Overview
ISO 16862:2003 - "Paints and varnishes - Evaluation of sag resistance" defines standardized test methods to determine the sag resistance (resistance to sagging) of liquid paints, varnishes and similar coating materials when applied to a substrate held in a vertical position. The standard describes two practical approaches:
- a small-scale method using a sag index applicator on a horizontal panel that is then stood vertically, and
- a larger-scale method using a spray gun to apply coatings directly to a vertical panel.
The standard is intended for liquid coatings only and sets environmental test conditions (standard: 23 ± 2 °C and 50 ± 5 % RH) and measurement practices for wet‑film thickness and assessment of sagging during drying.
Key Topics and Requirements
- Scope and applicability: Liquid coating materials only; evaluation after application on a vertical substrate.
- Two test methods:
- Sag index applicator: drawdown stripes with defined gap blades, pre‑shear the sample, then stand panels vertically; determine the thickest stripe that shows no sag. Measure actual wet‑film thickness on a third panel (ISO 2808 referenced).
- Spray gun method: apply uniform wet film on a vertical panel, score a horizontal line and observe for filling/movement; adjust thickness and repeat to locate the maximum non‑sagging film.
- Pre‑conditioning and test environment: standard temperature and humidity per ISO 3270; attention to effect of shear rate, temperature and humidity (notably for water‑thinnable and moisture‑cure systems).
- Measurement and reporting: use wet‑film thickness gauges; report application method, substrate, film thickness, any thinner addition (as % mass/volume) and viscosity (per ISO 2884) and other relevant test conditions.
- Practical notes: comb‑type gauges give discrete steps (e.g., 25 µm increments), so sag resistance is quoted as the highest gauge value without sag.
Applications
- Quality control and production acceptance testing for coatings to ensure appearance and performance on vertical surfaces.
- R&D and formulation optimization to tune rheology and maximum applyable wet‑film thickness without sagging.
- Specification and compliance checks for coating systems used on vertical substrates (architectural, industrial, vehicle coatings).
- Process setup for spray application parameters and inspection criteria in coating operations.
Who uses this standard
- Coating manufacturers, formulation chemists, QC/test laboratories, applicators and contractors, third‑party certifiers and specifiers.
Related Standards
Normative references within ISO 16862 include: ISO 1513, ISO 1514, ISO 1517, ISO 2808, ISO 2884 (parts), ISO 3270, and ISO 15528 - all relevant for sample preparation, panels, film thickness, viscosity and test conditioning.
