A transparent coating with long-term performance could help wood maintain its share of residential markets against material substitution and potentially expand markets in recreational property and non-residential buildings. While transparent coatings can be made reasonably resistant to UV some UV likely penetrates to the wood and by necessity clear coatings are transparent to visible light. Visible light can also cause damage over the long term thus the underlying wood needs additional protection. Four novel UV protection systems were tested as pre-treatments on uncoated wood and under three coatings, a water-based film forming coating, a water-based acrylic varnish and a solvent based water repellent. Samples were exposed to natural weathering facing South at 45° at a test site in Gulfport, Mississippi, in collaboration with the USDA Forest Products Laboratory. The test material was inspected every six months for discolouration, mold and stain, coating water repellency, flaking, erosion and cracking and substrate condition. After 24 months exposure, coatings over the combination of UV absorber and lignin stabilizer identified by Stephen Ayer were performing better than the same coatings applied over the combination recommended by Ciba and coatings over both pre-treatments were performing substantially better than controls with no pre-treatment. Projection of fitted curves beyond the data appears to indicate that pretreatment may double the life expectancy of the coating. There was no consistent effect of the synergists on either combination at this time.
Three Gram negative bacteria isolated from brownstained western hemlock were investigated for their capacity to produce hemlock brownstain. Brownstain was observed when infecting western hemlock with two bacteria. Oxygen was strongly indicated as being indespensable for the development of brownstain in infected samples. However, pH did not seem to influence the production of this stain.
In this study builders and professional repair and remodellers were given a chance to evaluate 12 of the most common home siding products available in the market today. The products were evaluated on seven different attributes: price, maintenance, installation, attractiveness, status/image, fire resistance, and durability. Overall, fire resistance, attractiveness, and maintenance were selected as the most important product attributes by single-family homebuilders and repair & remodellers. The majority of respondents stated that their customers had a strong influence on their final choice of siding materials. In addition respondents were asked for their opinion regarding product popularity, rate of installation, substitution trends, and their choice of siding products for different categories of homes.
A system which integrates architectural and structural design issues for timber connections will be developed for a limited number of connections and loading conditions which are dealt with in various national and international codes and standards. The scope of engineering issues relevant to connections will be expanded to include a wide range of timber connections and engineering solutions which are not covered by code procedures. This will include cases such as 3-dimensional loading configurations, dynamic analysis of connections and more rigorous analysis procedures. Progress on these objectives is described.
This study relates to technology for tailor-making PF resin with molecular weight and size distributions beyond those now available for commercial processing. Consequently, adhesive mobility and cure speed can be adjusted through use of a two-component resin system comprised of continuous and dispersed phases. Current studies specifically concern two-component alkaline plywood formulations suitable for bonding veneer at 12 plus or minus 2% m.c.
The objectives of this study were to produce and modify phenolic dispersion based adhesives using technology recently developed at Forintek and to further characterize the physical properties and bonding properties of these systems for veneer and composite board applications with emphasis on faster cure speed potential. Data developed in this study indicate opportunities to improve waferboard and plywood PF adhesives in terms of color, cure rate and application properties. Further research work is recommended to improve techniques for producing and characterizing appropriate powder disperson-like formulations for wood bonding.
Further data on flow, viscosity-solids and veneer bonding at dry and 11 plus or minus 2% wood m.c. conditions are provided for heated PF powder systems. This information is intended to supplement the main report issued in March 1987.
This study aims at assessing the changes happening within the residential construction industry with respect to walls. There are three major goals of this study. The first is to assess the attributes demanded by builders in single family wall products and systems. The second is to assess product usage and substitution in single-family walls. The third aim is to assess the move to component building in residential walls.
A mail out survey was sent to single-family homebuilders in the US, one randomly drawn list of builders plus a list of the top 100 builders in the country. The survey covered builders concerns, attributes demanded in walls, and products and systems used for walls.
Results indicated that energy codes were the top concern of builders. Interestingly, very few builders were concerned with engineered wood or prefabricated systems availability, but lumber availability was considered a constraint by some firms, especially the large ones.
With respect to walls attributes it is clear that the most important attribute of a wall is straightness and square. However, the next three most important attributes are related to on-site issues; speed of assembly, easy to handle, and low on-site waste. This was especially true for large builders. Cost factored in as moderately important with installed cost finishing ahead of material cost.
With respect to walls systems it was found that over 40% of builders have tried prefabricated wood walls. This was strongest in the North. Large builders also were high users of prefabricated wood walls. Prefabricated exterior walls were more common than prefabricated interior walls. Many builders, especially those in the West, used site-built steel for interior walls. In fact, it would appear that of the prefabricated wood interior walls and site-built steel are substitutes.
Labour availability is an equal, if not greater, factor than product availability in the competition among building products and systems for residential construction today. Further, demographic forecasts show labour availability decreasing into the future. At the same time the consolidation of residential building firms is giving rise to more automation and off-site building. For these reasons, it is safe to assume that prefabricated building will only increase into the future. Therefore, it is imperative that the wood products industry defines how the competitive advantage their products have always had in the residential construction industry can be adapted and maintained in an era of prefabricated construction.
Wood failure evaluation is the key criterion for predicting the long-term durability of plywood. At present, the conventional visual method for plywood wood failure evaluation is slow and subjective. Even experienced evaluators can show significant differences in their evaluations on the same plywood specimen and an individual evaluator can make different wood failure estimates on the same specimen at different times. Differences among evaluators can be as high as 50% for some samples. Evaluations can be influenced by room lighting, the wood species, sample treatment, and readings from prior samples. An automatic wood failure evaluation system using image analysis techniques could potentially be programmed to consider all the variables and respond with consistent wood failure values regardless of the experience level of the machine operator. This report describes the results of a one-year project in which a system for automatic plywood wood failure determination was investigated. A color optical imaging system was assembled and the preliminary work of compiling suitable algorithms was completed with promising results. The imaging system was 100% effective in reproducing individual sample values. Samples were sorted according to plywood type and test method to develop appropriate program algorithms for each category. The wood failure program was then further developed to automatically detect wood species and test method, thus avoiding the need for specimen separation prior to evaluation. Based on nearly 1200 samples in four categories, the differences in average values of wood failure between human evaluation and machine vision were found to be less than plus or minus 5%. In addition, a minimum of 85% of individual machine readings fell in the plus or minus 15% range of deviation expected of human wood failure readers. The imaging system was more accurate for light-colored specimens (i.e., Canadian Softwood Plywood) than darker-colored specimens (i.e., Douglas fir ) and for specimens where resin had been applied by spray. In order to make the imaging system more reliable and robust, the algorithm parameters now need to be fine-tuned based on a larger sample database.