Building high energy efficiency has become a must to reduce carbon emission from the built environment and to meet needs of consumers. Industrialized construction provides an effective way to produce highly insulated and airtight building envelopes to achieve superior building performance, such as Net Zero Energy. However, it is important that as other attributes (e.g., seismic, wind, fire, vibration, etc.) are being addressed, further research is needed to develop well rounded building envelope solutions. Meanwhile, improvement may be made in automated production equipment and software to optimize and monetize these solutions.
The purpose of this study is to investigate and record the principal problems associated with chipped surface quality at canter lines and evaluate degrade and value losses due to these problems.
Mill measurements were conducted in five member sawmills in British Columbia to evaluate the value losses and lumber degrades due to chipped surface defects. The test lumber was sampled from the planing mills to identify the chipping losses and main problems. The five types of chipped surface defects influencing lumber grade are: knot tear-out; failure to remove chipped spline channel; torn grain without knots; scalloping; and chipped thin end.
Average value losses for all mills were $11.4/MBF and $12.6/MBF in freezing and non-freezing conditions respectively. Removing the non-freezing data from one mill changed this to $11.4/MBF and $9.0/MBF respectively. Knot tear out caused 60% of lumber to be degraded. On average, over 55% of knots had tear-out. 42.3% of trim length was caused by failure to remove chipped spline channel.
This literature review aims to provide a general picture of retrofit needs, markets, and commonly used strategies and measures to reduce building energy consumption, and is primarily focused on energy retrofit of the building envelope. Improving airtightness and thermal performance are the two key aspects for improving energy performance of the building envelope and subsequently reducing the energy required for space heating or cooling. This report focuses on the retrofit of single family houses and wood-frame buildings and covers potential use of wood-based systems in retrofitting the building envelope of concrete and steel buildings.
Air sealing is typically the first step and also one of the most cost-effective measures to improving energy performance of the building envelope. Airtightness can be achieved through sealing gaps in the existing air barrier, such as polyethylene or drywall, depending on the air barrier approach; or often more effectively, through installing a new air barrier, such as an airtight exterior sheathing membrane or continuous exterior insulation during retrofit. Interface detailing is always important to achieve continuity and effectiveness of an air barrier. For an airtight building, mechanical ventilation is needed to ensure good indoor air quality and heat recovery ventilators are typically required for an energy efficient building.
Improving thermal resistance of the building envelope is the other key strategy to improve building energy efficiency during retrofit. This can be achieved by: 1. blowing or injecting insulation into an existing wall or a roof; 2. building extra framing, for example, by creating double-stud exterior walls to accommodate more thermal insulation; or, 3. by installing continuous insulation, typically on the exterior. Adding exterior insulation is a major solution to improving thermal performance of the building envelope, particularly for large buildings. When highly insulated building envelope assemblies are built, more attention is required to ensure good moisture performance. An increased level of thermal insulation generally increases moisture risk due to increased vapour condensation potential but reduced drying ability. Adding exterior insulation can make exterior structural components warmer and consequently reduce vapour condensation risk in a heating climate. However, the vapour permeance of exterior insulation may also affect the drying ability and should be taken into account in design.
Overall energy retrofit remains a tremendous potential market since the majority of existing buildings were built prior to implementation of any energy requirement and have large room available for improving energy performance. However, significant barriers exist, mostly associated with retrofit cost. Improving energy performance of the building envelope typically has a long payback time depending on the building, climate, target performance, and measures taken. Use of wood-based products during energy retrofit also needs to be further identified and developed.
Potential market gain for Canadian softwood plywood in residential construction could arise from the emerging Chinese market to build massive numbers of affordable apartments and the upcoming rebuilding effort in Japan following the earthquake and tsunami disaster. Compared to the main Chinese species (poplar), common BC species, such as Douglas-fir, spruce and hem-fir, have competitive advantages in the aspects of log diameter, wood properties and veneer quality and processing productivity. For non-residential construction, Canadian plywood concrete forms also offer competitive advantages over Chinese overlaid poplar counterparts due to their higher stiffness and strength. However, the production cost has to be kept to below US$ 500/m3 for a profit margin. Further, three-ply and four-ply Canadian softwood plywood panels are ideally suited for the base materials of multi-layer composite floor, which currently is gaining momentum in China and other countries.
A sizeable increase in industrial and remodelling market is anticipated for the Canadian plywood industry. This will be mainly driven by a number of specialty plywood products, such as container floor and pallet, light truck, utility vehicle, trailer and camper manufacturing. However, these products are not commonly manufactured by larger commodity manufacturers in Canada. China is currently the largest global supplier of container floors, most of which are made from imported plywood, bamboo and poplar veneer. To meet their stringent requirements and gain a market share, Canadian plywood industry should take appropriate actions in adjusting veneer thickness, veneer grade, veneer treatment, and panel lay-up.
Japan has developed customized products such as oversized plywood for wall applications, and termite/mould resistant plywood for above ground and ground-contact applications. China has developed numerous new value-added veneer products for niche markets. Such products include marine plywood, sound reducing plywood, non-slip plywood, metal faced plywood, curved plywood and medium density fiberboard (MDF) or particleboard (PB)-faced plywood.
In order to stay competitive in the global market, Canadian plywood industry needs to:
remove the trade constraints between softwood plywood and hardwood plywood,
remove in-plant manufacturing barriers to deal with both softwood and hardwood processing,
diversify products for both appearance and structural based applications, and
develop new value-added products for niche markets.
This study suggests the following opportunities for Canadian plywood producers to
incorporate naturally decay-resistant species such as cedar as surface veneer and/or perform veneer or glueline treatment to make marine and exterior plywood for improved durability,
characterize veneer properties from the changing resource for better utilization,
peel some thinner and higher quality veneer for making specialty plywood,
conduct stress grading in combination with visual grading to maximize value recovery from the available resource,
increase the flexibility of panel lay-up for domestic/overseas markets and various applications,
develop mixed species plywood by mixing available hardwood species such as birch, maple, alder, aspen veneer (as overlay materials) with softwood plywood to achieve better appearance and higher performance,
develop new structural composite lumber (SCL) products such as veneer strand lumber (VSL) from low quality logs, particularly beetle-killed, and random veneer or waste veneer,
develop new drying, pressing and adhesive technologies for processing high moisture veneer, particularly hem-fir and spruce, to improve productivity and bond quality and reduce panel delamination,
develop light weight and strong hybrid plywood panels for furniture applications, by adding MDF or PB on the face of plywood,
develop hybrid plywood for floor applications to reduce thickness swell and increase dimensional stability and stiffness,
develop hybrid cross-laminated timber (CLT) panels from lumber, plywood and laminated veneer lumber (LVL) for low- and mid-rise residential and non-residential applications, and
develop a series of new product standards for specialty plywood.
A market research study for each product opportunity is recommended to develop a solid business case for each.
Delamination currently accounts for approximately 85% of customer complaints about plywood as a sub-flooring product. It has become an urgent issue to many of our plywood members. It is estimated that by merely reducing 1% delamination in a 250 million ft2 (3/8 –in basis) plywood mill, the potential annual savings will be approximately $650,000. To help reduce plywood delamination, the key objective of this project was to develop a generic best practice checklist as a guide for manufacturing plywood.
A generic best practice checklist for manufacturing plywood was compiled with a focus on the following four key checkpoints: veneer peeling, veneer drying, panel gluing/lay-up and hot pressing. Key process variables at each checkpoint were determined as follows: peeling related veneer surface roughness and thickness variation, drying related veneer moisture content (MC) variation and surface inactivation, veneer temperature, glue coverage and dryout, and pressing time and pressure. Some technical issues were proposed to revisit as a strategy to reduce panel delamination. Among them include optimal lathe bar gap and pitch profiles, and proper knife sharpening for peeling, reduction of veneer overdry during drying, real-time adjustment of glue spread for adequate glue coverage, and use of optimum pressing time/pressure for adequate level of panel compression and glue curing. The resulting generic checklist can be modified for individual mill use.
Through literature review, pilot plant tests, and mill trials, the main causes of panel delamination were identified as: 1) glue dryout from long assembly time and high veneer temperature; 2) low panel compression, light glue spread or glue skips due to rough veneer; 3) little glue transfer due to veneer surface inactivation; 4) inadequate glue cure due to heavy glue spread, overwet veneer, sap wet spots, and short pressing time; and 5) combined effects of the above. It was found that veneer surface roughness had a significant effect on plywood gluebond quality, and excessive roughness and combined effect of veneer roughness, overdry, and glue dryout, were key causes of the low percentage wood failure. A statistical model was also developed from mill trials to predict the percentage wood failure in terms of veneer temperature, open assembly time and glue spread. The model helps establish an operating window for each key variable and adjust the gluing/layup process to reduce glue dryout. Furthermore, a practical method was developed to determine the optimum pressing parameters to achieve target gluebond quality while minimizing plywood thickness loss.
Oriented strand board (OSB) is widely used in house construction in North America. In Canada, OSB panels are commonly made of aspen strands and are susceptible to mould and decay when they get wet. Building envelope failures due to mould, decay or poor construction practices can negatively impact the image of wood. This can lead to product substitution that in turn can affect the wood industry’s overall competitiveness. To ensure durability of OSB panels, the most important consideration is the use of mould- and decay-resistant panels to prevent fungal attack. Using low environmental impact technology to improve the durability of OSB products could have market-related advantages over using chemical protection products. This project aimed to develop technologies for protecting OSB raw materials from biodegradation and to explore biological pre- or post-treatments to increase the durability of panels so they would better resist mould, stain and decay.
The project was divided into three parts. Part one involved developing a biological technology to protect OSB raw materials from biodegradation. In this part, aspen, red maple and yellow birch trees, which are commonly used to make OSB in Canada, were felled in May and cut into 4-foot logs. These logs were then equally divided into two groups (16 logs each) with one group keeping its bark and the other having it removed. These debarked and “bark-on” logs were further divided into two groups, each containing 8 logs. One group of logs was treated with a bioprotectant and another group served as a control. The treated and untreated logs were stored separately in Forintek’s yard. Two inspections were conducted, one at the end of the growth season (in October after a 5-month storage period) and the other after one year. During each inspection, four logs from each test group were examined for fungal degradation (mould, stain and decay), and then cut into strands to be used for manufacturing panels. The panels’ physical and mechanical properties and mould resistance were evaluated.
The second part involved developing a biological pre- or post-treatment technology by using naturally resistant wood species to increase the durability of panels so they would better resist mould, stain and decay. In this part, a series of tests were conducted using various wood species. These tests included a) determining the antifungal properties of bark from various wood species; b) using white cedar to improve panel durability; c) optimizing manufacturing conditions for producing durable panels with white cedar; d) using other wood species to produce mould-resistant panels; and e) post-treating panels with extracts of durable wood species.
The third part consists of developing a biological pre- or post-treatment technology by using fungal antagonists to increase the durability of panels against mould, stain and decay. This part will be conducted in the 2004-2005 fiscal year, and results will be included in next year’s report.
The results of the first part on the protection of raw materials showed that all untreated logs, with or without bark, were seriously degraded by moulds, stain and decay fungi after a summer storage period of five months. The logs with bark were more degraded than the debarked logs, and the log ends were more degraded than the middle sections. After summer storage, 55% to 83% of the wood was degraded in untreated logs. The biological treatment was effective, only 4% to 16% of the wood in treated logs was affected by various fungi after a five-month storage period. Furthermore, the biological treatment was more effective on logs without bark than logs with bark, and more effective on yellow birch and aspen than on red maple. After one year in storage, the total infection rates of untreated logs ranged from 68% to 91%, whereas the rate for biologically treated logs ranged from 27% to 49%. Among these treated logs, the logs ends were degraded from 31% to 62%, whereas the middle sections were degraded from 7% to 26%. Strands cut from untreated logs contained 50% to 75% of grey or blue stained strands, whereas those cut from biologically treated logs contained 10% to 25% of such strands. Panels made using biologically treated logs had the lowest TS and WA values compared with panels made using fresh-cut logs and untreated stored logs. The other physical and mechanical properties of the various panels made for this test were comparable.
The antifungal properties of bark from six wood species (aspen, red maple, yellow birch, balsam fir, white spruce and white cedar) were investigated in the second part of this research project. Based on the colony growth rate of moulds, stain and decay fungi on bark-extract-agar media, white spruce bark was the best at inhibiting growth of these fungi, followed by red maple bark. White cedar and balsam fir bark somewhat inhibited certain fungi tested. Aspen and yellow birch bark did little or nothing at all to inhibit fungal growth. The research also showed that the white cedar heartwood-extract-agar medium not only inhibited decay fungi growth, but also inhibited the growth of moulds and staining fungi. The bark-extract-agar medium of this wood species was less effective in inhibiting fungal growth than the heartwood was.
Three-layer panels made using white cedar heartwood strands in the face layers and aspen strands in the core layer at a ratio of 25:0:25 were mould and decay resistant, but the panels “blew” easily during manufacturing and their mechanical properties were not satisfying. The overall mould infection rate on white cedar heartwood-faced panels was 0.8, which indicated that the panel was mould resistant. White spruce heartwood-faced panels were highly mould resistant and moderately decay resistant. The overall mould infection rate on white spruce heartwood-faced panels was only 0.2 after 8 weeks of exposure to high humidity environmental conditions. In addition to being mould resistant, white spruce heartwood-faced aspen panels also had better IB, MOR and MOE properties, compared with aspen panels. The panels with black spruce in surface layer had mechanical and mould-resistance properties that were similar to those with white spruce in surface. The panels with surface layer of Eastern larch heartwood were non-resistant to moulds and slightly resistant to decay, but they had better IB, TS and WA properties compared with the other types of panels. The overall mould infection rate on the panel with surface layer of Eastern larch heartwood was 3.7, which was similar to the rate for aspen control panels. Aspen panels (serving as control panels) were seriously affected by moulds with overall mould infection rates ranging from 3.8 to 4.9.
Aspen panels with surface layer from whole-wood strands (using both sapwood and heartwood) from white cedar, in a ratio of 25:50:25 and pressed at 220°C for 150 seconds, were well bonded and had IB, TS, WA and MOE values that were similar to those of aspen control panel, but with a higher MOR. All the panels’ properties met the requirements of the standard. This type of panel also was the least infected by moulds, especially in the face layers which rated a 0.2. The panel sides were moderately infected, rating a 2.6, this occurring mostly in the middle layer of aspen strands. The overall rate of this type of panel was 1.0, which indicated that the panels were resistant to mould infection. This type of panel was also highly resistant to brown rot and moderately resistant to white rot.
Panels made of steam-treated white cedar whole-wood strands and aspen strands at a ratio of 3:7 based on oven-dry weight also had low infection rates: the average face infection rate was 1.2; the side infection was 2.4 and the overall rate was 1.6. Compared with aspen panels, this type of panel also had high MOR and MOE values and low TS and WA values.
In the case of white cedar whole-wood strands faced aspen panels, when the pressing time was increased from 160 seconds to 180 seconds at 200°C, the panels’ IB strength and MOE increased whereas the panels’ TS, WA and MOR decreased. By increasing the pressing temperature from 200°C to 240°C and pressing for 160 seconds, the panels’ IB strength, MOR and MOE increased and the panels’ TS and WA decreased sharply. At a pressing temperature of 240°C and a pressing time of 180 seconds, the panels’ IB strength, MOR and MOE increased significantly and the panels’ TS and WA decreased significantly. These data showed that aspen panels with surface layer from white cedar whole strands at a ratio of 25:50:25 and pressed at 240°C for 180 seconds had the best mechanical and physical properties. All panel samples were slightly infected by moulds on the faces. A fair amount of mould occurred on the sides of panels pressed at 200°C for 160 seconds and 180 seconds and those pressed at 240°C for 180 seconds. The panels pressed at 240°C for 160 seconds were the least infected by mould (with an infection rate of 0.3). Panels pressed at 200°C had a white-yellowish colour, whereas those pressed at 240°C were yellow-brownish and darker than those pressed at 200°C. Panels pressed at 200°C for 160 or 180 seconds and those pressed at 240°C for 160 seconds were highly decay resistant, especially to brown rot. The decay resistance of panels pressed at 240°C for 180 seconds was lower compared with the other panels.
Compared with aspen panels, panels with surface layer from steam-treated white cedar strands and aspen strands at a ratio of 7:3 based on oven-dry weight had higher TS, WA, MOR and MOE values and a similar IB value. Panels with surface layer from steam-treated white cedar strands and aspen strands at a ratio of 4:6 based on oven-dry weight had the highest IB value. A reduction in mould and decay resistance corresponded to a reduction in the proportion of white cedar strands in the face layers. The overall mould growth rate was 1.27 on panels with surface layer from steam-treated white cedar strands and aspen strands at a ratio of 4:6, 0.6 on panels with surface layer from steam-treated white cedar strands and aspen strands at a ratio of 7:3, and 0.4 on panels faced with 100% white cedar whole strands, respectively.
Panels made from 100% white cedar whole-wood strands or a mixture of whole-wood strands of white cedar and aspen (50:50) in the core layer were “blown” after pressing. Panels made from a mixture of white cedar and aspen strands at a ratio of 25:75 in the core layer and aspen strands in the face layers had superior IB, MOR and MOE values than other panels. However, their TS and WA values were also higher than those of white cedar-faced panels. Panels made from a mixture of white cedar and aspen strands at a ratio of 25:75 in the core layer and white cedar strands in the face layers had the worst physical and mechanical properties among all the panels made for this test. The tests results for mould showed that panels made with a mixture of white cedar and aspen strands at a ratio of 25:75 in the core layer and aspen strands in the face layers ware seriously attacked by moulds and had an overall mould growth rate of 4.2. No mould infection was found on panels made from 100% white cedar strands. Panels made from a strand mixture of white cedar (50%) and aspen (50%) in the core layer and white cedar strands in the face layers had little mould infection. The overall mould growth rate on this type of panel was 0.2.
Compared with the control aspen panels, aspen panels with surface layer from white cedar whole-wood strands at a ratio of 15:70:15 had similar IB and TS values, a lower WA value and higher MOR and MOE values. When the white cedar strand proportion in the face layer was increased from 15% to 25%, the panels’ IB strength and WA decreased, but their MOR and MOE values increased. Panels with surface layer from white cedar strands at a ratio of 15:70:15 had little infection from moulds on the face and bottom layers, but had an increased infection rate on all four sides. The average overall infection rate of this type of panel was 0.5. When the white cedar in the panels’ face layer was increased from 15% to 25%, the average infection rate on the panels’ faces was still 0.1, but the infection rate of the panels’ sides dropped from 1.2 to 1.0. The overall rate was 0.4. In terms of decay resistance, panels with surface layer from 25% white cedar strands performed better than those with surface layer from 15% white cedar.
This project aimed to develop technologies for protecting OSB raw materials from biodegradation and to explore biological pre- or post-treatments to increase the durability of panels so they would better resist mould, stain and decay. The project was conducted in five parts. Part one involved developing a biological technology to protect OSB raw materials from biodegradation. The results of this part of the work showed that all untreated logs, with or without bark, were seriously degraded by moulds, stain and decay fungi after a summer storage period of five months. The logs with bark were more degraded than the debarked logs, and the log ends were more degraded than the middle sections. After summer storage, 55% to 83% of the wood was degraded in untreated logs. The biological treatment was effective, only 4% to 16% of the wood in treated logs was infected by various fungi after a five-month storage period. Furthermore, the biological treatment was more effective on logs without bark than logs with bark, and more effective on yellow birch and aspen than on red maple. After one year in storage, the total infection rates of untreated logs ranged from 68% to 91%, whereas the rate for biologically treated logs ranged from 27% to 49%. Strands cut from untreated logs contained 50% to 75% of grey or blue stained strands, whereas those cut from biologically treated logs contained 10% to 25% of such strands. Panels made using biologically treated logs had the lowest thickness swelling (TS) and water absorption (WA) values compared with panels made using fresh-cut logs and untreated stored logs. The other physical and mechanical properties of the various panels made for this test were comparable. For the mould resistance, all panels made from fungal treated logs had better mould resistance than those made from freshly cut and untreated logs. Panels made of strands cut from fungal treated debarked logs had better mould resistance than the panels made from fungal treated bark-on logs.
The second part of the research consisted of investigating antifungal properties of barks from various wood species. In this part, antifungal properties of barks from 6 wood species: aspen, red maple, yellow birch, balsam fir, white spruce and white cedar were screened in a laboratory test against moulds, staining fungi, white-rot and brown-rot fungi. Based on the colony growth rate of moulds, stain and decay fungi on bark-extract-agar media, white spruce bark was the best at inhibiting growth of these fungi, followed by red maple bark. White cedar and balsam fir bark somewhat inhibited certain fungi tested. Aspen and yellow birch bark did little or nothing at all to inhibit fungal growth.
The third part involved developing a biological treatment technology by using naturally resistant wood species to increase the durability of panels so they would better resist mould, stain and decay. In this part, a series of tests were conducted using various wood species. These tests included a) using white cedar to improve panel durability; b) optimizing manufacturing conditions for producing durable panels with white cedar; and c) using other wood species to produce mould-resistant panels. The results showed that three-layer panels made using white cedar strands in the face layers and aspen strands in the core layer at different ratios were mould and decay resistant. White spruce heartwood-faced panels were highly mould resistant and moderately decay resistant. In addition to being mould resistant, white spruce heartwood-faced aspen panels also had better internal bond (IB), modulus of rupture (MOR) and modulus of elasticity (MOE) properties, compared with aspen panels. The panels with black spruce in surface layer had mechanical and mould-resistance properties that were similar to those with white spruce in surface. The panels with surface layer of Eastern larch heartwood were non-resistant to moulds and slightly resistant to decay, but they had better IB, TS and WA properties compared with the other types of panels.
The fourth part of the research consisted of developing a biological treatment technology by using fungal antagonists to increase the durability of panels against mould, stain and decay. In this part, two major tests were conducted using various fungal species. They were: a) treating wood strands with three antagonistic fungi, Gliocladium roseum, Phaeotheca dimorphospora and Ceratocystis resinifera, to increase OSB panel durability; and b) treating wood strands with a lignin-degrading fungus, Coriolus hirsutus, to reduce OSB resin usage. The results of this part of the work showed that all of the 4 fungal species used grew well on aspen strands in four weeks, and strands in all treatments had normal wood color after incubation. For IB property, panels made of fungal treated strands were better or similar to the control panels. Panels made of fungal treated strands had higher TS and WA values than untreated control panels. For mechanical properties, panels made of fungal treated strands had a slight lower dry MOR and higher wet MOR than control panels. For mould resistance, panels made of fungal treated strands were infected by moulds one week later than the untreated control panels, and reduction of mould infection rates was detected on fungal treated panels within 6 weeks. After 6 weeks, all panels, treated or untreated, were seriously infected by moulds. Reducing resin usage in fungal treated panels did not affect panel density. Compared with untreated control panels, the IB property of panels made of fungal treated strands was slightly increased by using normal dosage of resin or a reduced dosage by 15%, but slightly decreased with a resin reduction by 30%. There was a negative linear correlation of the panel TS and WA properties with resin reduction by using fungal treated strands. For the mechanical properties, panels made of fungal treated strands had lower dry MOR and MOE values, but higher wet MOR values (except for a resin reduction of 30%) than panels made of untreated strands.
The fifth part involved protecting OSB against mould and decay by post-treatment of panels with natural extracts from durable wood species and from fungal antagonists. In this part, three tests were conducted using extracts of white cedar heartwood and extracts of a fungal antagonist. These tests were: a) screening antifungal properties of natural extracts against mould and decay fungi; b) post-treating OSB panels with white cedar heartwood extracts and finishing coats; and c) post-treating OSB panels with fungal metabolites. The results of this part of the work showed that the mycelial growth of all fungi tested (moulds, staining fungi, white-rot and brown-rot fungi) was inhibited by the extracts of white cedar heartwood and extracts of the fungal antagonist, P. dimorphospora, on agar plates. Panel samples dipped with the cedar extracts got slight mould growth on the 2 faces and moderate mould growth on the 4 sides, whereas the panel samples dip-treated with the fungal extracts got the minimal mould infection among the panels tested. The results of the mould test on the post-treated panels with extracts of white cedar heartwood and three coating products showed that slight or no mould growth was detected on any sample dip-treated with the extracts and then brushed with finishing coats. The decay test showed that most post-treated samples had less weight losses than untreated control samples.
A study was conducted with the primary objective of examining the efficacy of a standard block shear test method to assess the bond quality of cross-laminated timber (CLT) products. The secondary objective was to examine the effect of pressure and adhesive type on the block shear properties of CLT panels. The wood material used for the CLT samples was Select grade nominal 25 x 152-mm (1 x 6-inch) Hem-Fir. Three adhesive types were evaluated under two test conditions: dry and vacuum-pressure-dry (VPD), the latter as described in CSA standard O112.10. Shear strength and wood failure were evaluated for each test condition.
Among the four properties evaluated (dry and VPD shear strength, and dry and VPD wood failure), only the VPD wood failure showed consistency in assessing the bond quality of the CLT panels in terms of the factors (pressure and adhesive type) evaluated. Adhesive type had a strong effect on VPD wood failure. The different performance levels of the three adhesives were useful in providing insights into how the VPD block shear wood failure test responds to significant changes in CLT manufacturing parameters. The pressure used in fabricating the CLT panels showed a strong effect on VPD wood failure as demonstrated for one of the adhesives. VPD wood failure decreased with decreasing pressure. Although dry shear wood failure was able to detect the effect of pressure, it failed to detect the effect of adhesive type on the bond quality of the CLT panels.
These results provide support as to the effectiveness of the VPD block shear wood failure test in assessing the bond quality of CLT panels. The VPD conditioning treatment was able to identify poor bondline manufacturing conditions by observed changes in the mode of failure, which is also considered an indication of wood-adhesive bond durability. These results corroborate those obtained from the delamination test conducted in a previous study (Casilla et al. 2011).
Along with the delamination test proposed in an earlier report, the VPD block shear wood failure can be used to assess the CLT bond quality. Although promising, more testing is needed to assess whether the VPD block shear wood failure can be used in lieu of the delamination test. The other properties studied (shear strength and dry wood failure), however, were not found to be useful in consistently assessing bond line manufacturing quality.