This standard specifies a laboratory procedure to assess the effectiveness of wood preservatives in protecting coniferous wood from soft rot decay caused by the fungus Chaetomium globosum. It is vital for researchers, manufacturers, and quality assurance personnel to determine the minimum preservative concentration required to prevent soft rot under controlled laboratory conditions.
Overview
This standard specifies a laboratory procedure to assess the effectiveness of wood preservatives in protecting coniferous wood from soft rot decay caused by the fungus Chaetomium globosum. It is vital for researchers, manufacturers, and quality assurance personnel to determine the minimum preservative concentration required to prevent soft rot under controlled laboratory conditions.
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Contents
Structure
This section defines the scope of the standard relating to wood and wood-based product testing methods, quality control, and properties. It harmonizes with global standards while incorporating Indian forestry data from the Forest Research Institute, Dehra Dun. The section emphasizes uniform reporting practices following IS: 2-1960+ rounding rules, aiming to establish consistent guidelines for timber testing and evaluation in construction and engineering contexts.
This part describes the fundamental concept behind the test, which evaluates the toxicity and efficacy of wood preservatives on treated samples, including effects after leaching. It highlights the conditioning process to simulate environmental exposure, followed by bioassay or chemical analysis to determine residual preservative activity. Results are to be rounded according to IS 2-1960+ for standardization.
Guidelines for preparing test blocks are outlined here. Blocks are cut from knot-free mango wood to dimensions of 5.0 cm length, 2.5 cm width, and 0.5 cm thickness, with the grain aligned longitudinally. Samples are oven-dried at 100–105°C to constant weight. Twelve blocks per preservative concentration are used, selecting concentration ranges to bracket the expected threshold retention. Culture medium composition is also detailed for fungal growth.
This section specifies the medium used for fungal culture growth, listing precise quantities of ammonium nitrate, potassium dihydrogen phosphate, magnesium sulphate, ferrous sulphate, agar, and distilled water per liter. Preparation instructions include dissolution, sterilization at 120°C under pressure, and aseptic handling with cotton wool plugs. Procedures for placing sterile filter paper and applying spore suspensions are also provided.
Detailed steps for conducting the preservative efficacy test are given, including sample preparation, leaching conditioning to simulate environmental exposure, incubation periods, toxicity evaluation, and result calculation. Emphasis is placed on adhering to incubation durations and following IS: 2-1960+ rounding methods for consistent reporting.
Describes procedures for examining wood blocks after fungal exposure. Blocks are incubated at 30 ± 0.5°C for six weeks with moisture maintained via sterile water on cotton wool. Weight loss is measured by comparing pre- and post-exposure oven-dry weights to assess decay extent, providing a quantitative basis for preservative effectiveness.
Explains the formula to calculate preservative retention in treated wood blocks, based on solution uptake weight, preservative concentration, and block volume. Results are expressed in g/cm³ or converted to kg/m³. Reporting follows IS: 2-1960+ rounding rules to ensure clarity and comparability.
Outlines the method of reporting test outcomes including rounding conventions. It details the calculation of percentage weight loss due to decay and provides criteria for interpreting results, where weight loss below 3% is considered experimental error and insignificant, while higher values indicate notable decay and preservative failure.
Frequently Asked
The standard specifies using mango wood blocks measuring 5.0 cm in length, 2.5 cm in width, and 0.5 cm in thickness, with the grain oriented along the length. Blocks must be free from knots, mold, and stains, and oven-dried at 100–105°C to constant weight before treatment. Twelve blocks per preservative concentration are prepared, with subsequent conditioning such as leaching or drying depending on preservative type, ensuring uniformity for testing against soft rot fungi.
Preservative application involves placing oven-dried mango wood blocks into a beaker, applying a vacuum of 60 mm Hg for 30 minutes to remove air, then introducing preservative solution from a separating funnel. After vacuum release, blocks soak in the solution for 30 minutes, are wiped dry, and weighed. Testing usually involves twelve blocks per concentration, with weight/weight-based concentrations selected to bracket the expected minimum effective retention. Water-borne treated blocks undergo leaching at 40 ± 5°C for 100 hours with periodic water changes, while solvent-based treated blocks are air-dried for four weeks.
The fungus Chaetomium globosum Kunze is used as the test organism to simulate soft rot decay. Cultures are prepared on malt agar 2–3 weeks prior to testing. This species is chosen due to its known ability to cause soft rot in wood, making it a reliable agent for assessing preservative efficacy under laboratory conditions.
Weight loss is calculated by measuring the oven-dry weight of wood blocks before exposure (W2) and after exposure to fungal decay (W3). The percentage weight loss is computed as ((W2 − W3) / W2) × 100. Adjustments are made for preservative absorption and evaporation using control samples. A weight loss below 3% is considered within experimental error and indicates effective preservation, whereas higher losses signify significant decay and reduced preservative efficacy.
Test blocks are incubated at a controlled temperature of 30 ± 0.5°C for six weeks inside flasks containing cotton wool moistened aseptically with sterile water to maintain humidity. Fungal spores of Chaetomium globosum, prepared 2–3 weeks earlier and suspended in distilled water, are sprayed onto sterile filter paper placed on the culture medium. This environment ensures consistent fungal growth and attack on the test specimens.
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