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.
Due to its leachability, Japanese authorities deem disodium octaborate tetrahydrate (DOT) unsuitable for use as a preservative treatment for sill plates. Although the sill plates are not in direct ground contact, and are usually protected from the elements by siding, some authorities suggest that the preservative will diffuse into the damp concrete sill, or that condensation or occasional flooding will compromise the treatment. Due to a lack of data on the extent of boron loss under these circumstances, a test was designed to investigate borate losses from DOT-treated sill plates. This project set up sill plates on wet sills under conditions of high humidity/light condensation, with and without a sill gasket, and with and without water spray (simulating extreme condensation) or occasional flooding.
End-matched samples of DOT-treated 105mm squares were prepared and analyzed for the penetration and retention of preservative. Each sample was placed on a concrete sill contained in polyethylene containers and kept at high humidity (100% relative humidity) with light condensation occurring. A controlled water spray was applied to two sets of test samples. In another set the samples were individually flooded in a separate container for 24 hours once each month. Weighing the samples and analyzing the water for borate content enabled monitoring of moisture uptake and loss of borate over a six-month period. Following completion of the six-month test, the moisture content, preservative penetration, and preservative retention of the test samples were again determined.
The test with high humidity and light condensation alone gave conditions which resulted in sill plates comparable to the wettest sill plates observed in Japanese houses. The data showed that negligible borate leaching occurred from DOT-treated sill plates stored under these conditions. The effect of placing a gasket between the sill plate and the sill could therefore not be determined because of the negligible loss. This work confirmed that significant borate loss only occurred when DOT treated sill plates were washed with large quantities of liquid water, either by spraying or flooding. Spraying resulted in sill plate moisture contents which were double those found in service in older houses in Japan. Modern house construction has dramatically reduced crawlspace moisture contents. Consequently, wetting to this extent would not occur during normal modern house construction and service. The presence of a sill gasket did not stop loss of borate following spraying indicating that the water was dripping off and not passing into the concrete. 2000-2615
The major defining characteristic of lumber cut from trees that have been infected with the mountain pine beetle is the extent of fungal bluestain in the sapwood. Forintek Canada Corp. scientists have previously observed that bluestained wood appears to have different dimensional stability characteristics than non-stained wood when subjected to repeated wetting and drying. Bluestained wood has also been reported to show increased permeability, which may make treatment with liquids such as wood preservatives easier. However, no data is available on how bluestained wood resulting from the beetle attack might affect. We therefore identified the need to generate data on the dimensional stability, checking, and permeability characteristics of bluestained wood compared with non-stained wood.
To examine dimensional stability, specimens of bluestained and non-stained 2 x 4 in. lumber were subjected to wetting/drying cycles. After 5 and 10 cycles, the amount of bow, crook, cupping, twist, and checking was measured. The permeability of the wood was also determined by weighing end-matched specimens before and after a 1-, 4-, and 24-hour dip or after a pressure treatment cycle with chromated copper arsenate preservative, and then calculating the uptake and preservative retention.
The results clearly show that when repeatedly wetted and dried, such as occurs in exterior end uses, bluestained beetle-killed wood is more dimensionally stable (less cupping and twist) and checks less than non-stained sapwood, but is more permeable to water. The stresses appear to be relieved by many micro-checks rather than fewer large checks. Overall, the improved dimensional stability should result in the lumber made from stained wood remaining straighter.
Increased permeability of the bluestained wood was confirmed by data showing enhanced chromated copper arsenate (CCA) uptake and penetration. One implication of the stained sapwood treating more readily than non-stained wood is that in batches of preservative-treated wood, the stained wood is liable to be overtreated or the non-stained wood undertreated. As anticipated, bluestain in the sapwood had no effect on the penetration of preservative into the heartwood, the most refractory part of the wood. Treatment with CCA also masked the bluestain by coloring it green.
The increased permeability probably also has implications for ease of air or kiln drying and possibly reduced degrade in the kiln.
Insects - Attack on trees
Stains - Fungal
Pinus contorta Dougl. var. latifolia - Defects
Preservatives - Permeability
Preservatives - Penetration
Pinus contorta Dougl. var. latifolia - Preservation
This report evaluates a new fluctuating pressure treating process, with a small pressure variation, that could be easily implemented into a treating plant with a control value. Coastal western hemlock being a relatively difficult species to impregnate was chosen as a suitable test species. Incised and unincised hemlock was used to relate to present industry practices.
In the 3-year rotation of subject matter for the reports of the "Durability of Wood" project, attention has again turned to treated commodities. In these tests, we evaluate not only the efficacy of the wood preservative, but also the effect on performance of the quality of treatment that can be achieved with Canadian wood species. The collection of long-term performance data takes time and it is impossible to predict questions about standards for which answers will be needed in 10 or 20 years' time. Consequently, Forintek has maintained a comprehensive field-testing program covering a wide range of commodities, wood species, preservatives and treatment methods. The reports in this compilation cover decking, finger-jointed lumber above ground, shakes, millwork, fence posts, lumber in a termite area and needle-incised lumber in an accelerated ground contact test.
Softwoods - Preservatives
Glued joints - Finger - Preservation
Preservatives - Chromated copper arsenate (CCA)
Preservatives - Penetration
Preservation - Durability
Decking - Preservation
Shingles - Preservation
Thuja plicata - Shingles
Shingles - Durability
Preservatives - Ammoniacal copper arsenate (ACA)
Posts - Preservation
Preservation - Incising - Tests
Picea - Preservation
Pinus contorta Dougl. var. latifolia - Preservation
The recently revived interest in the borate treatment of hem-fir has lead to the search for more rapid treatment processes. Pressure treatment combined with a short diffusion period shows promise, particularly for Pacific silver fir, but further improvements were needed to rapidly achieve penetration of the full cross section in western hemlock. Didecyldimethyl ammonium chloride (DDAC) had been added as a mould inhibitor during the diffusion process but it might also have an effect on uptake through action as a surfactant. End-matched specimens of 105 x 105 mm cut from hemlock baby squares were treated with Tim-Bor to which various concentrations of DDAC were added. Addition of 0.5% DDAC substantially increased the penetration of borate into hem-fir during pressure treatment. Concentrations as low as 0.05% DDAC improved penetration during storage after treatment. A second experiment confirmed the penetration enhancement of higher concentrations during pressure treatment and of lower concentrations during subsequent storage.
Canadian green export lumber is protected against sapstain and mould by surface treatment with sapstain control products. For this purpose, coastal sawmills in British Columbia use sapstain control formulations based on didecyldimethylammonium chloride (DDAC). All Canadian green export lumber destined for Europe is also heat treated (pasteurized), in line with requirements to reduce the risk of transferring pathological nematodes to European forests. Recent experience has shown that the anti-stain performance of DDAC-treated wood is sometimes reduced after the wood has been heat treated. In the absence of research into this problem, the reasons for this remain speculative. It is possible that heat treatment modifies the interaction between the problem fungi and the wood (for example, heat treatment may clear a niche for problem fungi to become established or mobilize nutrients which stimulate fungal growth). It is also possible that heat treatment modifies the sapstain control treatment itself (Byrne, 1996). Although the chemical stability of DDAC is not affected by temperatures normally encountered during heat treatment, other factors may play a role (for example, kiln condensation may leach DDAC from the wood surface or the high humidity may affect the distribution of DDAC in the wood in such a way that the concentration of DDAC near the surface is no longer sufficient to inhibit fungal growth). The study described in this report was designed to examine the effects of heat treatment on DDAC retention and depth penetration under controlled conditions and to provide a basis for a qualitative comparison of DDAC penetration in spray-treated and dip-treated wood (Weigel and Daniels, 1995).
The recently revived interest in borate treatment for the production of termite-resistant lumber has led to the need for more rapid treatment processes. Pre-steaming prior to pressure treatment was known to have a number of potential benefits in terms of improved permeability, moisture distribution and vacuum. This process was therefore tried on western hemlock and amabilis fir Dodai (baby squares) in an attempt to achieve through-treatment without a diffusion period after pressure treatment. Western hemlock pre-steamed to a core temperature of 65 degrees C received a 25% increase in solution uptake and a 41% increase in mean heartwood penetration using a two hour pressure period. Amabilis fir pre-steamed to a core temperature of 90 degrees C received a 40% increase in solution uptake but no measurable increase in heartwood penetration. This was because penetration measured from the heartwood face was virtually complete in the amabilis fir treated without pre-steaming. Pre-steaming hemlock and amabilis fir Dodai appears to be a very effective means of improving uptake during pressure treatment. Further optimisation of this process is still possible.
The recent interest in borate treatment for the production of termite-resistant lumber has led to the need for improved treatment processes. Pre-steaming prior to pressure treatment was known to have a number of potential benefits in terms of improved permeability, moisture distribution and effectiveness of the vacuum. This process was therefore tried on western hemlock dodai (105 mm squares) in an attempt to achieve 80% cross sectional penetration with a minimal diffusion period after pressure treatment. Western hemlock pre-steamed to a core temperature of 82 degrees C in four hours took up almost double the amount of treating solution of end-matched unsteamed samples. There was an improvement in mean heartwood penetration of 45% immediately after treatment and a 134% increase in penetration after one week storage. This was not entirely due to diffusion within the wood but to mass flow of treating solution continuing after the end of the pressure process. After one week storage 64% of samples had 80% of the cross section penetrated. Reducing the vacuum time from 30 minutes to zero had a detrimental effect on penetration. Increasing time under vacuum to 60 minutes provided no beneficial effect. Pre-steaming of hemlock dodai appears to be a very effective means of improving uptake during pressure treatment.
Wood preservation standards typically specify quality assurance procedures to determine whether wood is adequately treated. As a result there is a need to identify sapwood and heartwood, and measure preservative retention and penetration. For spruce and hem-fir there are no reliable methods to differentiate sapwood and heartwood. For carbon-based preservatives, preservative retention measurement typically requires GC or HPLC analyses; the only methods available to determine penetration involve detecting a surrogate in the formulation rather than the active ingredients. Multivariate models based on near infrared (NIR) spectra have been used to predict a wide range of wood properties over the past 20 years. The present research evaluates the potential use of NIR-based models as quality assurance tools for the wood preservation industry. Models were developed to differentiate hemlock and amabilis fir sapwood and heartwood. Attempts to differentiate spruce sapwood and heartwood were unsuccessful. NIR-based models were also able to differentiate untreated wood from wood treated with DDACarbonate and wood treated with tebuconazole. Models developed to predict DDACarbonate and tebuconazole retention were moderately accurate, but likely not precise enough to replace current quantitative assays. However, the sensitivity to the presence of the actives may be sufficient for estimating preservative penetration. Further work is needed using small probes suitable for scanning increment cores to adapt this technology for industrial use.
In addition to conventional NIR, hyperspectral images were obtained to differentiate untreated wood from DDACarbonate- and tebuconazole-treated wood, but accurate calibrations could not be developed.