When a powder coating chips or peels, the instinct is to blame the powder. Occasionally that is fair. But in our experience, the coating is telling you about a problem that existed before it was ever applied. The substrate was contaminated, the pre-treatment was incomplete, or the cure was not right. The powder just made it visible.

The Three Root Causes

Almost every chipping and peeling failure traces back to one of three things: poor surface preparation, incorrect cure, or mechanical damage after the fact. Of these, surface preparation accounts for the majority. Here is how each one presents and what actually caused it.

Adhesion

Peeling at the Interface

Adhesion failure / Pre-treatment problem

What caused it

No conversion coating on the substrate. Iron phosphate on aluminium, or nothing at all on steel, leaves the surface chemically unreceptive.
Oil or drawing compound not fully removed by degreasing. The powder bonds to the contamination layer, not the metal.
Soluble salts left on the surface from a high-conductivity final rinse. These cause osmotic blistering as moisture works in from the edges.
Parts handled without gloves after pre-treatment. Finger oils are invisible but enough to cause local adhesion failure.

How to confirm it

Cross-hatch adhesion test on a retained test coupon from the same batch. GT2 or worse tells you adhesion was borderline at time of coating.
Check DI rinse conductivity records from that production date.
Examine the underside of a peeled section. If the metal surface looks clean with no coating residue, the bond never formed. If it looks corroded under the peel, moisture was the driver.

Cure

Chipping at Impact Points

Under-cure or incorrect chemistry

What caused it

Under-cured powder has lower cross-link density, which means lower hardness and worse adhesion. Parts that look fine off the line can chip easily once in service.
Oven temperature too low or dwell time too short. Heavy parts or dense loads need longer to reach metal temperature throughout.
Hybrid epoxy polyester coating on a part that sees impact regularly. Polyester chemistry delivers better impact resistance at equivalent film build.
Film build too low, especially on edges. Under 50 microns leaves the coating vulnerable to any mechanical contact.

How to confirm it

MEK (methyl ethyl ketone) rub test on a retained sample. A well-cured coating resists 100 double rubs. Under-cured coatings soften and smear.
Pull the oven temperature logger data from that batch date. If parts ran cooler than the powder's minimum cure specification, under-cure is confirmed.
Direct impact test on a sample panel from the batch. Failure at low impact energy suggests under-cure rather than a chemistry mismatch.

Blister

Blistering Followed by Peeling

Osmotic failure / Moisture-driven

What caused it

Soluble salts trapped on the substrate surface. When moisture reaches them through the coating film, osmotic pressure builds and lifts the coating from underneath.
High-conductivity rinse water in the final stage. This is the single most common cause of blistering that appears 12 to 24 months after installation.
Inadequate conversion coating. The phosphate or zirconate layer also acts as a moisture barrier. Without it, moisture reaches bare metal directly.
Parts stored outdoors or in humid conditions before coating. Rust or flash corrosion on the surface traps moisture under the film.

How to confirm it

Look at where blistering is worst. Edge blistering spreading inward is the classic osmotic pattern. Random mid-panel blisters suggest contamination at specific points.
Pop a blister and check the liquid inside. Colourless liquid suggests osmotic pressure. Rust-coloured liquid means corrosion was already active at the interface.
Check DI rinse conductivity records. If conductivity was consistently above 50 uS/cm, soluble salt contamination is the likely driver.

Edge

Edge Chipping

Thin film at edges / Faraday cage effect

What caused it

Electrostatic powder deposition naturally thins out at sharp edges and inside corners. High gun voltage makes this worse, pushing powder away from edges rather than onto them.
Laser-cut or punched edges with no radius break are particularly prone. A sharp right-angle edge may have only 20 to 30 microns of coating versus 70 microns on the flat face.
No supplemental gun pass on critical edges during application.

How to confirm it

Measure film build at the chipped edge with a calibrated gauge or cross-section. Under 40 microns at the edge is a specification failure on most industrial standards.
If the edge shows bare metal with no corrosion underneath, it was a thin-film mechanical failure. If there is corrosion under the chip, moisture had been working through the thin film for some time.

How to Diagnose a Failure Properly

Work through these in order before drawing conclusions

Locate the failure pattern. Is it at edges, random mid-panel, around fixing holes, or spreading from a scribe line? The location tells you a lot about the mechanism.

Examine the underside of any peeled section. Clean metal means no bond formed. Corrosion means moisture got in. A powdery surface means the phosphate layer was present but weak.

Pull the production records for that batch. DI rinse conductivity, oven temperature log, and the powder batch number. If any of these are outside spec, you have found your candidate cause.

Check the film build on an unaffected part from the same batch. If it is below target, add that to your analysis. Thin film often works alongside another failure mechanism rather than causing the failure alone.

Consider what happened after delivery. Mechanical damage from handling, installation, or use in service can look very similar to adhesion failure. If the failure is perfectly circular or linear, it may be a post-delivery impact rather than a process defect.

One thing worth saying clearly: if you are seeing coating failure across multiple unrelated parts from different batches, the cause is almost certainly systemic in the production process rather than batch-specific. That is a pre-treatment or oven issue. If it is isolated to one batch, start with that batch's production records.

Factory Story

We had a run of electrical enclosures come back from a customer about fourteen months after delivery. The coating was lifting from the inside faces in several of the cabinets, following a classic blistering-then-peel pattern. We pulled the DI rinse conductivity log from that production week and found three consecutive days where the conductivity had crept up to around 80 uS/cm. The operator had recorded the readings but the threshold alarm had not been set correctly on the monitoring system, so no one had flagged it at the time. We had shipped parts with soluble salt contamination on the surface. Moisture from the installation environment had done the rest over the following year. We reset the alarm threshold, added a supervisor sign-off on DI readings above 30 uS/cm, and have not seen that failure mode since. Fourteen months is a long time to wait to find a process gap, but the records made it possible to find the exact cause within an hour of starting the investigation.

If you have a coating failure you are trying to trace back to a cause, our technical team can help you work through the analysis. We can also audit a production process to identify where the risk of adhesion or blistering failure is highest before it shows up in the field. Get in touch.

What Causes Powder Coating to Chip or Peel?

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