination of the efficacy of wood preservatives and the assessment of the natural durability of timber. This test method differs from the soil-block test commonly used in North America and vermiculite test procedures used earlier for plywood testing. The ENV 12038 method is essentially developed to deviate minimal from the European basidiomycete tests currently established. Therefor it was important to evaluate whether or not vermiculite or soil as a test medium could be replaced by a malt- agar medium using an adequate preconditioning of panel specimens prior to fungal testing. Based on two consecutive experiments both test methodology and the assessment of plywood durability are investigated. Plywood is a material that allows a direct evaluation of test methods for assessing the durability of board materials in comparison with test methods used for solid wood. The presence of glue-lines and the layered structure based on solid wood veneers enables to investigate in detail the impact of wood composition as well as the type and amount of glue. Preconditioning plywood prior to testing according to ENV 12038 proved to be essential. However the impact of the glue is not entirely eliminated that way.
J Van Acker, M Stevens, E De Clercq

The effect of alternative pre-conditioning procedures on the durability of wood based board materials to decay fungi
1997 - IRG/WP 97-20105
In the biological testing of wood based board materials it has been shown that exposure of boards in a closed vessel system may lead to inaccurate results due to the build up of volatile substances that inhibit the test fungi. It is thought that this is a transitory effect of freshly manufactured boards. In the European standard for testing fungal durability of board materials which is currently under development (DD-ENV 12038:1996), a leaching pre-conditioning method is used to remove this effect. A variety of alternative ageing procedures have been studied, including natural weathering, leaching and evaporative procedures, to determine the most appropriate pre-conditioning protocol for the decay test. Our results show that there are procedures which are more efficient, and possibly more meaningful in terms of effectiveness or appropriateness of regime for use on board specimens.
S F Curling, R J Murphy, J K Carey

Suitability of cotton strip testing as a screening method for the development of wood preservative formulations
2003 - IRG/WP 03-20270
This paper outlines a simple and rapid test method for screening the efficacy of wood preservative formulations against microbiological attack using cotton strips. The method was evaluated against soft rot and was found to provide reliable information on the protection of lignocellulosic material against microbiological attack. The assessment is based on visual interpretation of decay and on a simple strength test of the cotton strip. The experience obtained with this method at BFH and BAM by testing in parallel a well investigated copper containing preservative revealed a good prediction of the effective concentration on wood. The results of the cotton strip screening test were compared with ENV 807 test results as well as with data from fungus cellar testing (5 year results) and a field trial (EN 252, 5 years).
H Leithoff, I Stephan, H Härtner

Modelling of copper emission fron treated wood leached according to NEN 7345 and ENV 1250.2
1996 - IRG/WP 96-20097
A series of water leaching experiments is carried out investigating pine and spruce treated and fixed using different copper-containing preservative solutions and process technologies. Water changes took place as prescribed in the Dutch standard NEN 7345 and the European test method ENV 1250.2, each of the leachates being chemically analysed for their copper content. Irrespective of the preservative treatment, though related to the method of testing, all leaching data are modelled using two existing time dependent emission formulas. Long term predictable environmental copper concentrations are calculated and discussed with respect to the leaching method used and the acceptability of the Cu emission level gained.
G M F Van Eetvelde, S G L Michon, M Stevens

Service life prediction of plywood
2007 - IRG/WP 07-20367
Plywood is the wood based panel showing the best physical and mechanical properties for application under moist construction conditions. Appropriate physico-mechanical durability for exterior applications in transportation or construction systems can be guaranteed by assessment of the glue bond quality and mechanical characteristics. However, due to the fact that mainly non-durable wood species are used for plywood production, there is a need to specify the biological durability of plywood in relation to service life. With the European standard ENV 12038 a tool is available to evaluate the intrinsic biological durability of plywood material. According this standard plywood has to be tested against wood rotting basidiomycetes using a test procedure equivalent to the EN 113 procedure for the assessment of wood preservatives when testing of solid wood. Testing a large amount of different commercial plywood products according to this standard showed that the test procedure is too severe, offering no possibility to differentiate between panel types (e.g. the influence of a coating could not be distinguished). To be able to use the ENV 12038 as an aid for service life prediction the test procedure needs to be adapted and the results need to be linked to data collected during outdoor field testing. Service life prediction of plywood requires a combination of durability testing and evaluation of moisture related properties, and relates this to data collected during outdoor field testing and in service data (derived from e.g. surveys). Furthermore there is a need to identify a simple methodology to interrelate product properties and intended service life for different use class conditions. This paper suggests an approach to enable implementation in practice for plywood.
J Van Acker, J De Smet

A Comparison of the Performance of Related Copper Based Preservatives against Soft Rot
2010 - IRG/WP 10-30540
The performance of pine and beech wood treated with either a soluble copper + quat (ACQ type D) preservative system or a particulate copper + quat system was evaluated in unsterile soil using the European standard ENV 807 soft rot decay test procedure. In addition, to compare soft rot performance of soluble and particulate copper directly without the influence of co-biocides, beech and pine test blocks were treated with either a soluble copper formulation or particulate copper system to equivalent copper retentions and then exposed to mixed cultures of soft rot fungi in a vermiculite medium according to ENV 807 Annex A. Relative performance of the different formulations was determined using weight loss data.
M Ray, D Dickinson, K Archer

Durability testing of coconut shell according to ENV 807
2011 - IRG/WP 11-10761
Coconut shell was tested in the laboratory according to the European standard ENV 807 with three different soil types: compost soil, brown rot/soft rot rich soil and white rot/soft rot rich soil. Mass losses between 14 and 16 % were achieved with all three soils, indicating that the decay type is of little importance in the degradation process. Somewhat higher mass losses, 19-22 % were obtained for the durable/moderately durable, according to EN 350-2, wood species Sipo (Entandrophragma utile), whereas preservative-treated references had significantly lower mass losses, 0.5-7 %. The results of the test were promising but further experiments and testing will be necessary to explore the full potential for coconut shell to be used e.g. for composite materials with enhanced durability against decay fungi.
J Jermer, A H H Wong, K Segerholm, T Nilsson

Visual Inspection – How Important is the Influence of the Evaluator?
2013 - IRG/WP 13-20521
Visual inspection is often a crucial means of judging the efficacy and performance of a preservative. It is used in non-destructive testing in long term exposure trials or simply, when the practical use and precision of the human eye is a good means of measure. As for the procedure described in EN 252, the impression of softness due to decay of the wood has also to be considered. Although, a thumb and an eye are unequivocally refined sensors, there is no method published for their calibration according to the method they are used in. So, quality assurance of visual inspection is often neglected. This paper proposes a procedure that may lead to constructive discussion and harmonisation of the interpretation of rating scales among evaluators. It is based on the experience of European countries within the Nordic Wood Preservation Council (NWPC) and CEN/TC38 WG 25 working on the clarification and correct interpretation of rating scales as in EN 252. During three workshops, practical work was performed on wood stakes from the field showing different levels of attack by fungi. In average all evaluators agreed on the evaluation in 21% of the cases, while at least one evaluator disagreed in 67%. In 12% of the cases the stake was given three different ratings. A following discussion led, in almost every case, to agreement on a rating class according to EN 252. We suggest that especially accredited laboratories that perform this type of testing regularly participate in such workshops to "calibrate" themselves with their colleagues and the intention of the standards. A procedure, as described in this paper, for performing quality improvement of the evaluation according to the rating scale could be useful as an informative annex in all standards where visual inspection is used, e.g. EN 252, EN 330 and CEN/TC 12037.
M Klamer, P Larsson Brelid, I Stephan

Copper leaching from copper-ethanolamine treated wood during exposure to terrestrial microorganisms
2013 - IRG/WP 13-30621
Copper-ethanolamine based wood preservatives are still the most important solutions for protection of wood in ground applications in Europe. Wood in ground is exposed to variety of organisms, which can act synergistically. In order to simulate these conditions in laboratory, Scots pine (Pinus sylvestris) specimens impregnated with copper-ethanolamine preservative of three different concentrations (cCu = 0.125%; 0.25% and 0.5%) were exposed to three different soils according to the ENV 807 procedure for periods between 12 weeks and 32 weeks. After respective periods of exposure, samples were isolated and their mass loss, bending strength and modulus of elasticity were determined. In the final step remaining copper in the samples was determined. The results showed that in spite of the prominent copper leaching, tested copper-ethanolamine treated wood exhibited good performance in ground applications. Furthermore, it is evident, that there is a good correlation between mechanical properties and mass loss determined, regardless of the chemical treatment applied.
M Humar, N Thaler, B Lesar

Impact of water holding capacity and moisture content of soil substrates on the moisture content of wood in terrestrial microcosms
2019 - IRG/WP 19-20662
Terrestrial microcosms (TMC) are frequently used for testing the durability of wood and wood-based materials as well as the protective effectiveness of wood preservatives. In contrary to experiments in soil ecology sciences, the experimental set-up is usually rather simple. However, for service life prediction of wood exposed in ground, it is of immanent interest to better understand the different parameters defining the boundary conditions in TMC. This study focussed therefore on the soil-wood-moisture interactions and their potential effect on durability testing in TMC. TMC were prepared from the same compost substrate with varying water holding capacity (WHC) and soil moisture content (MCsoil). Wood specimens were made from English oak, Beech, Douglas fir, and Scots pine sapwood and exposed to in total 48 different TMC and wood moisture content (MCwood) was studied as well as its distribution within the specimens. For this purpose the compost substrate was mixed with sand and turf and its WHC was determined using two methods in comparison, i.e. the ‘Droplet counting method’ and the ‘Cylinder sand bath method’ in which the latter turned out advantageous over the other. MCwood increased generally with rising MCsoil, but WHC was often negatively correlated with MCwood. Instead, the degree of water saturation Ssoil could serve as a more predictive measure for MCwood in soil exposure scenarios. With increasing Ssoil the MCwood increased, but followed wood species-specific curves with differently steep increase and a plateau at Ssoil = 0 %. In addition, Ssoil from which MCwood increased most intensively was found to be wood-species specific and might therefore require further consideration in soil-bed durability testing and service life modelling of wooden components in soil contact.
C Brischke, F L Wegener

Copper-octanoate - a potential reference preservative replacement for CCA in field test standards?
2022 - IRG/WP 22-20688
Finding a CCA reference replacement for use in standardised test methods is of high priority since this chemical is being phased out and may in the near future be banned also for experimental and approval purposes. In this paper we assess the possibility to replace CCA reference preservative with an historical copper octanoate product. There is a huge amount of lab and field test data available for a copper octanoate preservative, “Cuprinol Tryck”, which was in use in the Nordic countries during the 70s and 80s showing that it might work as a substitute for CCA in test standards. We managed to reproduce the production process for this preservative in laboratory scale. In this study, we have examined the copper octanoate product from an impregnation point of view as well as from a wood protection point of view. Impregnation related results show that copper octanoate has a liquid uptake in wood that is significantly better than water (as measured with Wilhelmy plate), that the impregnation liquid readily penetrates the sapwood in samples mimicking poles of 15 x 15 cm cross-section. ENV 807 tests showed that a retention of 1,9 kg Cu/m³ (21 kg product/m³) fully protected the wood against biological attack in both soft-rot dominated garden compost soil and brown rot dominated sandy soil, to a level equal to CCA 9 kg/m³ and CC 10 kg/m³, while a retention of 0,6 kg Cu/m³ reduced mass loss to approximately the same extent as CCA at low retention level (2 kg/m³). These results are in accordance with old results from field test with Cuprinol Tryck in several Nordic test fields. In order to evaluate the correlation in degradation between CCA and Cuprinol Tryck in field testing according to EN 252, series of retentions reflecting the sample copper levels have been prepared for a Round Robin test. These will be installed in a number of test sites during spring 2022. Results from these experiments will be reported in future papers. Based on our current results, we conclude that the copper-octanoate preservative product would be a potential substitute for CCA in standardized durability testing.
R Ringman, M Westin, M Klamer, A Christof, F Friese