IS 1708:2014 is the Indian Standard (BIS) for methods of testing small clear specimens of timber. This standard specifies the procedures for testing small clear specimens of timber to evaluate their physical and mechanical properties. It provides standardized methods for determining moisture content, specific gravity, static bending strength, compressive strength, and other critical parameters necessary for timber grading and design.
Specifies the procedures for conducting various tests on small, clear timber specimens to determine their physical and mechanical properties.
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Subject | Test methods on small clear timber specimens | Scope |
| Tests | Static bending (MOR/MOE), compression ∥/⟂, shear, hardness | Tests |
| Moisture | Results referenced to 12 % MC (conditioning) | Method |
| Use | Establish allowable stresses for species (IS 883) | Application |
| Read with | IS 883 (timber design) / IS 1141 (seasoning) | Cross-ref |
IS 1708:2014 specifies the Methods of Testing of Small Clear Specimens of Timber. It is the mechanical-property characterisation code for timber — providing the test methods that underlie species classification, allowable design stresses, and material selection in IS 883:2016 (structural timber).
Use it when: - Specifying timber for structural use — verify mechanical properties against published values for the species - Evaluating a new / unfamiliar timber species — generate the design-strength data needed for engineering use - Testing salvaged / restoration timber — verify remaining strength after years of service - Quality control on heat-treated / fire-retardant treated timber — confirm post-treatment property retention - Forensic / failure analysis — characterise failed timber samples for legal / insurance purposes
The code covers 'small clear specimens' — defect-free, knot-free samples of standardised dimensions. The values from these tests are then 'derated' for the structural sections in actual use (which have knots, splits, density variations) per IS 883 factor tables.
Companion codes: - IS 883:2016 — Code of Practice for Design of Structural Timber - IS 287:1993 — Recommended moisture content for timber by application - IS 1141:1993 — Code of practice for seasoning of timber - IS 401:2001 — Code of practice for preservation of timber - IS 5384:1969 — Strength grouping of timbers - IS 12896:1990 — Specification for CCA preservative for timber - IS 2911 Part 2:2021 — Timber piles
IS 1708:2014 specifies methods for 18 distinct mechanical tests, including:
1. Static bending strength (Modulus of Rupture, MOR) — Clause 5: - 20 × 20 × 300 mm specimen; 280 mm span; centre load - Compute MOR = 3PL / 2bd² (MPa) at failure load - Typical values: teak 90-110 MPa; deodar 70-85 MPa; sal 100-130 MPa
2. Modulus of Elasticity in bending (E) — Clause 5: - Computed from load-deflection curve below proportional limit - E = PL³ / 4bd³δ (MPa) - Typical: teak 11-14 GPa; sal 12-16 GPa
3. Compression parallel to grain — Clause 6: - 20 × 20 × 80 mm specimen; axial load until failure - Reports maximum crushing strength (MPa) - Typical: teak 55-65 MPa; deodar 45-55 MPa; sal 65-80 MPa
4. Compression perpendicular to grain — Clause 7: - Specimen loaded across grain (radial / tangential surface) - Reports proportional limit stress (typical 8-15 MPa for hardwoods, 4-8 MPa for softwoods)
5. Tension parallel to grain — Clause 8: - Difficult test; specimen prone to end-grip failure - Reports max tensile stress; typical 80-130 MPa for tropical hardwoods
6. Tension perpendicular to grain — Clause 9: - Reports very low values (2-5 MPa typical) — wood is weak in this direction - Critical for joint design — must avoid loading in this direction
7. Shear parallel to grain — Clause 10: - Punch-shear specimen of standard geometry - Reports shear stress at failure (typical 8-18 MPa)
8. Hardness (Janka) — Clause 11: - 11.3 mm hardened steel ball pressed half-depth into specimen face - Reports load (N) — higher number = harder timber - Typical: teak 5500 N (medium-hard); sal 7800 N (hard); deodar 4500 N (medium)
9. Cleavage strength — Clause 12: - Splitting load along grain - Reports load per unit width at failure (typical 50-150 N/mm)
10. Impact bending — Clause 13: - Hammer dropped from progressively increasing heights - Reports height at which specimen breaks (gives 'toughness' rating)
Plus additional tests for nail / screw withdrawal, abrasion, etc. (Clauses 14-22).
Test specimens: standardised at 20 × 20 mm cross-section (or 50 × 50 mm for some tests); specific lengths per test. Moisture content during testing fixed at 12 ± 2% (the 'standard' moisture for property reporting).
Most critical issue: timber strength varies enormously with moisture content. Field-service timber has highly variable moisture; lab tests are at standard 12% moisture; design values come from standard-moisture results.
Strength reduction with increasing moisture (rough rules): - Modulus of Rupture: drops ~3-4% per 1% increase in moisture (until saturation around 30%) - Compression parallel: drops ~5-6% per 1% moisture increase - Shear parallel: drops ~3% per 1% moisture increase
Example: a timber with 90 MPa MOR at 12% moisture has only ~50 MPa MOR at 25% moisture (significantly compromised).
Service conditions in India: - Indoor / climate-controlled: 8-12% moisture; full design strength - Indoor / non-climate-controlled: 12-15% moisture; minor strength reduction - Outdoor sheltered: 15-20% moisture; 15-25% strength reduction - Outdoor exposed: 18-25% moisture; significant strength reduction - Below permanent waterline (fully submerged): 25-30%+ moisture; large strength reduction BUT no decay (anaerobic conditions)
For design (per IS 883): published allowable stresses are typically at 12% moisture; designer applies reduction factor for service moisture above this.
Indian standard sand and chamber for moisture conditioning: IS 1708:2014 specifies the standard humidity-controlled curing of specimens before testing. Lab equipment includes controlled-humidity chambers maintaining 65 ± 2% RH at 27 ± 2°C — gives equilibrium moisture content of 12 ± 0.5%.
1. Testing with green specimens — undried specimens give artificially low strength values. Always condition specimens to standard moisture (12%) before testing.
2. Using small-clear values directly for design — these are theoretical maxima for defect-free wood. Real structural members have knots, splits, slope of grain, density variations. Always apply IS 883 reduction factors (typically 0.4-0.7 of small-clear values).
3. Testing only one specimen — wood is highly variable. Statistical reliability requires minimum 5-10 specimens per property per species per source. Single-specimen tests are advisory only.
4. Improper grain orientation — specimens must be cut with grain direction known and aligned to load direction. Cross-grain or angled-grain specimens give intermediate (not properly characterised) values.
5. Wet specimens after preservative treatment — preservative treatment uses water-based or oil-based vehicles; treated specimens may have higher moisture content than air-equilibrated specimens. Re-condition to 12% before testing.
6. Loading rate not standardised — wood is viscoelastic; slow loading gives different strength than fast loading. IS 1708 specifies loading rates per test (typically 5-15 mm/min). Don't substitute.
7. End-grip failure on tension specimens — wood splits at the grip rather than failing in the gauge length. Use specially-designed tapered specimens or reinforced grip ends per IS 1708 Appendix.
8. Comparing values from different testing standards — IS 1708 specimen sizes differ slightly from ASTM D143 and ISO 13061. Values aren't directly comparable; convert using published conversion factors.
9. No statistical analysis — wood properties have ~20-30% coefficient of variation between specimens of same species + source. Reporting only mean values is misleading; characteristic values (5th percentile) are what's used for design.
IS 1708:2014 is the current revision (replacing IS 1708:1986), with major modernization including: - Updated specimen geometries aligned with ISO 13061 international practice - Tighter loading-rate specifications - Statistical analysis requirements - Reference to digital data-acquisition + image-analysis for measurement
Indian timber-testing reality: - Premier institutes (Forest Research Institute Dehradun, CSIR-Institute of Wood Science and Technology, ICAR institutes): publish IS 1708 test results for native and plantation species. Comprehensive databases of Indian timber properties. - University research labs: routine testing for student research; some test plantation eucalyptus / casuarina for utility-pole strength characterisation. - Industry / commercial labs: less common; specialty service for major architectural timber projects.
For specifying engineers: - For routine structural timber (teak, sal, deodar in standard sections): use published values from IS 883:2016 which incorporates IS 1708 test data - For plantation / non-traditional species (eucalyptus, casuarina, mango, jamun, etc.): commission IS 1708 testing on representative samples; develop project-specific design values - For restoration projects with salvaged timber: commission IS 1708 testing on selected specimens to verify remaining strength
Cost reality: a full set of IS 1708 tests on one species (5-10 specimens × 10-15 properties) costs ₹25,000-80,000 at a research institute; takes 4-8 weeks. Worth it for premium / structural / large-volume timber projects.
For the curious: published IS 1708 data on Indian timbers shows: - Strongest hardwoods: sal, padauk, white sirish, axlewood, indian rosewood - Premium softwoods: deodar, kail, fir - Plantation species: eucalyptus (varies by clone), casuarina, leucaena - Marginal species: most jungle / scrubland timbers
The Forest Research Institute Dehradun database of IS 1708 results is the standard reference for Indian timber engineering — accessible via FRI publications and online portals.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Static Bending Specimen (Primary) | 50 x 50 x 750 mm | 2 x 2 x 30 in (50 x 50 x 760 mm) | ASTM D143-21 |
| Static Bending Span (Primary) | 700 mm | 28 in (710 mm) | ASTM D143-21 |
| Static Bending Specimen (Secondary) | 20 x 20 x 300 mm | 20 x 20 x 360 mm | ISO 13061-3:2014 |
| Compression Parallel to Grain Specimen | 50 x 50 x 200 mm | 2 x 2 x 8 in (50 x 50 x 200 mm) | ASTM D143-21 |
| Janka Hardness Test Penetrator Diameter | 11.28 mm | 0.444 in (11.28 mm) | ASTM D143-21 |
| Shear Parallel to Grain Specimen Overall Size | 50 x 50 x 62.5 mm | 2 x 2 x 2.5 in (50 x 50 x 63 mm) | ASTM D143-21 |
| Standard Moisture Content for Reporting | 12% | 12% | ASTM D143-21 / ISO 13061-1 |