Overview
CEN ISO/TR 21555:2020 (ISO/TR 21555:2019) is a technical report that provides an expert overview of test methods used to evaluate the hardness and wear resistance of coatings (paints and varnishes). It is intended as a guidance document to help users select the most suitable test method for different mechanical stresses. The report summarizes common laboratory techniques, highlights method-specific considerations and points to the detailed standards that specify test procedures.
Key topics and requirements
- Purpose: overview and selection guidance rather than prescriptive, step-by-step test procedures. Detailed requirements remain in the referenced standards.
- Scope notes:
- Covers a wide range of hardness and wear-resistance methods for coatings.
- Excludes methods for testing cross-linking (wear tests in connection with solvents) and abrasion tests involving multiple impacts.
- Annex A provides a summarized list of test methods mapped to different stress types.
- Important technical considerations emphasized:
- Visco‑elastic behavior of coatings strongly affects results - timing between conditioning, testing and evaluation must be agreed and observed.
- Environmental conditions (temperature, humidity) influence mechanical properties; tests are preferably done in a climatic chamber after appropriate conditioning.
- Film thickness and operator expertise affect reproducibility and interpretation of results.
- Representative methods indexed in the report (informative list):
- Hardness (indentation): Buchholz, Knoop, Pfund, Vickers.
- Oscillation/pendulum damping: König, Persoz, rocker methods.
- Wear/resistance: single-scratch (pencils, ball stylus, conical stylus, disc, U-shaped), multiple-scratch, dry and wet abrasion tests (locked/rotating abrasive wheels, scrub tests, non‑woven web), and falling‑sand tests.
- Example numeric detail included: Buchholz indenter test uses a 500 g (~4.96 N) load for 30 s with indentation measured after 35 s (×20 microscope).
Practical applications and users
- Who uses it:
- Coating manufacturers and formulators for R&D and product development.
- Independent test laboratories and QA/QC teams for method selection and interpretation.
- Specifiers and procurement engineers choosing appropriate performance tests for applications (industrial, automotive, protective, decorative).
- Standards committees and technical authors as a reference map to related methods.
- How it helps:
- Guides selection of appropriate hardness and wear tests for specific service stresses.
- Alerts users to method limitations and factors affecting repeatability and reproducibility.
- Directs users to the normative detailed standards for execution and reporting.
Related standards
- Normative reference within the report: ISO 4618 (Paints and varnishes - Terms and definitions).
- Report prepared by ISO/TC 35 and adopted by CEN (CEN/TC 139) as CEN ISO/TR 21555:2020.
- Annex A lists the specific test standards and methods to consult for detailed procedures.