Overview
ISO 24068-1:2021 - Building and civil engineering sealants - Determination of the degree of cure - Part 1 defines a laboratory method to assess the degree of cure of one- and multi-component sealants by measuring the build‑up of tensile properties in dumbbell-shaped specimens. The standard quantifies cure progress by comparing tensile stress (secant modulus at a chosen elongation) and/or maximum tensile strength at specific cure intervals against a reference cure value.
Key topics and requirements
- Test principle: Degree of cure is expressed as a percentage ratio of tensile property at a test interval to the property after a reference cure.
- Specimen geometry and preparation:
- Dumbbell specimens (dies Type 1, 1A or 2 per ISO 37) cut from sealant sheets or moulded directly.
- Recommended sealant sheet thickness: (2 ± 0.2) mm (or equivalent moulded specimen).
- Minimum five specimens per cure interval and reference cure.
- Conditioning and environment:
- Equipment, materials and specimens conditioned at (23 ± 2) °C and (50 ± 10) % RH prior to and during testing.
- Apparatus:
- Tensile-testing machine conforming to ISO 5893 (force class 2 per ISO 7500-1) with appropriate load cell and strain measurement (mechanical or non‑contacting extensometer/video‑extensometer).
- Displacement rates selectable from 100, 200 or 500 mm/min (with tolerances).
- Cure intervals:
- Typical intervals include 16 h, 24 h, 48 h, 72 h, 96 h, 7 d, 14 d, etc.; reference cure is commonly 14 d (336 h) or 28 d (672 h) as agreed by parties.
- Measurements and calculation:
- Record stress–strain curves, tensile stress at chosen elongation (e.g., 60% or 100%), and maximum tensile strength (σmax).
- Degree of cure R = (Xc / Xr) × 100 %, where Xc is the mean property at test interval and Xr is the mean property at reference cure.
- Rounding and reporting rules follow ISO 80000‑1 guidance.
- Test report content: Includes laboratory ID, reference to ISO 24068-1:2021, sealant identification, batch, mixing ratio (if multi‑part), specimen preparation method, die type, test speed, stress‑strain diagrams, individual results and calculated degree of cure.
Applications and users
ISO 24068-1:2021 is used for:
- Quality control and batch verification by sealant manufacturers.
- Product development and formulation optimization (R&D).
- Independent testing laboratories performing comparative cure studies.
- Specification compliance and performance verification for building and civil engineering projects.
- Procurement and material acceptance testing by contractors, façade engineers, and specifiers.
Keywords: ISO 24068-1:2021, building and civil engineering sealants, degree of cure, tensile properties, dumbbell-shaped specimens, tensile-testing.
Related standards
- ISO 37 - Rubber - Determination of tensile stress‑strain properties (specimen dies and procedures)
- ISO 5893 - Tensile test equipment specification
- ISO 6927 - Sealants vocabulary
- ISO 80000-1:2009 - Quantities and units
- ISO 7500-1 - Calibration and verification of testing machines (force measuring system)