Overview
ISO 13765-3:2004 specifies a laboratory test method for determining the joint stability of refractory mortars. The standard describes how to prepare and lay mortar between refractory bricks, the apparatus and environmental controls required, and the procedure for measuring the time during which a mortar joint remains stable when one brick is moved by hand without breaking the joint. This test is used as part of quality control and product characterization in the refractory industry.
Key topics and requirements
- Scope: Method for determination of joint stability of refractory mortars.
- Referenced standards: ISO 8656-1 (sampling) and ISO 13765-1 / ISO 13765-2 (consistency via penetrating cone or reciprocating flow table).
- Apparatus and materials:
- Mixer as specified in ISO 13765-1/2.
- Electrical drying oven (110 °C ± 5 °C).
- Balance (10 kg capacity, 1 g resolution) and stopwatch.
- Spacing rods: 3 mm ± 0.1 mm diameter; measuring cylinder.
- Standard refractory bricks: 230 × 114 × 76 mm (clean, dried at least 24 h).
- Sample preparation:
- Dry mortars sampled per ISO 8656-1; reduce to 5 kg representative sample.
- Ready-mixed mortars tested “as received”; preserve supernatant liquid.
- For dry mortars, add specified water and mix; allow to stand 30 minutes (or per manufacturer).
- Test procedure:
- Apply mortar to brick face, place spacing rods 30 mm from 114 mm edges, place top brick, press and move to achieve a 3 mm joint.
- Remove rods, start stopwatch and move the top brick back and forth until the joint breaks. Record elapsed seconds.
- Perform two determinations and report the mean.
- Result reporting: Report individual times and mean, mortar identification, brick type, percentage of added water (if applicable), consistency and method used, ambient test temperature, deviations, anomalies and test date.
Applications and users
ISO 13765-3 is practical for:
- Refractory manufacturers performing product development and production quality control.
- Independent testing laboratories validating mortar performance.
- Specifiers and engineers assessing mortar suitability for installation and service conditions.
- Installers and contractors who need to confirm workability/stability windows for on-site jointing.
Keywords: refractory mortars, joint stability, ISO 13765-3:2004, mortar testing, refractory bricks, consistency test, quality control.
Related standards
- ISO 13765-1 - Consistency: penetrating cone method
- ISO 13765-2 - Consistency: reciprocating flow table method
- ISO 8656-1 - Sampling of refractory raw materials and unshaped products
This standard provides an objective, repeatable test to evaluate how long a refractory mortar remains workable and stable in a joint - essential information for manufacturing control, specification, and installation planning.