Overview - ISO 24068-2:2021 (Building and civil engineering sealants)
ISO 24068-2:2021 specifies a laboratory method for determining the degree of cure of one- and multi-component building and civil engineering sealants by measuring the build-up of tensile and adhesion properties in joint-shaped test specimens during cure. The standard defines specimen preparation, conditioning (reference and test), tensile testing, result calculation and reporting so that users can quantify how far a sealant has cured relative to a agreed reference condition.
Key topics and technical requirements
- Test specimens and substrates: Two substrate supports per specimen; substrate materials selected from mortar, anodized aluminium or glass (ISO 13640 guidance). Spacers of 12 mm × 12 mm and anti-adherent PTFE film are used for specimen assembly.
- Preparation: Sealant and components conditioned at (23 ± 2) °C and (50 ± 10) % RH for minimum 16 h prior to specimen preparation. Follow manufacturer mixing instructions for multi-component products.
- Conditioning (curing):
- Test specimens: cured at (23 ± 2) °C and (50 ± 10) % RH for selected cure intervals (typical examples: 16 h, 24 h, 48 h, 72 h, 4 d, 7 d, 14 d).
- Reference specimens: Method A - 28 days at (23 ± 2) °C/50 ± 10 % RH. Method B - Method A followed by three cycles of heat and water exposure (oven at 70 ± 2 °C and distilled water at 23 ± 2 °C).
- Tensile testing: Use a tensile-testing machine with recording device, extending specimens at (5.5 ± 0.5) mm/min until rupture. Record stress–strain curves, secant modulus at chosen elongation (e.g., 100 % or 60 %) and tensile strength (maximum stress).
- Calculations: Degree of cure (%) = (mean property of test specimens / mean property of reference specimens) × 100. Properties can be tensile stress (secant modulus) or tensile strength. Rounding rules and reporting precision follow ISO 80000-1 guidance.
- Sample size & reporting: Minimum three test and three reference specimens per condition. Test report must include specimen details, batch, mix ratio, stress–strain diagrams, conditioning methods and calculated degree of cure.
Applications and who uses it
- Sealant manufacturers: product development, cure profiling, quality control and specification compliance.
- Independent test laboratories: standardized test method for acceptance testing and comparative evaluation.
- Specifiers and contractors: verify cure performance for installation schedules, performance acceptance and warranty claims.
- R&D and formulation scientists: optimize cure rate, adhesion development and mechanical property build-up.
Keywords: ISO 24068-2:2021, building sealants, degree of cure, tensile properties, adhesion properties, test joint specimens, conditioning, tensile testing, reference specimens.
Related standards
- ISO 6927 - Sealants vocabulary
- ISO 8339 - Determination of tensile properties (extension to break)
- ISO 13640 - Specifications for test substrates
- ISO 80000-1 - Quantities and units (rounding and units guidance)