EN ISO 4628-7:2016 PDF

Overview

EN ISO 4628-7:2016 (ISO 4628-7:2016) - published by CEN - defines the velvet method for assessing the degree of chalking on exterior paints and varnishes. The method is intended mainly for rough surfaces (roughness > segment 4 of comparator G per ISO 8503‑1) and is suitable for coatings on mineral substrates such as fibre cement, brick, concrete and renderings. It is a relative, visual ranking technique recommended for laboratory and on‑site evaluation by experienced operators.

Key topics and technical requirements

• Scope & limits
  • Designed primarily for rough surfaces; for smooth surfaces ISO 4628‑6 (tape method) is preferable.
  • Applicable to white or coloured exterior coatings and coating systems on mineral substrates.
  • The method is a relative ranking and not intended as a contractual quantitative agreement unless specifically defined between parties.
• Principle
  • Loosely adherent powder (chalking) is removed from the coating using a fabric (velvet, black wool felt, velveteen for light coatings; white fabric for dark coatings). The collected powder is visually rated against a standard scale.
• Procedure highlights
  • Assessments should be made under appropriate illumination per ISO 13076.
  • Perform assessments in duplicate (unless agreed otherwise).
  • Using firm finger pressure, press the fabric against the surface, rotate 180°, remove fabric and assess under diffuse light.
  • A mechanical wiping apparatus may be used if results are comparable.
• Rating scale
  • Numerical ratings 0–5: 0 = unchanged (no perceptible chalking) to 5 = severe (intense chalking).
  • Use pictorial reference standards (comparable examples are provided and harmonized with ISO 4628‑6).
• Reporting requirements
  • Test report must identify the coating, reference ISO 4628‑7, describe surface/type/location, give numerical rating (mean, range, number of assessments), fabric used, method (finger or apparatus), deviations, anomalies, and date.

Applications and users

• Practical for quality control, R&D, weathering studies, and on‑site condition surveys of exterior coatings on masonry, concrete and similar substrates.
• Typical users: paint formulators, coatings laboratories, specifiers, façade inspectors, contractors, and asset managers who need a standardized visual method to monitor chalking and surface degradation.

Related standards

• ISO 4628‑1 - General designation system for defects and appearance changes.
• ISO 4628‑6:2011 - Chalking assessment by tape method (preferred for smooth surfaces).
• ISO 13076 - Lighting and procedure for visual assessments of coatings.
• ISO 8503‑1 - Surface roughness comparators (reference for roughness segments).

Keywords: EN ISO 4628-7:2016, ISO 4628-7, velvet method, chalking assessment, paints and varnishes, degradation of coatings, exterior coatings, rough surfaces.