A field test of six millwork preservatives has been ongoing for twenty years, using a simulated window corner, or "Y-joint", as the test unit. Three preservatives provided excellent protection to white pine and white spruce: 5% pentachlorophenol in varsol, phenyl mercury oleate in varsol, and 0.75% oxine copper in varsol.
A field test of six millwork preservatives has been ongoing for 25 years, using a "Y-joint" as the test unit. Three preservatives provided excellent protection to white pine and white spruce: 5% pentachlorophenol in varsol, phenyl mercury oleate in varsol, and 0.75% oxine copper in varsol.
Canadian wood species such as spruce and pine are difficult to treat with wood preservatives or other wood enhancing formulations due to a thin sapwood band and refractory heartwood. One method of improving penetration is by biological incising. Biological incising with Dichomitus squalens was originally developed in Austria in the 1990s to increase the permeability of European spruce prior to treatment with wood preservatives. Recently the patents on this technology lapsed. It was considered unlikely that industrial use of a European white-rot fungus would be acceptable in Canada. FPInnovations therefore conducted a screening test of a range of Canadian isolates of various white-rot fungi to identify an isolate that would be suitable for biological incising of Canadian spruce and pine. Under pure culture conditions, one isolate of Dichomitus squalens isolated from white spruce was found to greatly increase the permeability of the wood, particularly in spruce. The objective of the current study was to determine if these results could be achieved on commercial sized wood under non-sterile conditions more similar to an industrial setting. Lumber samples, 3.8 cm by 8.9 cm by 400 cm in length were incubated in plastic totes with fungal inoculum. Two isolates of fungi were tested as well as two different decontamination methods (steam and Benomyl solution) and two time frames (4 and 6 weeks). Through treatment of spruce samples (19 mm penetration) with 1.7% ACQ was achieved after six weeks incubation with D. squalens 78A (a spruce isolate). In matched samples treated with MCA, a minimum of 10 mm penetration was achieved in 90% of the samples. Strength loss in some individual samples was higher than adjustment factors for conventional incising (over 25%) suggesting that incubation time may need to be shortened. Preservative penetration was more variable in pine but permeability was increased; 60% of the samples reached a minimum penetration of 5 mm. Incubation time and conditions may need to be adjusted to achieve more consistent results. The results of this study show that biological incising can greatly improve the permeability of spruce and pine and can be achieved on 38 by 89 dimension lumber under conditions that could be utilized in an industrial setting. Future work should focus on determining incubation conditions that allow penetration requirements in Canadian standards to be met with acceptable strength loss.
The biggest obstacle to the enhancement of wood properties through any form of chemical treatment is the impermeability of the heartwood of virtually all Canadian Wood species and their relatively narrow sapwood. Incisors using toothed rollers are commonplace in Canadian treating plants but they are not used for many products due to the detrimental effect on surface appearance. Alternative incising technologies anticipated to have less effects on surface appearance have been investigated over the past 30 years. This report revisits four of these technologies, lasers, needles, water jets and biological incising and evaluates their potential for further investigation based on recent advances in technology. Even using the latest technology, laser incising would be too slow and too expensive for a Canadian treating plant. Needle incising would be too slow but the equipment cost should not be an issue. Water jet treatment would also be too slow and the equipment cost is unknown. Biological incising is a very different approach involving batch processing. The major factor would be the cost of inventory which depends on the duration of incubation yet to be determined.
A major constraint to the Canadian wood preservation industry in both domestic and export markets is the difficulty of penetrating Canadian wood species with preservatives. FPInnovations has put considerable effort into various forms of improved mechanical incising but these have not been adopted by the industry due to adverse effects on throughput and appearance of the final product. Recently, work in Europe has shown promising results from biological incising using white-rot fungi that colonize wood relatively rapidly but decay slowly. The use of European isolates of fungi in North America may be constrained by phytosanitary concerns. This report covers an experiment to screen North American isolates of white-rot fungi for potential as biological control agents. A modification of the soil-block test method was used to evaluate the ability of a range of fungi to improve permeability without affecting strength properties. Wood samples were exposed to the fungi for zero, two, four and six week time increments and were then treated with a 1.5% ACQ-D solution. Preservative uptake was calculated based on change in weight before and after treatment. Two isolates of Dichomitus squalens were found that dramatically increased preservative uptake. These samples were tested for strength loss and preservative penetration. Spruce samples exposed to D. squalens isolate 78A for six weeks were completely penetrated with preservative (19 mm depth) in all six samples. D. squalens 78B also showed promising results in pine and spruce samples based on uptake and penetration data. No stiffness loss was detected in any of these samples based on results from the crushing tests.
An accelerated decay test was set up to compare the performance of CCA-treated needle-incised white spruce and lodgepole pine heartwood with end-matched conventionally-incised material. Short lengths of 2 x 4 and comparable untreated material were installed in a warmed soil bed in the open air. After 12 years of accelerated exposure (equivalent to 15 years' natural exposure), all the treated material - spruce and lodgepole pine, needle and conventionally incised - was almost completely sound with minor patches of surface decay. In contrast, both the untreated spruce and the untreated lodgepole pine heartwood had failed due to decay. The performance of needle-incised and conventionally-incised lumber has been very similar in both species.
Preservation - Incising - Tests
Picea - Preservation
Pinus contorta Dougl. var. latifolia - Preservation