Preservation of Timber - Code of Practice

IS 401 - Scope Summary with Key Formulas and Tables

1. Scope Overview:

• Covers preservation of timber by various chemical treatments.
• Includes weighing methods for timber and preservatives.
• Specifies moisture content determination and penetration testing.
• Refers to related IS standards for preservatives and treatment methods.

2. Key Formula: Moisture Content (Clause 3.1)

[ \text{Moisture Content (%)} = \frac{B - C}{C - A} \times 100 ]

• A: Mass of empty weighing bottle (with stopper)
• B: Mass of bottle + sample before drying
• C: Mass of bottle + sample after oven drying

3. Scales & Balances (Clause 10.4)

• Track scales for timber charge before/after treatment.
• Tank scales for preservative absorption measurement.
• Tolerance allowed: ± 2% on scales.

4. Recommended Preservation Practices (Table 2 - Clause 8.2)

Referenced Indian Standards in IS 401:2001 (Clause 2, Annex A)

IS 401 refers to several key Indian Standards related to wood preservatives, seasoning, and testing methods:

Key Notes:

• Track and tank scales must have ±2% tolerance for weighing timber and preservatives (Clause 10.4).
• These standards cover chemical specifications, treatment methods, and testing procedures essential for timber preservation.

This list helps ensure quality control and standardization in timber treatment and preservation per IS 401.

IS 401 - Terminology & Key Specifications Summary

Key Terminology (from Clause 10.4 & related clauses):

• Track Scales: Weigh timber before & after treatment to calculate preservative absorption.
• Tank Scales: Measure preservative depth change in treatment tanks.
• Balances: Used for moisture content and chemical weighing; ±2% tolerance allowed.
• Assay Zone: Portion of timber where preservative retention and penetration are measured.
• Recommended Absorption: Amount of preservative (kg/m³) retained in timber after treatment.

Important Specifications & Tables:

Preservative Loading Example (CCA):

Penetration Requirements:

• Group 1: ≥30 mm sapwood fully penetrated; sleepers ≥40 mm.
• Groups 2-7: Sapwood fully treated; penetration varies 3-12 mm by treatability class.

Notes:

• Chromium acts as fixative, copper/arsenic/boron provide protection.
• Absorption values refer to dry chemical content.
• Use boric acid treatments for timber in contact with food or pencil sl

IS 401: Types of Preservatives - Key Points

1. Types of Preservatives (Clause 3 & 4)

• Water-Soluble (Fixed) Type (Clauses 3.3.2, 4.4)

  • Compositions include:
    • Copper-chrome-arsenic (CCA)
    • Acid-cupric-chromate
    • Copper-chrome-boron
    • Zinc meta-arsenite
    • Borated copper-chrome-arsenic
    • Ammoniacal copper-arsenate
  • Mechanism: Chromium fixes toxic elements (As, Cu, B) in timber, reducing leaching.
  • Application: Applied cold; drying for 2-3 weeks needed for fixation.
  • Properties: Broad-spectrum efficacy, water-resistant after fixation.

• Organic Solvent Type (Clause 4.2)

  • Preservatives dissolved in organic solvents.
  • Permanent and clean to handle if light solvents used.
  • Solvent chosen based on preservative solubility and end-use.

2. Fixation Process Summary (Water-Soluble Type)

flowchart LR
    A[Preservative Mixture] --> B[Applied Cold on Timber]
    B --> C[Fixative Salt (Dichromate)]
    C --> D[Drying for 2-3 Weeks]
    D --> E[Fixed Toxic Elements in Timber]
    E --> F[Water-Resistant & Durable Timber]

Note: Refer Annex A of IS 401 for detailed standards and latest revisions.

IS 401: Damage and Deterioration of Timber – Key Points

1. Durability Classification (Clause 8.3, Annex B)

• Timber durability is tested by exposing heartwood to fungi and termites.
• Durability varies with species and local conditions.
• Table 3 (not fully shown here) classifies species by durability and treatability grade.

2. Treatability & Preservation (Clause 1.5, Table 2)

• Preservatives: Common types include CCA, CCB, BCCA, Zinc naphthenate, Copper abietate, TCP.
• Recommended absorption: Varies by timber group and preservative, e.g.,
  • Group 1 (poles, piles): minimum 30-40 mm penetration
  • Groups 2-7: 3-12 mm penetration depending on treatability class.
• Chemical loading example for CCA:
  • 8 kg/m³ total dry salt loading = 4 kg Cu + 3 kg Cr + 1 kg As per m³.

3. Treatment Methods

• Brushing, spraying, dipping, pressure treatment.
• Incision recommended for refractory heartwood (12-19 mm deep).
• Prophylactic treatment for storage: Sodium pentachlorophenate + borax.

4. Important Notes

• Chromium acts as a fixative, not protective.
• Boric acid/borax treatment only for food-contact timber.
• Avoid arsenic preservatives in packing cases used as fuel.

Summary Table: Minimum Penetration Depths for Preservative Treatment

flowchart TD
    A[Timber Species] --> B{Durability Class}
    B -->|High| C[Group 1: Long life, ground contact]
    B -->|Medium| D[Groups 2-4: Moderate durability]
    B -->|Low| E[

IS 401: General Requirements for Preservation of Timber

Key Points & Formulas

• Moisture Content (%) (Clause 3.1):

  [ \text{Moisture content} = \frac{B - C}{C - A} \times 100 ]

  where,

  • (A) = mass of weighing bottle (with stopper)
  • (B) = mass of bottle + sample before drying
  • (C) = mass of bottle + sample after oven drying

• Types of Preservatives:

  • Copper-Chrome-Arsenic (CCA)
  • Copper-Chrome-Boron-Arsenic (CCB/BCCA)
  • Creosote & Coal Tar Creosote (CTC/LTC)
  • Others like ACA, Copper/Zinc naphthenates, TCP

• Preservative Penetration (Annex D):
  Methods for CCA, CCB, and copper-chrome-arsenic compositions are specified for ensuring adequate penetration.

Recommended Preservation Practices (Table 2 Summary)

IS 401: Methods of Treatment – Key Points & Tables

1. Material Preparation (Clause 6.1)

• Material must be sound.
• Except for diffusion, Boucherie, or APM methods, timber must be dried to specified moisture content before treatment.
• All wood working (cutting, boring) must be done prior to treatment.
• Table 1 (not fully provided) gives permissible moisture content before treatment.

2. Preservative Treatment (Clause 8.2 & Table 2)

• Note: Chromium acts as fixative, does not protect wood.
• For non-durable heartwood, incision to 12–19 mm depth recommended to improve penetration.

3. Preservative Loading Formula

[ \text{Preservative Retention (kg/m}^3) = \frac{\text{Weight of preservative absorbed (kg)}}{\text{Volume of timber (m}^3)} ]

• Example for CCA: 8 kg/m³ total salts = 4 Cu + 3 Cr + 1 As (kg/m³).

4. Moisture Content Measurement & Weighing (Clause 10.4)

• Use track scales for timber weight before/after treatment.
• Use tank scales to measure preservative volume change.
• Moisture content by small balances.
• Tolerance: ±2% for all scales.

IS 401 - Recommended Practices for Different Service Conditions (Clause 8.2, Table 2)

Key Notes on Treatment & Absorption

• Preservative loading example for CCA (8 kg/m³):
  • Copper: 4 kg/m³
  • Chromium: 3 kg/m³ (fixative)
  • Arsenic: 1 kg/m³
• Penetration requirements:
  • Group 1 (ground contact):

IS 401: Inspection & Testing of Treated Timber - Key Points

1. Preservative Retention & Absorption

• Absorption is measured in kg/m³ of dry chemical retained in timber.
• Example for CCA (Chromated Copper Arsenate) with 8 kg/m³ dry salt loading:
  • Copper = 4 kg/m³
  • Chromium = 3 kg/m³ (fixative, no protection)
  • Arsenic = 1 kg/m³

2. Assay Zones & Penetration Requirements

3. Recommended Absorption for Various Service Conditions (Table 2 Highlights)

IS 401: Equipment and Instrumentation Key Points

1. Thermometers (Clause 10.2)

• Check against standard thermometers certified by National Physical Laboratory.
• Permissible variation: ±1°C.

2. Scales and Balances (Clause 10.4)

• Track scales: Weigh timber before and after treatment.
• Tank scales: Measure preservative depth before and after treatment.
• Balances:
  • Small: Moisture content of timber specimens.
  • Large: Weigh preservatives and chemicals.
• Permissible tolerance: ±2%.

3. Pressure and Vacuum Gauges (Clause 10.3)

• Compare with standard gauges certified by National Physical Laboratory.
• Any error beyond permissible limits must be recorded until corrected.

Summary Table: Equipment Accuracy

Additional Notes:

• Use recording instruments wherever possible for accuracy.
• Maintain records of errors exceeding limits until equipment is restored.

flowchart LR
    A[Equipment] --> B[Thermometers]
    A --> C[Scales & Balances]
    A --> D[Pressure & Vacuum Gauges]

    B --> E{Check against}
    E --> F[Standard Thermometers]
    F --> G[±1°C tolerance]

    C --> H{Types}
    H --> I[Track Scales]
    H --> J[Tank Scales]
    H --> K[Balances]
    K --> L[Small - moisture content]
    K --> M[Large - preservatives]
    C --> N[±2% tolerance]

    D --> O[Compare with standard gauges]
    O --> P[Record errors beyond limits]

For detailed preservative specifications, refer to the IS standards listed in Annex A (e.g., IS 218, IS 882, IS 1078).

IS 401: List of Referred Indian Standards

This standard references key IS codes related to timber preservation and treatment. Below is a concise table of important referred standards:

Key Notes:

• These standards cover preservatives, seasoning, chemical specifications, and treatment methods.
• IS 2753 (Part 1) details methods for estimating preservatives like copper, arsenic, chromium, zinc, boron, creosote, and fuel oil.
• Tolerances for scales and balances used in timber treatment (Clause 10.4) are ±2%.

Summary Diagram of Reference Relationships

graph LR
A[IS 401] --> B[Preservatives Specs]
A --> C[Seasoning & Treatment]
A --> D[Testing & Estimation Methods]
B --> IS218[IS 218: Creosote]
B --> IS882[IS 882: Lindane]
B --> IS1078[IS 1078: Copper Naphthenate]
C --> IS

IS 401 - Durability & Treatability of Timber Species

Key Points from Clause 8.3 & Annex B:

• Durability: Based on fungal decay and termite attack tests on heartwood (6 specimens/species).
• Treatability: Grade indicating ease of preservative treatment.
• Classification: Comparative durability in exposed and ground-contact conditions.
• Source: Data from Forest Research Institute, Dehra Dun.

Table 3: Durability & Treatability Summary (Excerpt)

Note: Durability classes typically are

• Very Durable
• Durable
• Moderately Durable
• Non-Durable

Treatability grades are

• Easy
• Moderate
• Difficult

Practical Use:

• Select Very Durable species for ground contact without treatment.
• Use preservative treatment for Moderately Durable and Non-Durable species.
• Treatability guides preservative penetration methods and duration.

flowchart LR
    A[Timber Species] --> B[Durability Test]
    B --> C{Classify Durability}
    C -->|Very Durable| D[Use Untreated]
    C -->|Durable/Moderate| E[Preservative Treatment]
    C -->|Non-Durable| E
    E --> F{Treatability Grade}
    F -->|Easy| G[Simple Treatment]
    F -->|Moderate| H[Standard Treatment]
    F -->|Difficult| I[Special Treatment]

For detailed species-wise data, refer to Table 3 in Annex B of IS 401.

IS 401: Moisture Content Determination – Key Points

Procedure (Clause 2.1)

• Sample is taken immediately after boring/cutting.
• Place sample in a tared weighing bottle (with stopper).
• Weigh bottle + sample before drying → B.
• Dry sample in oven at 103 ± 2℃ for 24 hours (stopper removed).
• Cool in desiccator, stopper, then weigh → C.
• Weigh empty bottle + stopper → A.

Moisture Content Formula (Clause 3.1)

[ \text{Moisture Content (%)} = \frac{B - C}{C - A} \times 100 ]

Where:

• A = mass of empty bottle + stopper
• B = mass of bottle + stopper + wet sample
• C = mass of bottle + stopper + dry sample

Sampling (Clause 1.3)

• For green or evenly dried timber of same species, take about 12 samples to get average moisture content.

Summary Table

flowchart TD
    A[Sample Bored/Cut] --> B[Place in Tared Bottle]
    B --> C[Weigh Bottle + Wet Sample (B)]
    C --> D[Dry in Oven 103±2℃ for 24 hrs]
    D --> E[Cool in Desiccator, Stopper]
    E --> F[Weigh Bottle + Dry Sample (C)]
    F --> G[Calculate Moisture Content]

This method ensures accurate moisture content essential for timber treatment and quality control as per IS 401.

IS 401: Methods for Determining Penetration and Absorption of Preservatives

1. Moisture Content Calculation (Clause 3.1)

[ \text{Moisture content (%)} = \frac{B - C}{C - A} \times 100 ]

• A = Mass of weighing bottle + stopper (empty)
• B = Mass of bottle + sample before drying
• C = Mass of bottle + sample after oven drying

2. Penetration Determination (Annex D, Clause 9.5)

• Copper-Chrome-Arsenic & Acid-Cupric-Chromate Compositions:
  • Use treated wood cross-sections or borings.
  • Apply reagents to observe red copper trichlorophenate formation.
  • Note: Dark treatments may obscure color.
  • Application methods: brush, flow-on, or spray (Clause 4.9).

3. Absorption Determination (Clause 9.4)

• Perform chemical analysis of treated timber.
• Compare with:
  • Service tank readings.
  • Weight difference before and after treatment (per IS 2753 Part 1).

4. Preservative Selection & Treatment (Clause 8.2, Table 2)

• Table 2 provides recommended preservative types, treatment processes, absorption, and penetration values for various timber uses.

Summary Diagram of Process

flowchart TD
    A[Select Timber Sample] --> B[Measure Moisture Content]
    B --> C[Treat with Preservative]
    C --> D[Take Cross-Sections/Borings]
    D --> E[Apply Chemical Reagents]
    E --> F[Observe Penetration (Color Reaction)]
    C --> G[Chemical Analysis for Absorption]
    F & G --> H[Compare with Tank Data & Standards]

This concise framework ensures reliable evaluation of preservative penetration and absorption as per IS 401.

IS 401: Recommended Treatment for Timber Not Removable from Structures

Key Points & Specifications:

• Preservatives for timber not removable:

  • Zinc naphthenate (1.5% solution)
  • Copper abietate (1% solution)
  • TCP (1% solution)

• Application methods: Brushing, spraying, or dipping.

• Recommended absorptions (kg/m³) for various preservatives:

• Penetration requirements:

  • For ground-embedded timber (Group 1): Minimum 30 mm sapwood penetration.
  • For sleepers: Minimum 40 mm penetration.
  • For other groups: Sapwood fully treated; penetration varies 3-12 mm depending on group.

• Process of treatment:

  • Hot and cold process (if applicable), diffusion treatment, or pressure processes preferred.
  • For timber in contact with ground or soil, pressure treatment is recommended.

• Moisture content before treatment: Refer Table 1 of IS 401 (typically dried to appropriate moisture content except diffusion/APM methods).

Summary Table (Selected Groups):