Seasoning of timber- Code of practice

IS 1141: Scope - Key Specifications & Tables

IS 1141 primarily deals with timber seasoning and moisture content control for various timber species used in furniture, construction, and special items.

Key Specifications:

• Rounding Off Values:
  Follow IS 2:1960 rules for rounding off test/analysis values, retaining significant places as per the standard.

• Moisture Content Control:
  Moisture content of timber is critical and varies by species and use.

Important Tables:

Schedule II (25 mm Planks, Species 'II') - Clause 8.4.6

Schedule V (25 mm Planks, Species 'V') - Clause 8.4.9

Related IS Codes (for detailed practices):

• IS 287: Maximum permissible moisture content of timber
• IS 401: Timber preservation
• IS 7315: Design and testing of timber seasoning kilns
• IS

IS 1141 refers to timber technology and utilization, but for definitions, it directly refers to IS 707:1976 — Glossary of terms applicable to timber technology and utilization (second revision).

Key Points on Definitions:

• All technical terms related to timber in IS 1141 follow IS 707:1976.
• IS 707 provides standardized definitions for timber species, defects, seasoning, preservation, and mechanical properties.
• This ensures uniform understanding across timber-related standards.

Important Related Standards (for comprehensive understanding):

Summary:

• Use IS 707:1976 for all timber-related definitions.
• Refer to the above standards for detailed specifications on moisture, preservation, and treatment.
• No direct formulas or tables for definitions in IS 1141; it is a reference standard.

flowchart LR
    A[IS 1141 Definitions] --> B[IS 707:1976 Glossary]
    B --> C[Timber Terms]
    B --> D[Seasoning]
    B --> E[Preservation]
    B --> F[Mechanical Properties]

IS 1141: Classification of Timbers for Seasoning

Key Points:

• Seasoning Methods (Clause 8.1):

  • Air seasoning
  • Kiln seasoning

• Stacking Practice (Fig. 6): Horizontal stacking with:

  • Wooden beams for weight
  • Crossers in vertical alignment
  • Gaps for air circulation between planks
  • Removable samples for drying rate determination

Kiln Schedule Example (Clause 8.4.6, Schedule II for 25 mm thick planks, Species marked 'II')

Summary:

• Timbers are classified based on species and usage for seasoning.
• Air seasoning involves natural drying with controlled stacking.
• Kiln seasoning uses controlled temperature and humidity as per schedules like Schedule II.
• Proper stacking and airflow are critical to avoid defects like warping.

flowchart LR
    A[Timber Classification] --> B[Air Seasoning]
    A --> C[Kiln Seasoning]
    C --> D[Schedule II]
    D --> E{Moisture Content}
    E -->|Green| F[45°C, 40°C, 72% RH]
    E -->|60%| G[47°C, 40°C, 64% RH]
    E -->|40%| H[49°C, 40°C, 56% RH]
    E -->|30%| I[53°C, 40°C, 44% RH]
    E -->|20%| J[58°C, 40°C, 32.5% RH]

Use this schedule and stacking guidelines to optimize seasoning and minimize defects.

IS 1141: Preliminary Treatment and Storage of Timber - Key Points

1. Chemical Treatment for Dimensional Stability

• PEG-1000 Concentration Formula (Clause A-1.3):
  The minimum concentration of polyethylene glycol (PEG-1000) solution for near-complete dimensional stabilization depends on wood specific gravity (SG).
  [ \text{PEG concentration} \propto \text{Specific Gravity of wood} ]
  (Exact formula details are in IS 1141 Annex A-1.3)

2. Storage and Stacking (Clause 6.3)

• Logs should be:
  • Debarked
  • Stacked on raised cement-concrete platforms
  • Subjected to continuous or intermittent water sprays
  • Platforms must collect drained water into a reservoir with:
    • Pipes
    • Centrifugal pump
    • Spray nozzles for water recirculation
• Water may contain preservatives/insecticides or be replaced regularly.

3. End Coating to Prevent Splitting (Clause 6.3)

• Coat ends up to 80 mm with moisture-proof compositions:
  • Thick coal tar
  • Rosin and lamp black (10:1)
  • Hardened gloss oil
  • Paraffin wax

4. Prophylactic Treatment (Clause 8.2.3)

• Apply preservative treatments conforming to IS 401:1982 to protect against insects and decay during storage and seasoning.

Summary Table: End Coating Materials

flowchart TD
    A[Logs Debarked] --> B[Stacked on Raised Platform]
    B --> C[Water Spray System]
    C --> D[Water Reservoir with Pump & Nozzles]
    D --> C
    B --> E[End Coating (80

IS 1141 – Defects for Seasoning Purposes: Key Points

1. Classification of Defects (Clause 5.1)

• Drying Defects: Develop during the seasoning process due to moisture loss.
• Defects Not Associated with Drying: Present in the living tree or caused during felling.

2. Examples of Defects Not Associated with Drying (Clause 5.3)

• Knots
• Heart and Cup Shakes
• Pith
• Brittle Heart
• Pitch Pockets
• Sloping, Wavy, or Spiral Grain
• Warping on the saw or splitting ahead of the saw (due to residual growth stresses)

These defects cannot be eliminated but damage can be minimized by proper sawing and seasoning techniques.

3. Inspection Criteria (Clause 12.1)

• Moisture content
• Residual case hardening stresses (if necessary)
• Natural and seasoning defects

Summary Table of Defects

flowchart TD
    A[Timber Defects] --> B[Drying Defects]
    A --> C[Non-Drying Defects]
    C --> D[Knots, Shakes, Pith, Grain Irregularities]
    C --> E[Residual Growth Stresses]
    E --> F[Warping, Splitting]

For detailed timber classification, refer to Annex B of IS 1141. Proper seasoning and sawing minimize defect impact.

IS 1141: Key Specifications & Practices for Stacking Timber

1. Stacking Supports (Clause 2.5 & 1.2)

• Crossers: 50 mm × 40 mm, spaced at 2.5 m intervals.
• Stack Height: Up to 3 m.
• Stack Width: Max 2.0 m.
• Vertical Pillars: 3000 mm² cross-section, height 300–450 mm, spaced 1.2 m c/c.
• Spacing Between Units: Minimum 750 mm for air circulation.
• Align gulleys with prevailing wind for ventilation.

2. Stack Formation (Clause 6.5 & 8.3.2.3)

• Stack sides must be plane and vertical with no projecting edges.
• Fill entire stacking space length and height.
• Use baffles to block gaps preventing air short-circuit.
• Top layers weighted to prevent warping.
• Randomly distribute gaps between timbers to ensure uniform airflow.

3. Moisture Protection

• Ends covered with moisture-proof composition (see Clause 6.3).

4. Stacking Methods (Figures 1-5)

• One-and-Nine Stacking
• Close Crib Stacking
• Open Crib Stacking
• Stack of Poles
• Stack of Fence Posts

Summary Table: Stacking Dimensions

flowchart TB
    A[Start: Timber Stacking] --> B[Place Vertical Pillars (1.2 m c/c)]
    B --> C[Set Crossers (50x40 mm) every 2.5 m]
    C --> D[Stack Timber (

Moisture Content of Seasoned Timber (IS 1141 referencing IS 287:1993 & IS 11215:1991)

• Final Moisture Content (MC) depends on:

  • Service requirements (e.g., indoor furniture vs. outdoor use)
  • Climatic zone of use (India divided into 4 climatic zones per IS 287:1993)

• Typical Moisture Content Ranges:

  Use Type	Moisture Content (%)	Remarks
  High-class indoor	10 - 12	For cabinet work, panelling, etc.
  Rough/outdoor work	15 - 25	Allows easier preservative treatment

• Seasoning Guidelines (Clause 8.4.2):

  • For 25 mm thick timber: Use specified temperature & humidity schedules (IS 1141 Schedules I–VII).
  • For 25–50 mm thick timber: Increase relative humidity by 5% at each seasoning stage.
  • For 50–100 mm thick timber: Preliminary air seasoning to ~25% MC, then kiln drying with humidity as for 50 mm timber.

• Moisture Content Determination: As per IS 11215:1991 (oven-dry method, electrical moisture meters, etc.).

Summary Formula for Moisture Content (MC):

[ MC% = \frac{W_{wet} - W_{dry}}{W_{dry}} \times 100 ]

Where:

• (W_{wet}) = weight of timber before drying
• (W_{dry}) = oven-dry weight of timber

flowchart LR
    A[Freshly Felled Timber] --> B[High Moisture Content (~100-200% MC)]
    B --> C[Air Seasoning (reduce to ~25% MC)]
    C --> D[Kiln Drying (reduce to 10-12% MC for indoor use)]
    C --> E[Use at 15-25% MC for outdoor/rough work]

References:

• IS 287:1993 (Moisture content limits by climatic zones)
• IS 11215:1991 (Moisture content determination methods)
• IS 1141 Clause

IS 1141: Seasoning Methods Key Points

1. Air Seasoning (Clause 8.2)

• Natural drying of timber by exposing it to air.
• Slower process but economical.
• Requires proper stacking and ventilation to avoid decay and warping.

2. Chemical Seasoning (Clause 10.1 & 10.1.2)

• Uses chemicals to accelerate drying and prevent defects.
• Common chemicals/compositions:

3. Precautions (Clause 10.2.2)

• Chemical pretreatment can increase warping and collapse during kiln drying.
• Preliminary trials are essential for each timber species.

Summary Diagram: Seasoning Methods Flow

flowchart TD
    A[Timber Seasoning] --> B[Air Seasoning]
    A --> C[Chemical Seasoning]
    C --> D[Polyethylene Glycol]
    C --> E[Urea Solution]
    C --> F[Urea-Sorbitol Solution]
    C --> G[Preliminary Trials Required]

Use chemical seasoning cautiously, balancing cost and timber species behavior.

IS 1141: Kiln Seasoning & Kiln Operation - Key Points

1. Kiln Seasoning (Clause 8.3 & 8.4.1)

• Kiln drying starts at lower temperature and higher humidity to avoid timber defects.
• The drying schedule controls temperature and relative humidity (RH) for effective seasoning.

2. Kiln Drying Schedule (Clause 8.4.7, Schedule III)

• Applies to 25 mm thick planks of species marked 'III' (light furniture timber).
• Drying conditions vary with moisture content of the wettest timber on the air inlet side.

3. Practical Notes

• Maintain gradual increase in dry bulb temperature.
• Keep wet bulb temperature close to dry bulb initially to avoid surface checking.
• Control RH to slow down moisture loss as timber approaches target moisture content.

flowchart LR
    A[Start: Green Timber] --> B{Check Moisture Content}
    B -->|>60%| C[Set Temp: 42°C DB, 38°C WB, RH 76%]
    B -->|40-60%| D[Increase Temp Gradually]
    D --> E[Adjust RH Lower]
    E --> F[Final Drying at 55°C DB, 40°C WB, RH 39%]
    F --> G[End: Seasoned Timber]

This table and schedule help optimize kiln operation for quality timber seasoning per IS 1141.

IS 1141: Pre- and Post-Treatment Seasoning Key Points

1. Pre-Treatment Seasoning (Clause 10.2.2)

• Pre-treatment can reduce drying time but may increase warping and collapse in kiln drying for some species.
• Requires careful preliminary trials before commercial adoption.

2. Saw-Dry-Rip Procedure (Clause 10.3.3)

• Used for species with severe growth stresses (e.g., Populus deltoides, Hevea brasiliensis, Eucalyptus grandis).
• Steps:
  • Flat saw logs into full-width thick flitches.
  • Season flitches (air or kiln).
  • Finally convert flitches into final cut sizes.
• Benefits:
  • Larger flitch dimensions help reduce internal stresses.
  • Rapid kiln seasoning at high temperature may be effective without increasing degrade in some species.

3. Air Seasoning (Clause 8.2)

• Conventional method, slower but energy-efficient.
• Often used before kiln seasoning or for species sensitive to rapid drying.

Summary Table: Seasoning Methods & Effects

Conceptual Diagram: Saw-Dry-Rip Process

flowchart LR
    A[Log] --> B[Flat Saw into Thick Flitches]
    B --> C[Season Flitches (Air/Kiln)]
    C --> D[Convert to Final Cut Sizes]

Note: IS 1141 emphasizes trials and species-specific approaches to minimize defects and optimize drying efficiency.

IS 1141: Inspection and Testing - Key Points

• Rounding Off Results:
  Test or analysis results must be rounded off per IS 2:1960 rules, retaining the same number of significant figures as specified values.

• Moisture Content:
  Seasoned timber must conform to moisture content limits per IS 287:1993. Moisture affects durability and strength.

• Inspection Parameters:

  • Moisture content
  • Residual case hardening stresses (where applicable)
  • Natural and seasoning defects

• Testing Procedures:

  • Final check tests on kiln samples as per Annex D (Clauses 8.3.2.10, 8.3.2.13, 12.4)
  • Cutting test sections from kiln charges for evaluation

• Relevant IS Codes for Testing & Preservation:

  IS No.	Title
  287:1993	Max permissible moisture content of timber
  401:1982	Timber preservation practices
  11215:1991	Moisture content determination methods

Summary Table: Moisture Content Limits (IS 287:1993)

flowchart TD
    A[Timber Sample] --> B{Inspection}
    B --> C[Moisture Content Check]
    B --> D[Check for Defects]
    B --> E[Residual Stress Measurement]
    C --> F{Within Limits?}
    D --> F
    E --> F
    F -->|Yes| G[Accept Timber]
    F -->|No| H[Reject or Reprocess]

Note: Follow IS 1141 and referenced IS codes strictly for consistent quality and durability of timber products.

IS 1141: Transport and Storage of Seasoned Timber – Key Points

Transport (Clause 13.2)

• Stacking: Seasoned timber must be transported in close stacks.
• Protection: Use covered wagons or cover stacks with tarpaulins to protect against rain.
• Special Timber: Seasoned half-wrought timber for special use should be packed in gunny bags.

Storage (Clause 13)

• Store timber in a dry, well-ventilated place to prevent moisture absorption.
• Inspect for natural and seasoning defects as per Clause 12.5 before storage.
• Stack timber with stickers (spacers) between layers for air circulation.

Kiln Drying Schedule (Clause 8.4.6, Table)

For 25 mm thick planks (Species marked 'II'):

Summary Diagram: Transport & Storage Flow

flowchart TD
    A[Seasoned Timber] --> B[Inspection for Defects]
    B --> C{Transport}
    C -->|Close Stacks| D[Covered Wagons / Tarpaulin]
    C -->|Special Timber| E[Gunny Bags]
    B --> F[Storage]
    F --> G[Dry, Ventilated Area]
    F --> H[Stack with Stickers]

Note: Follow kiln schedules strictly to achieve desired moisture content and minimize defects during seasoning and storage.

IS 1141: Glossary of Terms & Key Specifications

• Glossary Reference: Definitions related to timber technology and utilization are as per IS 707:1976 (Second Revision).

• Related Standards:

  IS No.	Title
  287:1993	Max permissible moisture content of timber
  401:1982	Timber preservation code
  707:1976	Glossary of timber terms (key reference)
  6313 (Part 2):1981	Anti-termite chemical treatment
  7315:1974	Timber seasoning kiln guidelines
  11215:1991	Moisture content determination methods

• Kiln Schedule V (for 25 mm thick planks of species marked 'V' in Annex B):

• Usage: This schedule guides kiln drying parameters for specific timber species ensuring quality and durability.

flowchart LR
    A[Timber Species 'V'] --> B[Kiln Drying]
    B --> C{Moisture Content}
    C -->|Green 42%| D[42°C Dry, 38.5°C Wet, 80% RH]
    C -->|15%| E[55°C Dry, 40°C Wet, 39% RH]
    D --> F[Quality Timber for Furniture/Construction]
    E --> F

Summary: Use IS 707:1976 for terminology; follow kiln schedules (Table above) from IS 1141 for drying timber species

Classification of Indian Timbers Based on Seasoning Behaviour (IS 1141)

IS 1141 classifies timbers into three seasoning behaviour classes (Annex B):

1. Easy to Season
2. Moderately Difficult to Season
3. Difficult to Season

Key Points:

• Classification depends on how timbers react to drying (e.g., warping, checking, splitting).
• Annex B lists commercially important Indian timbers under these classes.
• Final moisture content depends on service conditions and climatic zones (refer IS 287:1993).
• Moisture content limits and tolerances are standardized in IS 287:1993.
• Moisture content determination methods are in IS 11215:1991.

Moisture Content Limits (from IS 287:1993) Summary:

References for Seasoning & Preservation:

• IS 287:1993 — Moisture content limits
• IS 401:1982 — Timber preservation
• IS 7315:1974 — Kiln seasoning guidelines
• IS 11215:1991 — Moisture content determination

flowchart LR
    A[Indian Timbers] --> B[Classification by Seasoning Behaviour]
    B --> C[Easy to Season]
    B --> D[Moderately Difficult]
    B --> E[Difficult to Season]
    C --> F[Annex B - Timber List]
    D --> F
    E --> F
    F --> G[Final Moisture Content per IS 287]
    G --> H[Service & Climatic Conditions]

This classification helps in selecting proper seasoning methods and predicting drying defects.

IS 1141: Kiln Sample Selection and Testing Procedures

1. Kiln Sample Selection (Clause 8.3.2.5)

• Select samples from thickest, wettest, slowest drying stock in kiln charge.
• Prefer heartwood over sapwood due to slower drying.
• Use these samples to select and regulate drying schedules.
• If mixed stock with varied moisture/drying times exists, keep extra samples of driest and fastest drying pieces for monitoring only (not for schedule regulation).

2. Kiln Sample Preparation (Clause 8.3.2.6)

• Samples should represent the most difficult-to-dry stock.
• Follow guidelines in Annex B for refractoriness and drying schedules.

3. Final Check Tests on Kiln Samples (Clause 8.3.2.13, Annex D)

• Conduct cutting of test sections after drying to check moisture content and quality.
• Use results to verify drying effectiveness before dispatch.

4. Kiln Drying Schedules (Clause 8.4)

• Drying schedules must be based on kiln samples’ moisture content and drying characteristics.
• Adjust temperature, humidity, and airflow per sample data.

Summary Table: Sample Selection Criteria

flowchart LR
    A[Kiln Charge] --> B[Select Thickest, Wettest, Slowest Drying Samples]
    B --> C[Use for Drying Schedule & Regulation]
    A --> D[Select Driest, Fastest Drying Samples]
    D --> E[Monitor Moisture Content Only]
    C --> F[Adjust Kiln Conditions]
    F --> G[Final Check Tests (Cut Test Sections)]

This ensures optimal drying control and quality assurance per IS 1141 requirements.