When a coating fails, the pattern of the failure is evidence. Diagnosing before repairing prevents repeating the same failure in the remedial work, which is a common and expensive outcome.
Blistering
Blisters filled with liquid usually indicate osmotic action: soluble salts left on the surface draw moisture through the film. This traces back to inadequate washing or salt testing before coating, discussed in our preparation guide. Blisters that are dry inside more often indicate solvent entrapment from overcoating before the previous coat released its solvent, or application over a damp substrate.
Delamination between coats
Clean separation at an interface between coats, with the underlying coat intact, points to overcoating problems: exceeding the maximum recoat interval, contamination between coats, or incompatible products. This is the failure mode discussed in our recoat interval article, and it commonly appears long after handover.
Delamination from the substrate
The whole system lifting from steel indicates preparation failure: insufficient profile, contamination, or coating applied over mill scale. On concrete it usually indicates laitance or moisture. The failure surface tells you which: clean bright metal beneath means poor adhesion from the start, while corrosion beneath means moisture or salts got underneath.
Cracking
Fine surface crazing often indicates over application, particularly in zinc silicates and intumescents which crack when applied too thickly. Cracking that follows substrate movement indicates the coating lacked flexibility for the application, common in cold stores and on movement joints.
Rust spotting
Isolated rust spots in otherwise sound coating point to pinholes, missed spots or abrasive particles embedded during blasting that later corrode. Widespread fine rusting under a thin film usually means the specified thickness was never achieved, which the records described in our DFT article would reveal.
Investigating properly
Photograph the pattern and extent before touching anything. Take samples through the full system where possible so the failure interface is visible. Review the records: preparation results, environmental logs, batch numbers, thickness measurements. Most failures are explained by a gap in those records rather than by a product defect, and identifying it prevents repetition.
MENA Industrial Supplies supplies coatings with full technical documentation and can advise on remedial specifications after a diagnosis.