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The effect of water-repellent additives on the leaching of CCA from simulated southern Yellow pine decks
2000 - IRG/WP 00-50158
End-matched SYP boards were pressure-treated with CCA or CCA in combination with commercial water repellent additives. After fixation and drying, the boards were placed in plastic boxes and exposed outside in Harrisburg, NC. Plastic supports were used to keep the boards above the water collected. Over a period of five months, rain run-off water from 14 natural rainfalls were collected and analyzed by ICP. Metal leachate level was related to the type and level of water repellent additive present. Two commercial water repellents, which had much better water repellency than the third product, were found to be effective in reducing CCA leaching. Arsenic leaching can be reduced by over 35% in the presence of 1.2% of the two effective water repellents.
F Cui, P J Walcheski

Leaching of preservative components from pine decking treated with CCA and copper azole, and interactions of leachates with soils
2001 - IRG/WP 01-50171
Radiata pine decking was treated with CCA and copper azole preservatives to Australian H3 retention using conventional and modified Bethel schedules, and air-dried. Treated decking boards and durable hardwood controls were subjected to leaching in weather-exposed decks, and matching 19mm cubes were leached in extended AWPA E11-97 lab tests. Deck runoff and E11 leachate water was analysed after rain events and E11 change points. After 10 months, decks had lost up to 700mg Cu, 175mg Cr, 600mg As, 750mg B, 10 mg tebuconazole or 18000 mg tannin per square meter of deck, but flux rates had not yet reached zero for any component. Leaching from E11-97 blocks was much faster and greater than from the decks. Extending the leach period from 14 days to 50 days increased the amount of leaching by up to 40%. Even after 50 days, flux rates were measurable for most components. Deck leachates were applied to three soils using the draft OECD soil leaching column procedure. After elution, the soil was segmented and analysed. Although boron was more mobile than others, components tended to be retained in the topmost (first contacted) layer.
M J Kennedy, P A Collins

Effect of a water repellent additive on the performance of ACQ treated decks
2000 - IRG/WP 00-40168
The performance of a water repellent (WR) additive formulated for use with ACQ has been evaluated. The water repellency of wood treated with this formulation was studied in laboratory and field tests. The change in moisture content of ACQ/WR treated boards under field exposure conditions is compared with that of CCA/WR treated boards. Although the water repellency of the ACQ/WR system is lower than that of the CCA/WR system in laboratory tests, the field performance of both systems are equal after more than two years of natural weathering. The use of water repellent additives is clearly one of the options for optimizing the overall performance of copper based preservative systems.
F Cui, A R Zahora

Inorganic preservative levels in soil under treated wood decks after 8 years natural exposure in Borås, Sweden
2005 - IRG/WP 05-50233
Inorganic preservative components (Cu, Cr and As) were measured to a depth of 150 mm under deck structures made with Scots pine lumber treated with several different wood preservatives and installed in Borås Sweden 8 years ago. Higher contaminant levels were observed mainly under the drip lines and in the top 50 mm of soil. Under CCA treated decks, soil arsenic concentrations increased from background levels of about 3.5 mg/kg to 6-15 mg/kg in this zone. Copper and chromium levels were only slightly elevated above backgrounds of about 10 mg/kg and 3 mg/kg respectively. Copper levels were also only slightly elevated under decks treated with Tanalith E, Impralit KDS and Wolmanit CX-S. The Wolmanit CX-8 treated wood had concentrations averaging about 45 mg/kg in the top soil layer under the drip line while the Kemwood ACQ treated deck had concentrations above 100 mg/g in this zone.
P A Cooper, Y T Ung, M-L Edlund, J Jermer

Impact of leachates from CCA- and copper azole-treated pine decking on soil-dwelling invertebrates
2002 - IRG/WP 02-50183
This study assessed the short-term effects on non-target soil invertebrates of leachates from a naturally durable hardwood and timber treated with two copper-based wood preservatives. Natural rainwater leachates from kwila decking, and radiata pine-decking treated with CCA or copper-azole, were collected and applied on mown lawn soil in Brisbane, Queensland. The soil study consisted of 5 treatments: an independent control (replicates untreated), wet control (replicates treated with rainwater only), CCA, copper azole and kwila-extractive leachates. Two applications of each treatment were made. Soil samples were collected before application and then twice after the first application (3 and12 days) and 3 times after the second (3, 8 and 12 days). Soil arthropods were extracted from soil cores using Tullgren funnels. Frequency analysis and multivariate techniques were used to analyse the data for treatment effects. Soil invertebrates were dominated by mites (84%), which were identified to family level. We did not detect any difference in the density of mites except in the kwila-extractive leachate, where mite density increased significantly. However, there were detectable differences in mite community structure between all treatments, indicating differential effects of the treatments on the soil arthropod community.
N Crumière, A House, M J Kennedy

Recycling of CCA treated wood in the US
1998 - IRG/WP 98-50101-08
The production of CCA treated wood has increased dramatically in recent years. Previous estimates of the volume of treated wood to be removed were based on the assumed service life of the material, generally 20 to 25 years. This study based on a survey of contractors installing treated decks, determined that the actual service life of these decks is much shorter than their assumed functional service life. Home owners replace decks for various reasons beyond the soundness of the wood, including many reasons related to the look, appearance, and style of the deck. These new estimates of CCA treated wood likely to be removed in the near future greatly increases the volume destined for disposal primarily in landfills. This increases the pressure on these sites and may make competing disposal methods more attractive.
J McQueen, J Stevens, D P Kamdem

Relationship between coating properties and their performance on treated wooden decks
2008 - IRG/WP 08-30454
Preservative treated wood benefits from the application of a surface coating to protect it from weathering (UV and rain). Different preservative formulations may affect surface properties of treated wood differently; therefore compatibility of coatings with different preservative treated wood types should be considered. This paper examines coatings characteristics and their weathering performance when applied on different treated wood surfaces. The performance of a range of semi-transparent stains on chromated copper arsenate (CCA), alkaline copper quaternary (ACQ) and copper azole (CA) treated Southern pine wood was monitored over 18 months of natural weathering in Toronto, Canada. Additionally, the samples were tested under accelerated weathering conditions over a three month period. The ability of these coatings to reduce water uptake and leaching and general appearance of coated wood were measured, and the correlation with coatings properties such as: resin type, solvent base, surface tension, viscosity, density, solid content and pH was tested. The results showed that all coatings significantly reduced water absorption and preservative component leaching and higher viscosity stains had better performance in general. The coatings performed differently on different preservative treatments. Relative leaching performance was similar for accelerated and natural weathering exposure.
M Ahmadinejad, P A Cooper

Coconut lumber for wood decks (Cocos nucifera L.): decay resistance against Basidiomycetes fungi
2012 - IRG/WP 12-10784
Since a couple of years, manufactured products of coconut wood for outdoor uses like wood decks have been proposed on the European market. These are presented as an alternative for traditional tropical timbers. In the past, coconut wood was neglected and burned for sanitary reasons and lack of interest at industrial scale. Plantation coconut trees at end of production of copra constitute a renewable resource with high added value. In order to convince the markets, natural durability for outdoor use, without preservative treatment, against wood destroying fungi characteristic of northern temperate regions is a major property that has to be checked. Natural durability of coconut lumber was tested in the laboratory according to the European standard EN 15083-1 against brown (Coniophora puteana) and white (Coriolus versicolor) rot decay basidiomycetes fungi. Beech wood specimens were used as virulence controls. Mass losses were determined after 16 weeks exposure. The results showed that tested coconut wood is very resistant to the brown rot fungus Coniophora puteana and resistant to the white rot fungus Coriolus versicolor. Mass loss and density of tested samples with C. versicolor are inversely related. In addition, the density shows a large variability in the test sample, more than 500 kg / m³. These results confirm that after a selection on density criteria, the natural durability of Coconut lumber is sufficient for outdoor application in use class 3 (based on European standard EN 335 and in line with EN 460).
B Jourez, C Verheyen, J Van Acker

System treatments of Pinus sylvestris - influence on moisture, decay and discoloration
2013 - IRG/WP 13-30612
Biological activity can cause challenges for the use of wood in outdoor exposure. Decay and discolouring fungi influence the service life of wooden constructions, and the moisture content of the wood is often an important factor. The aim of this study was to evaluate the performance of different combinations of preservative/modified wood protection treatments and surface treatments for wooden decks in different exposure situations after ten years of field testing. Fourteen different wood protection treatments were tested, in addition to Scots pine sapwood, Scots pine heartwood and European larch heartwood. Furthermore two different surface treatments were included (alkyd oil with iron oxide pigments (AO) and alkyd emulsion without pigments (AE)) in addition to no surface treatment. The test setup used was the “Stapelbädds metoden”. The bottom layer is in soil contact and this stack method provides a moisture gradient within the five layers included. As expected a gradient of increasing wood moisture content and fungal decay rating was found from the top layer to the bottom layer of the stack. For samples with no surface treatment the treatments with lowest wood moisture content was Styren, Tanalith E7, Royal with pigment, European larch heartwood and thermal modification. In the stacks without surface treatment Royal with pigment and Gori SC 100 were the only treatments with decay rating ≤ 1 in all layers, while Scots pine sapwood, Scots pine heartwood and UltraWood all had decay ratings > 2 in all layers. AE surface treatment decreased fungal decay in all layers for furfurylation, Scots pine heartwood and Tanalith M. A similar trend including all layers was not found for AO. All treatments were totally covered by discolouring fungi with the exceptions of ACQ 1900 and Scanimp. Among the untreated samples European larch heartwood generally gave the best performance. The results show that moisture content and fungal decay rate can be reduced with the support of a surface treatment, but they also showed that the opposite can also be the case after ten years of field exposure.
A Schabacker, G Alfredsen, L Ross Gobakken, H Militz, P O Flæte

In-service performance of treated plywood bridge decks in Australia
2017 - IRG/WP 17-40794
Engineered wood products have a long history of use in bridge construction in Australia. The first bridges incorporating chemically protected engineered wood components were installed in the 1850’s and some survive to this day. Preservative treated plywood bridge deck panels have been employed since the 1980’s as a replacement for the more traditional hardwood plank decks. This paper reports on the condition of engineered wood bridge deck panels through an examination of core samples cut from preservative treated plywood decks after up to 20 years’ in-service. The panels had been manufactured using either; copper chrome arsenic (CCA) preservative in an envelope treatment process or an alkaline copper quaternary (ACQ) preservative in a veneer treatment process. The in-service performance of both types of panels is discussed in relation to results from preservative penetration and retention testing together with a consideration of the severity of the termite and decay hazards to which they were exposed. All but one deck panel were found to be sound, unaffected by decay, the exception was a panel that had been adequately treated but came from a location where it appeared that poor design or detailing had increased the decay hazard. This proven long term satisfactory performance of both envelope and veneer treated plywood panels in what is a particularly hazardous above-ground end-use suggests that current penetration requirements are appropriate for this product category.
M A Powell

Durability by design – a case study of the performance of wooden decks after 9.5 years of natural weathering
2019 - IRG/WP 19-20648
The service life expected for wood decking manufactured with poorly durable wood species, left untreated and exposed to severe environmental conditions such as high humidity and active biological agents, is usually assumed to be short (less than 10 years). The current classification of wood’s natural durability is based on EN standardised tests which do not fully reflect the real end-use conditions (such as outdoor decking or cladding), that might lead to underestimate the expected performance and service life of certain wooden commodities. In addition, design is known to play an important role in the performance of wooden elements over time, especially in the case of outdoor applications. With the aim of evaluating the positive impact of water-draining designs on wood’s service life, decks were manufactured using six wood species and up to six different designs, selected for their ability to generate or to avoid water traps through different design details. The decks were rated for fungal decay after 9.5 years of natural weathering in the city of Bordeaux, France. The results of the evaluation demonstrated that (1) significant difference in the ability of the decks to withstand decay over time exists depending on the design details used, the water-draining designs performing better than most of the water-trapping ones in the case of the non-durable spruce and poplar; (2) high variability in the resistance of the spruce and poplar deck boards against fungal decay was noticed for each tested design, but unexpectedly with a quite high percentage of boards of each type performing very well after such a long exposure to weathering; (3) the heartwood of larch, maritime pine and Douglas fir was found to perform very well after 9.5 years of weathering in decking application, with only slight differences observed between the selected designs, demonstrating that these species could be valued for decking applications despite their moderate natural durability.
M Kutnik, M Montibus

Performance of naturally durable decks after 15 years of field exposure
2020 - IRG/WP 20-10963
A decking test of Canadian species considered to be naturally durable was inspected after 15 years of exposure at test sites in Ontario and British Columbia. Based on the materials used in this experiment, Douglas-fir and yellow cypress had the greatest decay resistance, followed by eastern white cedar and western redcedar, and then by western larch and tamarack. All materials tested were more durable than the ponderosa pine sapwood control which had completed failed. Whether the wood came from old growth stands or second growth stands had little effect on decay resistance. Only old-growth Douglas-fir had significantly less decay than second-growth. The presence of sapwood reduced the decay resistance of yellow cypress, eastern white cedar and western redcedar, but did not impact the overall decay resistance of the less-durable western larch or tamarack. An initial coating of deck stain was associated with no change or slightly improved decay resistance.
R Stirling, D Wong