In wood products, such as parquetry, cabinetry and furniture, some of the performance criterions are related to moisture transfer between their different construction layers. Non homogenous moisture transfer usually results in the product’s deformation . Engineered Wood Parquet Flooring (EWPF) is an important case, which presents non homogenous moisture transfer due to its utilisation in service. Many types of varnish are available on the market. Physical properties of those varnishes such as hardness and abrasion resistance are readily available from the manufacturers. No data on water vapour diffusion is available, so this study is focused on this specific topic. Water vapour coefficient was determined for 6 commercial and industrial varnishes. These values will be used in further modelling work on EWPF.
Lacking the UV protection provided by copper, carbon-based preservative-treated wood used in many above-ground applications will require coating to meet consumer demand for weather resistance. While earlier metal-based preservatives were true solutions, many of the formulations of carbon-based preservatives rely on surfactants for solubility or dispersion in water. These surfactants can potentially react badly with the dispersion agents in the existing coatings on the market. The present work investigates the performance of six selected coatings on white spruce heartwood and ponderosa pine sapwood untreated and treated with one of three carbon-based preservatives. An earlier report described coating performance after 500 hours of artificial weathering (Stirling and Morris, 2010). The present report describes coating performance after 1000 hours of artificial weathering. The general ratings of the coatings on spruce were typically one to two points higher than those on pine indicating that spruce was a more stable substrate. Contrary to the initial concern, treatment with carbon-based preservatives was associated with coating performance under accelerated UV exposure similar to, or slightly better than, that on untreated wood.
Ultraviolet and visual light can damage wood; so many finishes include chemicals for UV protection. The efficacy of these chemicals depends on a wide variety of factors, but at a fundamental level it is related to their ability to absorb or reflect strongly over a wide range of frequencies. This report describes the use of UV/Visible spectrophotometry to measure the transmittance of light radiation through finishes. The development method was applied to measuring the effects of additives and to comparing commercial finishes.
The goal of this project is to develop an economically, technically and environmentally viable transparent coating that will provide long-term weather protection without masking the natrual colour and texture of wood.
Wood products compete with an increasingly wide range of alternative materials in markets for structural and decorative construction materials. If wood is to retain and expand its market share, it must be able to offer similar low-maintenance performance. It must also be able to capitalize on its natural appearance. Consumer demand for “transparent” coatings can be seen in the degree to which these are commonly used in high-end shop fronts, recreational properties and landscape furniture in resort areas, despite the fact that failed examples of such uses can also be seen everywhere. Failure of transparent coatings in North America occurs after 0.5 to 1.5 years depending on the climate and the degree of exposure.
In previous work, a range of commercial transparent coatings were tested and two variants of one particular water-based coating stood out from the rest. The ultimate failure of this coating in the early testing was primarily from attack by black stain fungi. Thus it was considered important to evaluate alternative fungicides to improve resistance to these organisms. In the first such test (Report #1), unusually favourable conditions for black stain fungi in the first six months of exposure provided some early results. Simply changing from the earlier manufacturer’s recommendation of one coat of step one and one coat of step two, to two coats of step one and one of step two showed improvement in resistance to black stain. One of the modifications to the UV protectant system had a negative effect on resistance to black stain. None of the fungicides tested were more effective in protecting against black stain than IPBC, the fungicide in the commercial formulation. Furthermore a new formula of IPBC was not as effective as the older formula. However, two patterns of black stain were noted and there appeared to be some variation among fungicides in their resistance to these two patterns. This suggested that a combination of IPBC and Propiconazole might be effective in protecting coatings from a broader range of black stain fungi. There were also indications that an “inert” formulation agent used in this pre-treatment was contributing to the performance and this was therefore further investigated.
An accelerated test in a Weather-Ometer (Report #2) showed a UV absorber alone provided substantial protection against the light wavelengths capable of penetrating a water-based transparent urethane over 2000 hrs of artificial weathering. No other UV protectants, when combined with UVA added to this protection. Furthermore, no other UV protectants provided substantial protection against the light wavelengths penetrating a water-based transparent urethane. A damp chamber test showed a combination of propiconazole and IPBC was highly effective in preventing growth of mold and stain.
Report #3 covers the initiation of a test of the second generation of UV protectant pre-treatments and biocide combinations. It also evaluated the apparent beneficial effect of the inert formulating agent. UV protectant combinations were tested under a water-based two-step transparent coating and under a water-based clear exterior urethane. The biocide combinations were used as pre-treatments and incorporated in steps one and two of the water-based two-step transparent coating. After six months’ exposure in Mississippi and Vancouver, all the material in the UV protectant test was rated 7 or higher. There were early indications of deterioration for the controls with Inert B (no UV protectants), for 2.5% HALS and for 7.5% HALS. Most of the downgrading was due to black stain fungi, suggesting the biocide combination and concentration used in this part of the test was inadequate to provide long-term protection. In the biocides test, additional coats of step one provided a substantial beneficial effect on black stain resistance. It was clearly beneficial to have some pre-treatment and it was also clearly important to include the biocides in the coating and not just in the pre-treatment. There were early indications of a positive effect from the incorporation of ZnO with the organic biocides. There was no consistent pattern to allow the effects of Inerts A and B to be distinguished.
Report #4 describes the use of UV/Visible spectrophotometry to measure the transmittance of light radiation through finishes. The developed method was applied to measuring the effects of additives and to comparing commercial finishes.
The objective of this project was to develop an economically, technically and environmentally viable transparent coating that will provide long-term weather protection without masking the natural colour and texture of wood. The project focused on: 1). pre-treatments to prevent degradation of the underlying wood by light wavelengths penetrating transparent coatings; and 2). biocide combinations to extend duration of resistance to black stain fungi. The work done and the reports produced from this work are summarized in this report. Based on a critical review of the literature and the work done in this project over the past six years, the following recommendations can be made to optimize the performance of water-based transparent coatings on wood in exterior vertical applications.
Use heartwood faces
Round all corners
Sand even fresh wood
Pre-treat with an effective biocide combination and a visible light protection system
Selection of a coating virtually opaque to UV light with an optimum combination of water resistance and vapour permeability with water-sheeting surface properties
Coating application to a thickness of 60 microns (2.4 mils).
Commercialisation of a low maintenance transparent coating is expected to assist wood products to maintain residential market share in the face of competing materials and potentially expand markets in recreational property and non-residential applications. Four areas for improvement were identified: optimizing the UV blocking capability of the coating, improving black stain resistance of the coating, improving UV resistance of the underlying wood and improving black stain resistance of the underlying wood. This study focussed on improving UV/visible light resistance of the underlying wood and the effect of the UV protectants on resistance to black stain. Samples of ponderosa pine sapwood were pre-treated with a range of individual compounds with potential as UV protectants and a range of combinations of these compounds. Half of each sample was finished with two coats of the first step and one coat of the second step of a two-step water based transparent coating. The other half was finished with three coats of transparent water based urethane. The first set of samples was exposed for 2000 hours in an Atlas Weather-Ometer®. The weathering cycle was full time UV and full time misting using diffusers over the spray nozzles, except the mist was turned off for one hour each workday. The samples were evaluated using a set of criteria developed by the USDA Forest Products Laboratory at Madison. Comparable samples were pre-treated with the same series of UV protectant systems then one half was finished with two coats of the first step and one coat of the second step of a two-step water based transparent coating. The other half was left unfinished. Four combinations of biocides were added to this part of the experiment. The second set of samples was inoculated with a spore suspension of black stain fungi and exposed for 2000 hours in damp chambers at 20° C. These samples were evaluated for stain intensity on a 0 to 5 scale.
Uncoated samples exposed in the Weather-Ometer showed severe weathering leaving the wood completely white with loose surface cells. Controls with no pre-treatment showed virtually the same level of damage under the water based urethane though the coating itself remained largely in place albeit with considerable cracking. The only individual UV protectant that showed substantial protection against UV under the water based transparent urethane was a UV absorber (UVA), Tinuvin 1130. The two-step transparent water based coating proved so effective at stopping UV that there was no damage to the underlying wood, even for the control with no pre-treatment. It did suffer from discolouration with whitening and blackening in places, types of colour change not seen under normal service conditions. The suggested the constant UV and water may have created conditions conducive to chemical reactions not seen in service such as conversion of transparent iron oxides from iron III to iron II.
None of the other UV protectants combined with the UVA provided any substantial improvement to its performance. Several of the UV protectants had adverse effects on performance. The colloidal zinc oxide caused blistering of the water based transparent urethane. The trans iron oxides turned black possibly due to reduction from iron III to iron II. Lignostab caused a yellow discolouration of the water-based transparent urethane in reference samples not exposed to light.
Several of the UV protectants appeared to increase the growth of mold and stain fungi on the samples. All four biocide combinations were very effective at controlling mold and stain fungi. The results of these tests were used to design a field test of UVA and biocide combinations.
More stringent regulations on volatile organic compounds in exterior wood coatings in Canada have prompted many companies to reformulate their products so there is little impartial data available on their medium to long term field performance. Selected commercial semi-transparent penetrating stains were evaluated in a field test after six months of exposure in Maple Ridge, British Columbia. All coatings exhibited some colour change and degradation; however, additional exposure time is needed to differentiate product performance.
Le bois exposé à des conditions extérieures sur lequel on a appliqué un traitement de finition devient, en quelques années seulement, inutilisable s’il n’est pas efficacement protégé des ultraviolets et de l’humidité. Lorsque le bois est exposé aux intempéries, la conformité du traitement de finition est particulièrement déterminante, ce traitement constituant la principale défense contre les conditions atmosphériques. Par ailleurs, on observe une croissance de la demande des consommateurs à l’égard de la durabilité, du faible coût de l’entretien et, dans certains cas, de la préservation de l’aspect naturel du bois.
Le bois traité adéquatement et exposé à des conditions extérieures peut durer fort longtemps. Les produits de finition au latex, entre autres, sont efficaces pendant dix ans ou plus. Par contre, s’il n’a pas été traité adéquatement, le bois s’écaille, se fissure, s’érode ou se décolore après seulement un an d’exposition. La durabilité du traitement de finition est tributaire de divers facteurs, les plus importants étant les conditions d’utilisation, les propriétés du substrat du bois et le type de traitement. Pour maximiser le rendement du bois utilisé à l’extérieur, il est essentiel de bien comprendre la nature de ces facteurs et leur interrelation.