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Adhesion durability of the thinnest CLT in Japan treated by solvent recovery system
2019 - IRG/WP 19-40882
The purpose of this study is to clarify the adhesion durability of the thinnest CLT (36 mm thickness) in Japan impregnated with preservatives (azole neonicotinoid compounds (AZN)) under solvent recovery system so called “dry pressure process” for long-term durability. The adhesion durability tests were conducted in accordance with the Japanese Agricultural Standard (JAS) of Cross-Laminated-Timber (2013), and the peeling tests and the block shear tests were performed. As a result, the AZN treated CLT retained sufficient adhesion durability.
K Kawakami, W Ohmura

Effects of acetylation on the dimensional stability and decay resistance of kenaf (Hibiscus cannabinus L.) fiberboard
1996 - IRG/WP 96-40059
The objective of this study was to investigate the influence of the acetylation treated kenaf fiber, Phenol formaldehyde resin content level, and three fungi species on the dimensional stability and decay resistance of high density non wood composition boards. A standard ASTM method was used to evaluate weight loss and thickness change. The linear shrinkage and expansion of each species were also determined. All specimens were exposed to decay chambers for 16 weeks. Test results indicated that most of the main factors significantly influence the thickness, length changes, and decay resistance of the high density kenaf fiberboards.
P Chow, T Harp, R Meimban, J A Youngquist, R M Rowell

Analysing the characteristic role of moisture content for drying and fluid flow in Sitka spruce. - Part 1: The drying process of sapwood and heartwood of two different thickness of Sitka spruce using a kiln. - Part 2: Effects of moisture content on longitudinal permeability of Sitka spruce in vertical variation of the tree
2000 - IRG/WP 00-40173
The characteristic role of the moisture content in Sitka spruce (Picea sitchensis (Bong.) Carr.) that grown in the United Kingdom was examined by this study on the basis of (1) the reduction of moisture content in two different thickness of sapwood and heartwood by kiln drying process, and (2) the effects of moisture content to the longitudinal void volume filled of tanalith-C by the full-cell process from base (1 m) to apex (3 m) of the tree in sapwood zone. Accordingly, conclusions on indication of the drying process of sapwood and heartwood, and vertical variation of longitudinal flow with effects of moisture were listed separately: (1) Comparison of Drying Characteristic of Sapwood and Heartwood: The two different thickness (300x30x30 mm3 and 300x20x20 mm3) of sapwood and heartwood of Sitka spruce was dried using the suggested drying schedule in kiln. The reduction of moisture was schematically diagrammed according to sapwood and heartwood stakes. The reduction of moisture followed the same downward trend that sapwood (S) loses more moisture than heartwood (H) although the small stakes of S and H lost moisture rapidly compared with the large ones. (2) Vertical Variation of Moisture Content and Longitudinal Permeability: The 90 kiln dried defect free sapwood stakes (150x25x25 mm3) of Sitka spruce was taken from base to apex of the trees at 1, 2 and 3 m above ground level. After having the determination of moisture content in each experimental stake, the treatment was carried out by the full-cell process with CCA preservative (Tanalith-C) using a model pressure treatment plant. Significant differences observed among the tree heights from 1 to 3 m showing that slightly increases of moisture content from base to apex and conversely decreases of longitudinal void volume filled by preservative fluid.
I Usta

Treatment of particleboard with isocyanate resin to impart improved dimensional stability and water repellency
2000 - IRG/WP 00-40178
Standard particleboard panels (for interior use) of 16 mm nominal thickness were cut into samples measuring 6.4 mm x 78 mm2. The samples were divided into 4 end matched batches. Two batches were treated with isocyanate resin and cured. The other 2 batches were left untreated. One of the treated batched and 1 of the untreated batches were edge sealed with epoxy resin prior to isocyanate resin application. The weight and thickness of each samples was measured prior to placing the sample in a beaker of distilled water. The weight and thickness were measured periodically for 1 week. Treatment with isocyanate resin reduced the average weight gain of sealed samples compared to the controls after 1 week. The average weight gain after 144 hours was 37% and 63% respectively while unsealed samples achieved a weight gain of 37% and 100% respectively. The thickness swelling was also reduced in the sealed samples compared to the controls (10% and 17% respectively) and the unsealed samples had a thickness swelling of 9% and 21% respectively. The results show a reduction in the rate of moisture uptake (water repellency) and amount (dimensional stability). Further experiments are described comparing particleboard with solid wood, with and without isocyanate resin application.
K M Filcock, P Vinden

Information from COIPM Wood Group
1985 - IRG/WP 4120
During the last COIPM Meeting (which took place in Athens, Greece in September 1984) the Wood Group met and discussed the co-operative work 'Durability in sea-water of wood with plastic wraps and wood treated with polymere'.
A Gambetta

An Open Letter to Proponents of CLT/Massive Timber
2016 - IRG/WP 16-40755
We present an Open Letter that discusses the need to address the potential for biodeterioration in CLT/Massive timber structure. We invite members to review and sign the document. We also welcome suggestions for potential recipients.
A Taylor, J Lloyd, T Shelton

Ancillary properties of vapor boron-treated composites
2001 - IRG/WP 01-40210
This paper discusses the water absorption, thickness swelling, and internal bond strength of North American composites treated using a vapor boron treatment process. For oriented strandboard, high boron loadings led to lower internal bond strength and lower thickness swelling. Water absorption results were variable but no deleterious effect of treatment was noted. For medium density fiberboard, the highest loadings led to reduced internal bond strength. Thickness swelling decreased with increasing boron level, but not significantly. As with OSB, water absorption results varied.
W A Jones, H M Barnes, R J Murphy

Biodegradation of acetylated southern pine and aspen composition boards
1994 - IRG/WP 94-40020
This objective of this study was to investigate the influence of the acetylation treated wood fiber, Phenol-formaldehyde resin content level, two wood fiber species, three fungi species on the dimensional stability and decay resistence of high density composition boards. A standard ASTM method was used to evaluate weight loss and thickness change. The linear shrinkage and expansion of each species were also determined. All specimens were exposed to decay chambers for 16 weeks. Test results indicated that most of the main factors significantly influence the thickness and length changes and the decay resistance of the high density composition boards.
P Chow, T Harp, R Meimban, J A Youngquist, R M Powell

A Preliminary Report on the Properties of Engineered Wood Composite Panels Treated with Copper Naphthenate
2005 - IRG/WP 05-40294
This paper reports on our preliminary investigation of the properties of randomly oriented strandboard which had waterborne or powdered copper naphthenate (CuN) incorporated into the board during manufacture. When compared to zinc borate-treated controls (ZnB), the mechanical properties of strandboard (MOR, MOE, work-to-maximum load, internal bond strength) were not adversely affected by treatment with either form of copper naphthenate. In general, values for mechanical properties followed the trend untreated controls > waterborne CuN = powdered CuN > ZnB. Water absorption and dimensional properties followed a similar trend. This preliminary study suggests that CuN is a viable alternative treatment for engineered wood composites.
J W Kirkpatrick, H M Barnes

Decay Resistance and Bonding Properties of Structural Flakeboard
2002 - IRG/WP 02-40233
Experimental structural flakeboard panels consisting of differing furnishes and resins were produced and tested for internal bond, linear expansion, thickness swell, and decay resistance. One group of panels was produced with recycled CCA-treated wood as the furnish and commercial phenol formaldehyde (PF) resin as the binder. Other groups of panels were produced with either mixed hardwoods or southern pine as the furnish and then sprayed with a co-reacted soy-flour PF resin or a commercial face or core resin. The recycled CCA-treated panels contained 5 different furnish ratios (0:100, 25:75, 50:50, 75:25, and 100:0) of recycled CCA-treated southern pine and virgin, untreated southern pine. Tests on the panels bonded with co-reacted soy flour PF indicated that 30% substitution of phenol with soy flour in the resin system did not appreciably promote decay or reduce IB strength. As expected, panels produced with a higher ratio of recycled CCA-treated wood furnish, were generally subject to less weight loss during decay tests for brown rot (Gloeophyllum trabeum, ATCC 11539) and white rot (Trametes versicolor, ATCC 42462) but yielded lower IB values. Research in currently in progress to assess the resistance of all the aforementioned panel types to the Formosan subterranean termite (Coptotermes formosanus Shiraki).
T F Shupe, Chung-Yun Hse

Study of modulus of rupture, circumference taper, sapwood thickness and CCA treatment of Norwegian origin Pinus sylvestris poles
1994 - IRG/WP 94-20054
Nondestructive strength testing with Pilodyn (6J) of Norwegian Pinus sylvestris poles revealed effective modulus of rupture (MOR) of 54.39 N/mm² at wet conditions after CCA-C treatment and circumference measurement revealed circumference taper of 0.021 m/n. Sapwood thickness or penetration of CCA-C study revealed that 77% poles were with sapwood thickness equivalent to 39.6% of radius of poles and above, 72% poles were with sapwood thickness equivalent to 40% of radius of poles and above and 59% poles were with sapwood thickness equivalent to 44% of radius of poles and above. Noted that 19% poles were within the sapwood thickness range of 39.6 to 40% of radius of poles and 14% poles within the sapwood thickness range of 40 to 44% of radius of poles. Proper selection of poles before and after preservative treatment regarding desired sapwood thickness would eliminate undesirable poles for REB. X-ray spectroscopic analysis revealed mean retention of dry oxides of CCA-C of w/v 20.58 kg/m³ sd 2.53 (w/w 4.28% sd 0.52) in an assay zone of 2.5 to 45 mm. Regular maintenance of chemical balance of individual component of CCA-C before preservative treatment would be more suitable to have balanced retention of individual component of CCA-C.
A K Lahiry, S Begum, G N M Ilias, M A B Fakir, R U Hafiz

Durability of Wood/Plastic Composites Made From Parthenium species
2002 - IRG/WP 02-40225
Previous study indicated that the natural chemical constituents of the guayule plant (Parthenium argentatum) improved some durability properties of wood when it was treated with resin extracted from guayule. At present, there are about a dozen species of Parthenium growing in the North American continent. P. argentatum is the only species with harvestable amounts of the rubber latex. Other species such as P. incanum and P. tomentosum produce primarily resinous materials, but which could be as useful as the P. argentatum species for making composites. The predicted commercialization of guayule for its hypoallergenic latex will result in a significant amount of waste plant material or bagasse that can be put to use in making wood products and would otherwise be a disposal problem. Thus, the guayule fiber residues can be a source of natural wood preservative to improve the durability of wood/plastic composites. Preliminary laboratory tests were conducted to determine the resistance of wood/plastic composites made from three Parthenium species against Eastern subterranean termite. The physical properties of these three types of composites were also measured, namely dimensional stability (water absorption, thickness swelling, two-hour boil, and linear expansion), and the strength properties such as bending and internal-bond (IB) or tensile stress perpendicular to face. The results were compared with a wood/plastic composite made from the commercial pine wood flour or fibers.
P Chow, F S Nakayama , J A Youngquist, J H Muehl, A M Krzysik

Preliminary investigation on the natural durability of Guayule (Parthenium argentatum)-based wood products
2000 - IRG/WP 00-40154
Conventional preservatives used to protect wood from insect and microbial damages are presently of major concern to human health and the environment. Finding alternative and economical preservatives has not been successful. Previous studies have shown that the resinous material extracted from the guayule plant (Parthenium argentatum, Gray) has both insect- and microbial-resistant properties. Unfortunately, it has not been accepted commercially because of the lack of an adequate supply of the raw material. However, the potential domestication of the guayule plant to produce hypoallergenic rubber latex will result in the production of large amounts of waste wood material. This should provide opportunity to use this natural source of the biologically resistant resinous chemicals. The objective of this preliminary study was to determine the effects of the rubber latex-removed wood residues or bagasse and the resinous extracts on termite- and decay-resistant properties. Two types of test materials were used in the study. One was wood impregnated with organic-solvent extracted resinous material from the plant. The other was composite wood fabricated using the residue or whole plant and plastic binder, which was used to improve the physical properties of the composite. Accelerated laboratory tests were conducted to determine the resistance of the wood products against the Eastern subterranean termite and wood fungi (brown-rot). The wood and stem of the guayule plant, wood treated with the resinous extract, and particle and composite wood made from ground guayule exhibited termite and wood fungal resistance.
F S Nakayama, P Chow, D S Bajwa, J A Youngquist, J H Muehl, A M Krzysik

Wood cement composites using spent CCA treated wood
1999 - IRG/WP 99-50126
The feasibility of using spent or out-of-service CCA treated wood as a component of wood/cement composites was evaluated. Cold pressed wood particle cement boards were made using CCA treated particles from a red pine (Pinus resinosa Ait.) pole removed from service and from untreated red pine wood from a new pole. Boards were manufactured using a range of wood to cement ratios and water to cement ratios. After curing the boards were evaluated for bending strength and stiffness, internal bond strength, water absorption, thickness swell, decay resistance and CCA leaching properties. The inclusion of CCA treated wood in the composite resulted in improved physical and mechanical properties compared to board made with untreated wood. There was also evidence of improved decay resistance in boards with spent CCA treated wood. Arsenic and copper leaching losses were very low from the wood cement composite compared to leaching from equivalent amounts of CCA treated wood. However, chromium leaching rates were not reduced.
Chen Huang, P A Cooper

Preservative treatment of round bamboos by a new technique - Some further studies. Part 1
1990 - IRG/WP 3607
In general, the easy susceptibility of bamboos to wood destroying agencies is a major constraint in its rational utilisation. This is more so in tropical countries like India where wood destroying agencies are quite active. In an earlier publication, it was reported that round bamboo specimens of Bambusa balcooa, having three nodes, could be satisfactorily treated by CCA by a new technique developed at the R & D laboratories of Ascu India. It was also stated that further experimental work was in progress with longer specimens. Details of the results obtained so far are reported in this paper.
V R Sonti, B Chatterjee

Study on the thickness swelling of mould-resistant chemical treated bamboo strand woven outdoor flooring
2010 - IRG/WP 10-40489
To prevent bamboo strand woven flooring from mould, several preservatives were chosen to treat bamboo strand before dipping into adhesives and pressing. The thickness swelling and mould resistant effect of the finished board were studied. Results showed that different preservatives had different influences on the thickness swelling of BSWF, and in order to reduce the thickness swelling of the finished board, bamboo strands should be dried to certain moisture content after treated with preservatives. Water-based organic fungicide preservative (ZJFC-Ⅰ) and the compounds of CCC and Propiconazole (PPA) (ZJFC-Ⅱ) when dried to certain moisture content, had no or little influences on the thickness swelling of BSWF, which were 14.5% and 14.7%, respectively, a little higher than water treated controls (13.3%), and much lower than ACQ treated ones (20.7%). But if the treated strands were simply air-dried, the thickness swelling of manufactured board were very high. Laboratory mould resistant test showed that ZJFC-Ⅰ and ZJFC-Ⅱ were the most prospect preservatives for BSWF. But a lot of test should be carried out in the field for outdoor application.
Fangli Sun, Binfu Bao, Shenyuan Fu, Anliang Chen

Chapter 11 - Preservation of talla bamboo
2007 - IRG/WP 07-10635-11
Researches revealed that the talla bamboo (Bambusa tulda Roxb.)) in Bangladesh could be full-cell pressure treated with CCA in green and dry conditions. The dry bamboo gives higher loading absorptions than green one when impregnated at same treating conditions. Also higher absorptions are obtained at nodes rather than internodes. Adequate penetration and retention results for ground and water contact uses are only possible by treating bamboos pre-dried to 10-15% MC. The green bamboo is easily treatable for indoor and overhead outdoor uses. The service life of this socio-economically important bamboo can easily be increased at least two times than nominal by CCA treating either green or dry bamboo. Two small holes made before pressure treatment in each internode will give split-free bamboo.
A K Lahiry

Chapter 12 - Treatment Groups of Bamboo
2007 - IRG/WP 07-10635-12
Study on distribution of CCA in three major bamboo species in Bangladesh, full-cell pressure treated at green and dry conditions revealed two treatment groups and some treating principles. Higher adequate treatment for ground and water contact use is only possible by treating problematic bamboo species pre-kiln dried up to half of its FSP and non-problematic species pre-dried up to FSP (20% MC). The non-problematic species can be treated in green conditions for indoor and overhead outdoor uses. Two smallest holes made before treatment in each internode will give split-free bamboo.
A K Lahiry

Effect of preservative treatment on dimensional stability of plywood made of treated simul (Bombax ceiba) veneer
2012 - IRG/WP 12-40575
The dimensional stability such as thickness swelling and water absorption of plywood made of treated simul (Bombax ceiba) veneers were investigated after 2 hours and 24 hours soaking under water. The veneers were treated with hot water and cold water solution of borax-boric acid (1:1), neem leaves and mahogany seeds of different concentration (1:10, 1:20, and 1:40) at different treatment duration. It was observed that the values of swelling were increased with the increase of soaking time from 2 hours to 24 hours. In the case of plywood made of borax-boric acid treated veneers, the percentage of swelling were increased with the increase of borax-boric acid concentration. The values of thickness swelling were also increased with the increase of treatment duration from 20 minutes to 60 minutes and 1 to 3 days. The values of swelling obtained in plywood made of neem leaves and mahogany seeds treated veneers were higher than that of borax-boric acid treated veneers and near to the untreated samples. The mean values of percentage of water absorption in plywood after 2hrs and 24 hours water soaking were determined. It was found that after 24 hours soaking, plywood made of mahogany seeds treated veneers absorbed more water than that of neem leaves treated veneers. All the values obtained from treated samples after 2 hours and 24 hours soaking were lower than the control samples. But it was observed that higher amount of water was absorbed in neem leaves and mahogany seeds treated board in comparison with borax-boric acid treated board. It was also noted that the values of water absorption in leaves and seeds treated board were near the values of untreated samples.
K Akhter, M Mahabubur Rahaman, A Ara

The durability of manufactured structural building materials
2016 - IRG/WP 16-40718
The projected market potential for Engineered Wood Products such as CLT (cross laminated timber) is very positive however, potential prolonged rain leakage or moisture exposure during construction and in-service could pose considerable concern for its durability and reputation. This research was conducted to assess the decay resistance of CLT and OSB (oriented strand board) in an accelerated trial. This testing method is used in establishing the effectiveness of wood products in framing subject to intermittent wetting. The results showed untreated OSB and CLT were very susceptible to decay. However, in the case of CLT, decay can be prevented by surface application of boron preservative. There is a need to harmonise Standards for CLT and OSB timber used in building.
T Singh, D Page

Corrosion verification experiment of the screw driven into CLT
2017 - IRG/WP 17-40816
Japan has abundant forest resources, but we depend on import for 70 percent of the consumed timber. Japan has the vision which promotes the timber self-sufficiency rate 30% to 50% by 2020. Therefore CLT attracts attention as a new timber material. Japan has a climate with high temperature and humidity, and wooden buildings are often treated with chemicals as a measure against biological deterioration of timber. It is the same for the case of CLT. However, chemical treatment for all layers of CLT requires a huge cost. Therefore chemical treatment every each layer is considered. When chemical treatment is carried out for each layer, macrocell corrosion may occur on penetrating screws, due to an electric potential difference generated between the layer chemical treated and the layer not treated. This study aims to expand the limits of wooden buildings, and aims to expand the demand on timber for new applications such as large facilities and middle-high-rise buildings. In this study, we experimentally evaluated the corrosion of screws in CLT which full-layer chemical treatment, each layer chemical treatment (3 layer and 2layer), and without chemical treatment, for verifying the effect of chemical treatment on metal joints. As a result, the following was clarified. 1. It seems that the amount of chemical has more influence on rust of screws. Because screws in CLT with full-layer treatment are most rusted. 2. The macrocell corrosion wasn't observed in this study. However, it seems necessary to do more inspection because the weight remain ratio can't be confirmed only more than about 97 %.
N Wada, H Ishiyama, S Yamamoto

Water absorption characteristics of CLT
2017 - IRG/WP 17-40817
CLT is initialism of Cross Laminated Timber. CLT is generally large-sized panel which can use many woods efficiently, so it is attracted attention recently in Japan. Therefore, many studies about CLT are carried out. However, there are few studies about durability of CLT. Avoiding water infiltration is important for durability of wooden building. CLT has many edge-glued points which has risk of water intrusion due to capillary phenomenon. So we focused on water absorption from the bottom end of the wall by accidental water infiltration. In this study, water absorption from the edge-glued point of CLT was experimentally verified. As a result, the following was clarified. 1. A water stay at the bottom part in case the fiber is in the transverse direction. 2. Water reaches the upper part in case the fiber is in the longitudinal direction because of probably capillary phenomenon.
D Yokoi, H Ishiyama, Y Hirano

In-line quality control of the film thickness in industrial coating processes for exterior cladding
2018 - IRG/WP 18-40835
The production of industrially coated wood cladding has been strongly increasing in Scandinavia during the last years. In the beginning of this development, industrial coating processes included solely the application of pigmented primers; these however provide only a short protection of the wood surface and the application of a top coat is required during the first 6 to 12 months after mounting the cladding boards. In recent years, the trend has been going to an industrial application of several coats to extend the maintenance interval for repainting. The Norwegian company Gausdal Bruvoll SA is currently starting up Scandinavia’s largest and most modern plant for industrially coated cladding, and aims to implement an advanced process control system that 1) enables automated monitoring and documentation of process and product properties, and 2) provide input data for multivariate analysis and prediction models that will contribute to process and product optimization. The development of this inline quality control system is subject to the ongoing research project KonTre (2017-2019). During the first project year, KonTre’s consortium has mainly worked in laboratory scale to develop, adapt and test appropriate measurement systems for in-line control in Gausdal Bruvoll’s new coating line. The work dealt with non-destructive methods to determine spraying and color failures, coating film thickness, microfoam, wood moisture content, and sub-surface temperature in cladding. The present paper describes the development towards industrial coating application on exterior wood cladding in Scandinavia during the last years and discusses the feasibility of using thermal optics for in-line film thickness measurements.
U Hundhausen, M Slabohm

Development of accelerated decay test for CLT using a fungus grown on agar medium
2019 - IRG/WP 19-20664
CLT is a large-scale wooden board which consists of several layers of sawn lumber stacked in altering directions. Therefore, a lot of large cross sections appear on all narrow faces of CLT. As water penetrates easily into timber from cross section, wooden material whose cross section is exposed to water in in a usage environment is susceptible to deterioration by organisms. Wood deterioration organisms, such as fungus also easily penetrates timber from the cross section. The large cross sections of CLT would be weakness against deterioration by organisms. Therefore, the cross sections of CLT must be considered when evaluating its durability of CLT. To develop the accelerated decay test for CLT regarding with the cross sections, we examined the acceleration of deterioration by contacting untreated CLT samples of the dimension 150×150×150 mm with fungus (Fomitopsis palustris) grown in agar medium in plastic container for 3 and 6 months. As the results, the mass loss of the samples attached with two containers (samples sandwiched between two containers) was higher than of with one container. The mass loss of the samples exposed for 3 months with two containers was lower than that of the samples exposed for 6 months with one container. The method with two containers is considered to be more suitable for the accelerating decay test of CLT.
T Miyauchi, K Kambara, W Ohmura, T Mori, H Matsunaga, N Hattori

Preservative Treatment of CLT: An Example at Shimojishima Airport
2019 - IRG/WP 19-30748
Cross laminated timber (CLT) is a relatively new construction method that allows multi-storey construction using solid wood instead of concrete or steel. It is a method favoured by progressive architects and recognized for its much lower environmental footprint. Wood is an excellent construction material and is a long-term carbon sink that also performs well in the event of earthquakes and fire. Obviously being made of a natural organic material, durability performance against mold and wood destroying organisms is a concern. Even if it were possible to permanently keep the wood dry to prevent wood rotting basidiomycete fungi, some pests are able to attack wood that is wetted temporarily (e.g. mold fungi) or even relatively dry wood (e.g. subterranean termites, wood destroying beetles, dry wood termites and carpenter ants. In most parts of the world there is an active remedial treatment market dealing with decay in structures that were also supposed to be kept dry. In the USA damage caused by decay fungi is thought to be even greater that that caused by subterranean termites (Smith and Whitman 2007). The relatively modern use of indoor plumbing and air conditioning has increased interior moisture issues due to water leaks and condensation. In single family residential construction, when problems occur it is relatively easy to carry out remedial treatment of infested structural wood and wood replacement. Even whole structural subfloors sometimes need replacement due to decay caused by high humidity in conjunction with air conditioning. However, it is NOT easy in multi-storey mass timber construction. For this reason, a global representation of wood scientists has discussed this issue and even signed an open letter on the need to address durability of mass timber construction (Taylor et al. 2016). Countries with subterranean termite problems typically have good standards that address them. Soil poisons, primary barrier wood treatments (to a certain height of the structure) and physical barriers, are well entrenched as control methods (Lloyd et al., 2015). However, none of these methods control the other wood destroying organisms. Wood treatment applied to the bottom ~1 meter of a structure was developed originally in Japan and, with glycol borates, is now the leading commercially applied termite preventive treatment in the USA (to meet the US Department of Housing and Urban Development, State and building code requirements). This can be extended to whole house wood destroying organism control (Lloyd et al., 2015). Possible approaches to address durability include the use of naturally durable wood or pressure treatment of wood with appropriate preservatives. A topical treatment (to avoid significantly re-wetting otherwise dry wood) with a diffusible preservative (to move in the event of enough moisture to support decay) and a moldicide may also be adequate. Such treatments could be carried out by spray, dip or double vacuum application and do not typically cause dimension changes (Jermer & Lloyd, 2000). Borates (especially glycol borates for dry wood e.g. Turner, (2008)) have the advantage of being effective against both decay fungi and insects at low retentions (Lloyd, 1997) and are even bait toxicants against subterranean termites at low retention (e.g. Jones, (1991). Such approaches have been successfully used in residential construction such as under the old German Standard DIN 68-800 where lumber was dipped in a 10% disodium octaborate tetrahydrate solution. The use of an inorganic salt as the active ingredient is also good in topical applications where organic systems can be destroyed by UV light during construction (Lloyd et al., 1998). Even non wood destroying insects such as psocids and cockroaches can be controlled via the use of borate treated wood (Lloyd et al., 2003). Borates have low acute mammalian toxicity are globally available from a number of suppliers. To enhance moldicidal performance there are a number of good active ingredients including quaternary ammonium compounds, carbamates, chlorothalonil, azoles and isothiazolinones. An example of such a treatment includes the Arch/Lonza Frame Guard system commercialized in the USA (Lloyd, 2015). Using topical treatments also has the added advantage of being able to change formulations relatively easily (for example you could use different borate concentrations for geographies with and without subterranean termites) and to ensure that all of the construction components are treated (the mass timber itself but also framing and plywood and many other SKUs that typically go into a building. A 40% disodium octaborate tetrahydrate in glycol formulation (commercially available as Boracare from Nisus Corporation) has performed very well in 10- and 15-year field tests in Mississippi (Williams & Amburgey 2003) and Florida (Barnes et al., 2014) against subterranean termites, in preventive and remedial drywood termite tests (Austin & Gold, 2006; Lewis 2012), and in decay tests such as AWPA E 10 (Amburgey et al., 2004). Formal testing was also carried out in Japan as part of the JWPA approval procedure. In addition, a field test was carried out specifically for the Shimojishima Airport project. A separate series of diffusional penetration and rain exposure leaching tests that we carried out in Japan were also useful. Mitsubishi Estate Co., Ltd. organized the construction which was designed by Nikken Sekkei Ltd. architectural office and built by local contractors for Mitsubishi Estate Co. Ltd. The commercial operations of the Airport are carried out by Shimojishima Airport Management Co. Ltd. Topical treatment was carried out using a 40 % DOT glycol borate diluted at a 1 to 1 volume dilution in water (Boracare to equal a 23 % DOT solution concentration). 0.8 % diecyl dimethyl ammonium chloiride (1% as Moldcare available commercially from Nisus Corporation) was added as a surface moldicide. The diluted material was applied with roller coating at Yamasa Mokuzai Co. Ltd., the CLT manufacturer. An application of 300ml m2 was used in compliance with JWPA requirements to treat 6,000 m3 of CLT. This is a higher concentration and higher application rate than required by US EPA registered label against all non-subterranean termite organisms but was chosen to help drive diffusion over time, to give protection against subterranean termites, to enhance spread of flame performance, and to supply some reservoir to compensate for dilution due to diffusion into the wood. All testing and treatment results went well, and the construction is now complete. The inaugural direct flight from Narita to Shimojishima was March 30th 2019 and many more flights will be able to land in an airport that is effectively storing carbon, and will remain free of drywood termites and other wood destroying organisms for the decades to come. If mass timber and especially CLT is to gain the position it deserves in future construction, it is essential that long term durability is addressed. This project has shown that is relatively easy and cost effective to do so.
J Lloyd, N Yamashita, A Taylor

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