ISO 6238:2018

Overview

ISO 6238:2018 specifies a laboratory method for determining the shear strength of wood‑to‑wood adhesive bonds using a standard specimen loaded in compression. The standard covers specimen preparation, conditioning, testing using a compressive shearing tool, data expression and reporting. It is intended for testing adhesives used to bond wood to wood and is not intended for testing manufactured products.

Key topics and technical requirements

• Scope and intent: Test method for adhesives used in wood-to-wood bonding; excludes finished product testing.
• Test specimens: Two specimen geometries are defined:
  • Specimen A: bonded area 40 mm × 50 mm, thickness T = 20 mm (use in case of dispute).
  • Specimen B: bonded area 25 mm × 25 mm, thickness T = 10 mm.
• Specimen quantities:
  • Minimum for routine quality control: 3 test joints from each of 3 bonded blocks.
  • For greater precision: 5 test joints from each of 4 bonded blocks.
• Apparatus and calibration:
  • Accurate balances, spreaders, presses or clamps, and a tensile-testing machine operated in compression with a self‑aligning shearing tool.
  • Force-measuring system accuracy ±1 %; machine verification per ISO 7500‑1.
• Preparation and conditioning:
  • Blocks knife-planed for flat, parallel bonding faces; adhesive applied per manufacturer’s recommendations.
  • Conditioning at (50 ± 5) % relative humidity and (23 ± 2) °C for 7 days or until constant mass.
  • Annex A lists manufacturer-supplied variables required prior to testing (moisture content, spread rate, assembly, compression conditions, etc.).
• Test procedure and data:
  • Apply continuously increasing force so failure occurs within (60 ± 20) s.
  • Record force at break (kN) and estimate percentage wood failure using oblique illumination; evaluate both fracture faces to nearest 10 %.
  • Calculate mean and standard deviation for force/stress and wood failure; report results and test details per Clause 11.

Applications and users

• Practical uses:
  • Adhesive manufacturers for product development and quality control.
  • Test laboratories performing standardized shear strength testing on wood adhesives.
  • R&D teams in woodworking, timber engineering and composite wood product development validating bond performance.
• Value:
  • Provides reproducible, comparable shear strength data for specification, acceptance testing and benchmarking of wood-to-wood adhesives.

Related standards

• ISO 291 - Standard atmospheres for conditioning and testing.
• ISO 7500‑1 - Verification and calibration of force‑measuring systems in testing machines.

Keywords: ISO 6238:2018, wood-to-wood adhesive bonds, shear strength, compressive loading, adhesive testing, bondline, specimen geometry, conditioning.