What is meant by the 'threshold value' of a preservative?

It is the minimum concentration or retention level of the preservative in the wood that effectively prevents significant decay by the test fungus.

How is decay measured in this test?

Decay is assessed quantitatively by calculating the percentage weight loss of the treated test blocks after exposure to the fungi.

What type of fungi are used for these tests?

Specific virulent strains of brown rot and white rot fungi, which are known to cause severe structural degradation in timber, are used.

How long does the testing process take?

The incubation phase alone typically requires 12 to 16 weeks to allow sufficient time for fungal growth and potential decay.

IS 4873

: 2000

Methods of laboratory testing of wood preservatives against fungi and borers (powder post beetles) : Part 2 Determination of threshold values of wood preservatives against borers (powder post beetles)

CurrentSpecializedTesting MethodMaterials Science · Timber and Timber Stores

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This standard outlines the laboratory testing methods for determining the threshold values of wood preservatives against wood-destroying fungi. It establishes the minimum preservative retention required to effectively prevent fungal decay by measuring the weight loss of treated timber blocks after controlled incubation.

Quick Reference Values

Standard test block dimensions19 x 19 x 19 mm

Incubation temperature25 ± 1°C

Incubation relative humidity70 ± 5%

Typical incubation duration12 to 16 weeks

Drying oven temperature for block weight103 ± 2°C

Key Formulas

Weight loss (%) = [(W1 - W2) / W1] x 100 — where W1 is initial oven-dry weight and W2 is final oven-dry weight after incubation

Practical Notes

Maintain strict sterile conditions during the preparation and infection of test blocks to prevent contamination by unintended mold or fungi.

Oven-dry weights must be carefully recorded before and after testing, as the assessment relies entirely on accurate mass loss calculation.

Ensure test blocks are free from natural defects like knots or cracks which could skew preservative absorption or weight loss.