What is the standard size of a test specimen for natural durability testing?

300 mm long with a cross-section of 38 x 38 mm (Clause 3.1.1).

How often should the submerged test specimens be inspected?

At intervals not exceeding six months (Clause 7.1).

How is the extent of damage by borers evaluated?

Specimens are visually examined and given a destruction rating from 0 (sound) to 100 (completely destroyed) as defined in Table 1.

How are different timbers classified based on the test?

Timbers are classified into four classes (Class I to Class IV) based on their average life in the test, as specified in Table 2.

IS 6791

: 1973

Method of testing natural durability of timber and efficacy of the wood preservatives against marine borers

CurrentSpecializedTesting MethodMaterials Science · Timber and Timber Stores

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This standard specifies the method for conducting field tests in sea harbours to determine the natural durability of timber and the efficacy of wood preservatives against attack by marine borers. It details the size of test specimens, the apparatus for immersion, and the procedure for inspection and evaluation of borer damage over time.

Method of testing natural durability of timber and efficacy of the wood preservatives against marine borers

Quick Reference Values

Natural durability test specimen size300 x 38 x 38 mm

Preservative efficacy test specimen size150 x 38 x 38 mm

Minimum specimens per timber species/preservative5

Maximum inspection interval6 months

Destruction rating scale0 (Sound) to 100 (Completely destroyed)

Practical Notes

This is a long-term exposure test; meaningful results often take several years. The test location must have known, significant marine borer activity.

The standard has been reaffirmed multiple times (e.g., 2003, 2018), indicating its continued validity without major technical revisions.

Proper identification of both the timber specimens and the marine borers causing the damage is crucial for accurate reporting.