Understanding Causes of Powder Coating Chipping and Peeling Failures

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What Causes Powder Coating to Chip or Peel?

Most failures come from what happened before the powder was ever applied

By Azfar · Technical Director powder-coating

chipping

18 May 2026 peeling

7 min read

adhesion

failure-analysis

pre-treatment

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

HOW TO CONFIRM IT

No conversion coating on the substrate. Iron

Cross-hatch adhesion test on a retained test

phosphate on aluminium, or nothing at all on

coupon from the same batch. GT2 or worse tells

steel, leaves the surface chemically

you adhesion was borderline at time of coating.

unreceptive.

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Oil or drawing compound not fully removed by

Check DI rinse conductivity records from that

degreasing. The powder bonds to the

production date.

contamination layer, not the metal.

Examine the underside of a peeled section. If

Soluble salts left on the surface from a high-

the metal surface looks clean with no coating

conductivity final rinse. These cause osmotic

residue, the bond never formed. If it looks

blistering as moisture works in from the edges.

corroded under the peel, moisture was the

Parts handled without gloves after pre-

driver.

treatment. Finger oils are invisible but enough to cause local adhesion failure.

CURE

Chipping at Impact Points UNDER-CURE OR INCORRECT CHEMISTRY

WHAT CAUSED IT

HOW TO CONFIRM IT

Under-cured powder has lower cross-link

MEK (methyl ethyl ketone) rub test on a retained

density, which means lower hardness and worse

sample. A well-cured coating resists 100 double

adhesion. Parts that look fine off the line can

rubs. Under-cured coatings soften and smear.

chip easily once in service.

Pull the oven temperature logger data from that

Oven temperature too low or dwell time too

batch date. If parts ran cooler than the powder's

short. Heavy parts or dense loads need longer to

minimum cure specification, under-cure is

reach metal temperature throughout.

confirmed.

Hybrid epoxy polyester coating on a part that

Direct impact test on a sample panel from the

sees impact regularly. Polyester chemistry

batch. Failure at low impact energy suggests

delivers better impact resistance at equivalent

under-cure rather than a chemistry mismatch.

film build.

Film build too low, especially on edges. Under 50 microns leaves the coating vulnerable to any mechanical contact.

BLISTER

Blistering Followed by Peeling OSMOTIC FAILURE / MOISTURE-DRIVEN

WHAT CAUSED IT

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HOW TO CONFIRM IT

Soluble salts trapped on the substrate surface.

Look at where blistering is worst. Edge

When moisture reaches them through the

blistering spreading inward is the classic

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coating film, osmotic pressure builds and lifts

osmotic pattern. Random mid-panel blisters

the coating from underneath.

suggest contamination at specific points.

High-conductivity rinse water in the final stage.

Pop a blister and check the liquid inside.

This is the single most common cause of

Colourless liquid suggests osmotic pressure.

blistering that appears 12 to 24 months after

Rust-coloured liquid means corrosion was

installation.

already active at the interface.

Inadequate conversion coating. The phosphate

Check DI rinse conductivity records. If

or zirconate layer also acts as a moisture barrier.

conductivity was consistently above 50 uS/cm,

Without it, moisture reaches bare metal directly.

soluble salt contamination is the likely driver.

Parts stored outdoors or in humid conditions before coating. Rust or flash corrosion on the surface traps moisture under the film.

EDGE

Edge Chipping THIN FILM AT EDGES / FARADAY CAGE EFFECT

WHAT CAUSED IT

HOW TO CONFIRM IT

Electrostatic powder deposition naturally thins

Measure film build at the chipped edge with a

out at sharp edges and inside corners. High gun

calibrated gauge or cross-section. Under 40

voltage makes this worse, pushing powder away

microns at the edge is a specification failure on

from edges rather than onto them.

most industrial standards.

Laser-cut or punched edges with no radius

If the edge shows bare metal with no corrosion

break are particularly prone. A sharp right-angle

underneath, it was a thin-film mechanical

edge may have only 20 to 30 microns of coating

failure. If there is corrosion under the chip,

versus 70 microns on the flat face.

moisture had been working through the thin film

No supplemental gun pass on critical edges

for some time.

during application.

How to Diagnose a Failure Properly Work through these in order before drawing conclusions 1

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.

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2

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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.

3

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.

4

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.

5

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.

FA C TO RY S TO RY

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.

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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.

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