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.