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

IS 6791: Scope & Key Specifications

• Scope:
  IS 6791 focuses on the method of exposure for testing wood specimens treated with preservatives, emphasizing international coordination and Indian field practices.

• Exposure Method (Clause 2.4):

  • Specimens treated with two preservatives are suspended vertically on opposite sides of a rectangular raft.
  • Untreated control specimens are placed on the other two sides.
  • Specimens tied at 5 cm intervals, starting 0.35 m below low water mark.
  • Large tests can use the raft’s central hall for additional specimens.

• Raft Design (Fig. 1):

  • Block size: 30 x 5 x 5 cm
  • Raft has 15 racks (7 central hall, 8 around raft), each 180 cm long.
  • Holds 5 strings per rack, with 4+ blocks per string.
  • Total capacity: 300 blocks per raft.

• Rounding Off:
  Numerical values rounded as per IS 2-1960.

flowchart LR
    A[Wood Specimens Treated] -->|Suspended Vertically| B[Rectangular Raft]
    B --> C[Two sides: Treated with Preservatives]
    B --> D[Other two sides: Untreated Controls]
    B --> E[Blocks tied at 5 cm intervals]
    B --> F[Starting 0.35 m below low water]
    B --> G[Capacity: 300 blocks per raft]

This setup ensures standardized, reproducible exposure testing of wood preservatives.

Selection of Timber for Specimens - IS 6791 Key Points

• Specimen Source (Clause 2.2):

  • Use heartwood from commercial timber species suitable for sea water.
  • Select specimens from at least two trees per species.
  • If species grow in multiple areas with property variations, obtain specimens from each growing area.

• Number of Specimens (Clause 2.3):

  • For each tree/species:
    • Use 1 untreated specimen.
    • Use 4 treated specimens (2 preservatives × 2 absorption levels).
    • Preservatives:
      • Oil type: Creosote or creosote-fuel oil (1:1)
      • Water soluble type: Copper-Chrome-Arsenic (CCA)
    • Absorption levels:
      • Creosote: 160 kg/m³ and 320 kg/m³
      • CCA: 16 kg/m³ and 32 kg/m³
    • Prepare 3 sets for each absorption level.

• Statistical Design (Clause 2.8.1):

  • Use suitable statistical design for specimen installation.
  • Include 2 standard species (1 hardwood, 1 softwood) treated by standard preservatives as controls.
  • Perform standard statistical analysis on results.
  • Refer to IS 401-1967 for preservation and treatment processes.

Summary Table of Specimen Preparation

flowchart TD
    A[Select Species & Trees] --> B[Extract Heartwood Specimens]
    B --> C[Prepare Specimens]
    C --> D[Untreated Specimen (1)]
    C --> E[Treated Specimens (4)]
    E --> F[

IS 6791 Key Specifications for Size and Number of Specimens

1. Size of Specimens (Clause 2.1)

• Dimensions: 30 cm (length) × 5 cm (width) × 5 cm (thickness)

2. Number of Specimens (Clause 2.3)

• Preservative Types:

  • Oil type (e.g., Creosote or Creosote-fuel oil 1:1)
  • Water-soluble type (e.g., Copper-Chrome-Arsenic composition)

• Absorption Levels:

  • Creosote: 160 kg/m³ and 320 kg/m³
  • Copper-Chrome-Arsenic: 16 kg/m³ and 32 kg/m³ (dry salt)

• Specimen Count per Tree Species:

  • 4 treated specimens (2 preservatives × 2 absorption levels)
  • 1 untreated specimen (control)
  • Total: 5 specimens per tree species per set

• Sets:

  • 3 sets per absorption level → ensures statistical reliability

3. Exposure Setup (Clause 2.4)

• Specimens suspended vertically on a rectangular raft at 5 cm intervals starting 0.35 m below low water mark.
• Raft capacity: Up to 300 blocks (15 racks × 5 strings × 4+ blocks per string)

Summary Table

flowchart LR
    A[Select Tree Species] --> B[Prepare Specimens 30x5x5 cm]
    B --> C{Preservative Type}
    C --> C1[Oil Type (Creosote

IS 6791 - Method of Exposure for Timber Preservation Testing

Key Specifications (Clause 2.4)

• Specimen Arrangement:

  • Treated specimens with two different preservatives are suspended vertically on opposite sides of a rectangular raft.
  • Untreated control specimens are suspended on the other two sides.
  • Specimens tied with ropes at 5 cm intervals, starting 0.35 m below low water mark.

• Raft Dimensions and Capacity:

  • Raft length: 180 cm per side
  • Block size: 30 x 5 x 5 cm
  • Holds 15 racks (7 in central hall, 8 around raft)
  • Each rack holds 5 strings with 4+ blocks/string
  • Total capacity: up to 300 blocks per raft

Statistical Design (Clause 2.8.1)

• Use standard statistical methods for specimen installation and result analysis.
• Test at least two standard species (hardwood and softwood) treated with two standard preservatives each time to link results across tests.

Rounding Off (Clause 0.6)

• Follow IS 2-1960 for rounding numerical values in reporting.

Raft Layout (Simplified Diagram)

graph TB
    A[Treated Specimens (Preservative 1)]
    B[Treated Specimens (Preservative 2)]
    C[Untreated Controls]
    D[Untreated Controls]
    subgraph Raft
        A --- B
        C --- D
    end

References for Further Details

• IS 401-1967: Preservation of Timber
• IS 2-1960: Rules for Rounding Off
• IS 2753 (Part I & II): Estimation of Preservatives

This method ensures uniform exposure and reliable durability evaluation of treated timber specimens.

IS 6791 - Test Sites: Key Specifications & Setup

1. Specimen Size

• 30 cm x 5 cm x 5 cm blocks (Clause 2.1)

2. Number of Test Sites

• Depends on:
  • Variation in faunal composition
  • Intensity of biological attack
• Select as many test sites as possible for representative results (Clause 2.5)

3. Method of Exposure

• Specimens suspended vertically on a rectangular raft (Fig. 1)
• Arrangement:
  • Treated specimens with 2 preservatives on opposite sides
  • Untreated controls on other two sides
• Specimens tied at 5 cm intervals, starting 0.35 m below low water mark (Clause 2.4)

4. Raft Design

• 15 racks: 7 in central hall + 8 around raft
• Each rack: 180 cm long, holds 5 strings, 4+ blocks per string
• Total capacity: 300 blocks per raft

5. Statistical Design

• Use suitable statistical design per species tested
• Include at least two standard species (hardwood & softwood) treated with standard preservatives for benchmarking (Clause 2.8.1)

Summary Table:

flowchart LR
    A[Test Sites] --> B[Specimen Size: 30x5x5 cm]
    A --> C[Raft Setup]
    C --> D[Treated Specimens (2 preservatives)]
    C --> E[Untreated Controls]
    C --> F[Specimens tied at 5 cm intervals]
    C --> G[Submerged 0.35 m below low water mark]
    A --> H[Statistical Design]
    H

IS 6791 - Recording of Data: Key Points

• Counting Borer Holes:
  Count the number of borer holes for each major borer species on:

  • Four longitudinal surfaces
  • Two end surfaces (total 6 surfaces)

• Area Evaluation:
  Estimate the approximate area of borer holes on each surface separately.

• Percentage Calculation:
  Calculate the percentage of total borer hole area relative to the total surface area:
  [ \text{Percentage of borer holes} = \frac{\sum \text{Area of borer holes on all surfaces}}{\text{Total surface area}} \times 100 ]

• Rejection Criteria:
  Specimens may be rejected if ≥ 50% of the total surface area is covered by borer holes.

• Additional Data:
  If strength testing is available, record strength values to correlate borer damage with strength loss.

• Rounding Off:
  Final values should be rounded as per IS 2-1960.

Summary Table

flowchart TD
    A[Start: Inspect specimen] --> B[Count borer holes on 6 surfaces]
    B --> C[Estimate area of holes per surface]
    C --> D[Sum area of holes on all surfaces]
    D --> E[Calculate % area affected]
    E --> F{Is % area ≥ 50%?}
    F -- Yes --> G[Reject specimen]
    F -- No --> H[Specimen acceptable]
    H --> I{Strength test available?}
    I -- Yes --> J[Record strength data]
    I -- No --> K[End]

This method ensures consistent and standardized recording of borer damage per IS 6791.

Efficacy of Wood Preservatives (IS 6791)

Key Specifications & Test Setup:

• Species: Use at least two non-durable species (e.g., Mangifera indica (mango), Pinus roxburghii (chir)).
• Preservatives: Two standard types:
  • Oil-based (Creosote or Creosote-fuel oil 1:1)
  • Water-soluble (Copper-Chrome-Arsenic (CCA) composition)
• Absorption Levels:
  • Creosote: 160 kg/m³ and 320 kg/m³
  • CCA: 16 kg/m³ and 32 kg/m³ (dry salt basis)
• Specimens: For each species and preservative:
  • 4 treated specimens (2 absorption levels × 2 replicates)
  • 1 untreated specimen
  • 3 sets per absorption level (total 3 × 2 = 6 treated + untreated)
• Statistical Design: Use standard statistical analysis to compare treated vs untreated specimens and results across different test times.

Test Methods Referenced:

• IS 401-1967 (Preservation of Timber)
• IS 4873-1968 (Laboratory testing of preservatives against fungi)
• IS 6341-1971 (Soft rot testing)
• IS 6497-1972 (Natural durability evaluation)

Summary Table of Absorption Levels:

Statistical Evaluation Flow:

flowchart TD
    A[Select Species & Preservatives] --> B[Prepare Specimens at 2 Absorption Levels]
    B --> C[Conduct Laboratory & Field Tests]
    C --> D[Record Durability & Decay Data]
    D --> E[Perform Statistical Analysis]
    E --> F[Compare Treated vs Untreated & Across Tests]

Note: For detailed procedures on treatment, absorption measurement, and statistical methods, refer to IS 401-1967 and related IS codes listed.

IS 6791: Statistical Analysis of Results – Key Points

• Statistical Design (Clause 2.8.1):

  • Design tests based on the number of species selected.
  • Include at least two standard species (one hardwood, one softwood) treated with two standard preservatives each time tests are done.
  • These act as control links for comparing results over time.

• Rounding Off (Clause 0.6):

  • Final values must be rounded as per IS 2-1960 (Rules for rounding off numerical values).

• Test Setup (Clause 2.4):

  • Specimens are vertically suspended on a rectangular raft (30x5x5 cm blocks).
  • Controls (untreated specimens) placed opposite treated specimens.
  • Raft holds up to 300 blocks, allowing for large sample sizes and statistical validity.

Statistical Analysis Recommendations

• Use mean, standard deviation (σ), and coefficient of variation (CV) to analyze test results.
• Compare treated vs control groups using t-tests or ANOVA for significance.
• Maintain consistency by testing standard species each time.

Raft Design (Fig. 1 Summary)

flowchart LR
    A[Test Specimens] --> B[Preservative Treatment]
    B --> C[Installation on Raft]
    C --> D[Exposure Period]
    D --> E[Data Collection]
    E --> F[Statistical Analysis]
    F --> G[Compare with Standard Species Controls]
    G --> H[Report Results (IS 2-1960 rounding)]

For detailed preservation methods and controls, refer to IS 401-1967 and related IS codes listed in the context.

IS 6791: Preservative Treatment Standards – Key Points

Preservatives & Treatment (per IS 401-1967)

• Two standard preservatives for testing:
  • Oil type: Creosote or creosote-fuel oil (1:1)
  • Water soluble: Copper-Chrome-Arsenic (CCA) composition
• Treatment levels:
  • Creosote: 160 kg/m³ and 320 kg/m³
  • CCA: 16 kg/m³ and 32 kg/m³ (dry salt basis)

Specimen Requirements (Clause 2.3)

• For each species/tree:
  • 4 treated specimens (2 preservatives × 2 absorption levels)
  • 1 untreated specimen (control)
• Use 3 sets of similarly prepared specimens per absorption level for statistical validity.

Statistical Design (Clause 2.8.1)

• Use at least two standard species (one hardwood, one softwood) treated by the two standard preservatives for cross-time comparison.
• Apply standard statistical analysis on test results to evaluate preservative efficacy.

Summary Table: Treatment Levels

References for Detailed Methods

• IS 401-1967: Code of Practice for Preservation of Timber
• IS 2753 (Parts I & II): Estimation of preservatives
• IS 4833-1968, 4873-1968, 6341-1971, 6497-1972: Testing methods against fungi, soft rot, and durability

flowchart TD
    A[Select Timber Species] --> B[Prepare Specimens]
    B --> C[Treat with Preservatives]
    C --> D[Creosote @ 160 & 320 kg/m³]
    C --> E[CCA @ 16 & 32 kg/m³]
    D & E --> F[Untreated Control Specimen]
    F --> G[Install for Marine Exposure]
    G -->

IS 6791: References to Related Standards

• Rounding Off Values:
  As per IS 6791 Clause 0.6, all final test or analysis results must be rounded off following IS 2:1960 guidelines.

  • IS 2:1960 specifies the number of significant digits and rounding rules for engineering data.

• International Coordination:
  Clause 0.4 highlights that IS 6791 aligns with international standards and practices to maintain consistency and relevance.

• Supporting Institutions:
  Data contributions from the Forest Research Institute & Colleges, Dehra Dun, ensure practical relevance.

Quick Reference Table: Rounding Off (per IS 2:1960)

Summary Diagram: Standards Relationship

graph LR
A[IS 6791] --> B[IS 2:1960 (Rounding Off)]
A --> C[Forest Research Institute Data]
A --> D[International Standards Coordination]

Use IS 6791 in conjunction with IS 2:1960 for accurate reporting and rounding of test results.