How does IS 401 classify timber durability?

Based on graveyard tests: Class I (>120 months life), Class II (60-120 months), and Class III (<60 months).

What is the recommended moisture content before treatment?

Timber should typically be seasoned to a moisture content of 15% to 25% prior to pressure treatments.

What are the common types of wood preservatives covered?

Oil type (e.g., Coal tar creosote), Organic solvent type, and Water-soluble type (e.g., Copper-Chrome-Arsenic or CCA).

IS 401

: 2001

Code of Practice for Preservation of Timber

CurrentSpecializedCode of PracticeMaterials Science · Timber and Wood

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This code covers the recommended practices for the preservation of timber. It classifies timber based on natural durability and treatability, providing guidelines for selecting appropriate preservative types, treatment methods, and retention levels to protect wood from decay, fungi, marine borers, and insect attacks.

Specifies methods and good practices for the preservative treatment of timber to protect it against decay, insects, and marine borers.

Quick Reference Values

Class I Timber DurabilityAverage life > 120 months

Class II Timber DurabilityAverage life 60 to 120 months

Class III Timber DurabilityAverage life < 60 months

Ideal moisture content before pressure treatment15% to 25%

Practical Notes

Timber must be properly seasoned (barked and dried) prior to preservative treatment to allow adequate penetration, except for specific diffusion processes.

Heartwood is generally highly resistant to preservative penetration; therefore, treatments primarily aim to thoroughly protect the outer sapwood.

Refractory timbers (species that are hard to treat) may require incising (making shallow cuts) before pressure treatment to ensure sufficient preservative absorption.