ISO 21690:2021

Overview

ISO 21690:2021 - Glass in building - Glass blocks - Specification and test methods provides standardized requirements and test methods for glass blocks used in building elements. It covers square, rectangular and circular glass blocks in three categories (hollow, dished and solid) for use in non‑load‑bearing walls and horizontally spanning panels (e.g., floors, vaults, domes). The document specifies dimensional tolerances, appearance criteria, mechanical requirements and test procedures to verify conformity.

Key topics and technical requirements

• Types and shapes: Hollow, dished and solid glass blocks; square, rectangular and circular shapes are covered.
• Dimensional tolerances: External dimensions (length, width, thickness) shall not exceed ±1.5 mm. Face thickness for hollow blocks shall be not less than 3.0 mm.
• Production irregularities: Limits for inherent irregularities - twisting or misalignment ≤ 1.5 mm, bulge ≤ 2.0 mm, depression ≤ 1.0 mm, and welded seams must be tightly sealed without protrusion beyond the edge profile.
• Appearance requirements: Visual inspection is performed at 0.8–1.0 m with backlighting (diffused source 430–540 lm/m²). Permissible blemishes are defined (e.g., bubble size thresholds, limits for opaque inclusions, scratches and pits).
• Mechanical properties:
  • Compressive strength for hollow blocks: minimum 4.4 N/mm² (test procedures in Annex A).
  • Applied load test for glass pavers (hollow, dished, solid): minimum average compressive strength 15.0 kN.
• Thermal shock resistance: For special purposes, a thermal shock test with a 40 °C temperature fall is specified; no cracks or damage permitted.
• Test methods and instrumentation: Measurement methods include sliding calipers, steel straight edges, feeler gauges; mechanical testing references include calibration and mortar capping procedures (mortar per EN 998‑2, capped layer ~10 ±2 mm).

Applications and users

ISO 21690:2021 is used to ensure consistent quality, safety and performance of glass blocks in architectural and structural installations. Typical users:

• Architects and façade designers specifying light‑transmitting partitions, non‑load‑bearing walls and glass pavements.
• Manufacturers of glass blocks for production control and product certification.
• Test laboratories and quality inspectors performing dimensional, appearance, mechanical and thermal tests.
• Building engineers and contractors verifying conformance for installation and procurement.

Related standards

Normative references cited include EN 998‑2 (masonry mortar), ISO 7500‑1 (calibration of test machines) and ISO 48‑2 (hardness testing), which are relevant for test preparation and equipment calibration.

Keywords: ISO 21690:2021, glass blocks, glass in building, specification and test methods, dimensional tolerances, compressive strength, thermal shock resistance, appearance requirements.