Also known as: Flaking, Peeling, Intercoat delamination.
What it looks like
Coating flaking or peeling away, either down to the substrate or between layers. It may come away in sheets, sometimes revealing a clean, shiny surface underneath, which is a clue to the cause.
Common causes
- Inadequate surface preparation: mill scale, rust, too little profile or the wrong preparation grade
- Contamination: oil, grease, dust, salts or condensation on the surface
- Intercoat problems: the overcoating window was missed, or the previous coat was contaminated or too glossy to bond to
- Incompatible products, such as a strong solvent coat over a sensitive primer
- Poor pretreatment before powder coating, especially on aluminium and galvanised steel
Prevention
- Specify and inspect preparation to ISO 8501-1 and ISO 8503
- Test for dust and salts, and control climate at application
- Keep within the minimum and maximum overcoating times, abrading where required
- Use products that are compatible and preferably from one system
Repair
The failed coating must be removed back to sound material, the cause corrected and the system reapplied. Adhesion testing on the remaining coating shows how far the problem extends.
Inspector’s note
Record where the failure plane is: substrate, primer or between coats. It points straight at the stage where things went wrong. See our guide to adhesion testing.