This guide is intended to discuss mold-related issues and to assist the industry in the delivery of clean, mold-free products to the marketplace. Mold continues to be undesirable on wood products and can cause rejection of shipments by the customers and economic losses to the industry. This report provides an historic perspective on mold, defines mold and discusses why it became a major issue in the marketplace and how this relates to wood products. The main factors required for mold growth and expansion are discussed, as are methods of limiting mold growth. The best method of mold control is moisture control, which includes initial drying and keeping wood products dry.
Specifically we give best practice guidelines for controlling mold on logs, lumber, plywood/veneers, other composite panel products, wood chips/residues, and for wood products in service (buildings). Lumber is one of the key products of the wood industry and several specific guidelines in regard to mold control for lumber are available and covered in depth. This includes air-drying, kiln-drying, phytosanitary heat treatment, and chemical prophylactic treatment of green lumber. Some circumstances where control of moisture is not feasible will require either chemical treatments or water barriers to prevent mold growth. There is also a special section on lumber packaging and wrapping, and water repellents. Finally, the report reviews existing guidelines for mold cleaning and remediation.
Development of bluestain in logs prevents the Canadian forest industry from producing maximum-value products from a considerable portion of the resource every year. The major purpose of this project was to determine the practical and economic feasibility of using an albino stain of a common bluestain fungus Ophiostoma piliferum (Cartapip 97, recently renamed Sylvanex) or equivalent albino fungi to control sapstain in lodgepole pine logs. We also tested the Forintek's eastern laboratory integrated control technology (fungus Gliocladium roseum with alkali). Different activities were planned but as results developed some had to be modified or dropped and others added to the planned work. The various aspects of this work are described in the set of reports that are included in the appendices.
Stains - Fungal - Control - Tests
Pinus contorta Dougl. var. latifolia - Stains - Fungal
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
New Zealand will soon be in a position to export a large wood surplus, which will compete with Canadian exports. Radiata pine has a natural advantage of being readily treatable. 20% of New Zealand's total lumber production is treated with boron salts, either hot borate or cold thickened borate, followed by a diffusion period of 6-8 weeks for 50 mm thick wood. The lumber is usually sold green. There is an active research program to improve boron treatment. The viability of transferring New Zealand treatment practices to B.C. sawmills will depend on economics, technical and marketing considerations. There are potential world markets for borate treated wood which could be partly filled by western Canadian softwoods such as hem-fir and alpine fir. COFI and Forintek should investigate further and develop these markets. Impediments should be identified and addressed. Forintek should ensure it is up-to-date in knowledge of boron treatments used in New Zealand and elsewhere, and ensure that it has the technical information required to treat western Canadian softwoods
The objective of the program is to catalyze the development of boron as an environmentally acceptable chemical treatment and improve process technology to produce a boron-treated lumber product. There is a need for low environmental impact wood preservatives, particularly for the residential market. Although the hazards associated with treated wood may be negligible, the public perception of potential hazards may be sufficient to proscribe the future use of the present preservatives. Boron is an environmentally benign preservative which has been used for many years in New Zealand and Australia and has started to be used in the U.S.A. but is not yet used in Canada. There is a potential market for termite-proof wood for southern Ontario and boron promises to be a suitable candidate. Opportunities also exist in overseas markets for boron treated lumber provided that a rapid and cost effective diffusion process can be developed. Western softwoods, which are naturally wet species, particularly lend themselves to diffusion treatments with boron. Despite there being a good body of scientific literature available on borate treatment of wood there is a lack of basic technical knowledge on borate treatment of Canadian woods. This project seeks to address this need.
Discolourations of hem-fir, usually called hemlock brownstain, have become an economically important problem with the move towards increased kiln-drying of the wood species mixture and added-value products in which discolourations cannot be tolerated. These discolourations, clearly different from sapstain, can occur in several types and intensities and are a serious problem in high-value markets. Because little is known about their causes means for their control are still unavailable. Therefore fundamental research was initiated to elucidate the biology and chemistry of hemlock brownstain and to suggest control measures. A post graduate student was hired to undertake laboratory and field work as part of a Ph.D. program. The thesis subject was "the role of microorganisms in the phenomenon of hemlock brownstain". The thesis covers: a literature review; laboratory work to locate the stain and define its nature; a storage study of logs and lumber to monitor progress in development of brownstain; fungal isolation work and sap characterization studies; in vitro production of hemlock brownstain in wood and sap; and additional laboratory experiments to determine what factors influence the formation of the brownstain. In addition to the thesis research the role of bacteria in the formation of the stain was investigated in the laboratory and the ability of various chemicals, including fumigants, to prevent the stain was tested in small-scale field test. This report provides an overview of the findings and provides recommendations for future work. The experiments clearly demonstrated that a non-specific microflora can produce brownstain which led to the hypothesis that microorganisms could be involved in hemlock brownstain. Based on our knowledge of the coastal sawmilling industry a strategy of minimizing fungal infection and rapid handling of the tree breakdown into final wood products could probably be the best approach to help reduce the problem. In terms of future work we recommend that work to understand the mechanism of DDAC in mitigation of the browning take precedence in future work on hemlock brownstain.
The natural wood appearance of many species can be affected by a variety of undesirable "non-microbial" discolourations, which reduce the value of wood products. In contrast to sapstain, caused by fungi, prevention of these discolourations has rarely been demonstrated in practice. Discolourations of hem-fir have become an economically important problem with the move towards increased kiln-drying of the wood species mixture and added-value products in which discolourations are less tolerable. A literature review was done to survey both general information on "non-microbial" discolourations and more specifically information on discolourations of western hemlock and amabilis fir. Although discolouration of hem-fir lumber has been a puzzle for many years, knowledge of its cause(s) is rudimentary. Most research into hem-fir discolourations has been conducted on only a few wood samples. Although polymerization of wood extractives has been proposed as the probable cause, involvement by bacteria and fungi are also suggested in the literature. Other factors involved in discolourations of other wood species, such as factors inherent in the living tree, season of tree felling, post mortem changes and log age and storage, are reviewed. The nature of specific wood extractive chemicals and the significance of other contributory factors need to be understood before preventive treatments can be devised to maintain the natural colour in hem-fir products. Research recommendations include microscopic and histochemical techniques.
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