News

What is the difference between flaking and peeling coating?

A lot of terminology linked to the failure of a coating system may appear interchangeable at first sight, but the reality is that different terms are indicative of very different technical problems and need to be used properly. This is often the case in describing some common coating defects.

The failure of a surface coating can be caused by a variety of reasons at any stage in the lifecycle of a paint system.

Poor design or system formulation, inadequate surface preparation, poor application or inadequate curing can all cause problems, as well as exposure to particularly aggressive environmental conditions.

Flaking

One of the most common defects associated with coating failure is detachment – more commonly recognised as flaking, peeling or delamination.

Flaking is the result of adhesion failure, causing the paint to become separated from the substrate. It is often preceded by cracking, with the edges of the coating gradually curling away from the substrate.

Flaking is particularly familiar on timber substrates where the differential expansion between the coating and the timber can cause the separation to begin. It can also be caused by the use of an incorrect paint system, poor surface preparation or ageing of the paint system.

Flaking is similar to peeling, but with the former the coating tends to be harder and brittle. Peeling is more often associated with softer and pliable coatings and is caused by a loss of adhesion between individual coats or between the first coat and the substrate.

Typically, peeling results from a reduction in bond strength of the paint film that is caused by inadequate surface preparation, contamination between coats, exceeding maximum overcoating times or coating incompatibility.

Peeling

In many respects peeling is similar to delamination, particularly when there is contamination between coats in the form of dust, dirt, grease, condensation and chalking – all of which can disrupt proper adhesion with subsequent coats.

For those involved in paint inspections and coatings, an estimation of the degree of flaking is covered by the standards ISO 4628-5 and ASTM D772.

ISO 4628-5 assesses flaking in relation to quantity, size and depth by comparison with standard diagrams and differentiates the flaking as wither with or without a preferential direction. ASTM D772 covers the extent of flaking (or scaling) by comparison with four photographic references.

Although not designed specifically to do so, the standards can also be used as an aid to estimate the degree of peeling of delamination.

For more details see Fitz’s Atlas 2 of Coating Defects at fitzsatlas.com

Comprehensive New Guide to Protective Coating Surveys

A new guide to protective coating surveys provides comprehensive practical advice for those involved in the inspection of paint systems used for corrosion protection applications.

Fitz’s Atlas of Coating Surveys incorporates thorough practical guidance for consistent protective coating assessments and visual evaluations, and the production of detailed coating reports. It is designed to assist engineers, surveyors, inspectors and asset owners to make the correct decisions on corrosion protection and coating maintenance programmes.

Written by industry experts with many years of coatings and corrosion control experience, the new publication will enable users to make informed decisions on the management of anti-corrosion systems and coating performance.

For ease of use, the extensive guide is broken down into separate covering the essential information needed by anyone involved in undertaking surveys to establish coating condition and remedial painting specifications, review coating guarantees, or investigate coating complaints, failures and claims.

With specific reference to the marine, offshore, petrochemical, bridges and other industrial sectors, the handbook looks at common defects and explains how percentages linked to coating breakdown can be estimated, alongside full advice on approved field testing and sampling techniques.

Other technical guidance is provided on the European and International rust scale, dry film thickness, adhesion testing and porosity (holiday) detection, as well as coatings used as passive fire protection systems.

Fitz’s Atlas of Coating Surveys refers to ASTM, ISO, CEPA and SSPC standards for coating evaluation and includes the full Re Scale of Rust illustrations.

In addition, among the practical considerations covered, the guide also considers health and safety requirements, the role of photography, documentation and reporting, as well as the industry standards and test methods that should be referenced.

Fitz’s Atlas of Coatings Surveys is produced in the same pocket-sized style and format as the highly regarded Fitz’s Atlas of Coating Defects which has become a standard reference guide in the protective coatings industry.

Talk to our coatings experts today on +44 (0)7785 775 238 or ask us a question