Quality Control
What Causes Powder Coating to Chip or Peel?
Most failures come from what happened before the powder was ever applied
By Azfar ·Technical Director
18 May 2026 7 min read powder-coating chipping peeling 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
No conversion coating on the substrate Iron phosphate on aluminium, or nothing at all on steel, leaves the surface chemically unreceptive.
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.
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 highconductivity final rinse. These cause osmotic blistering as moisture works in from the edges
Parts handled without gloves after pretreatment. Finger oils are invisible but enough to cause local adhesion failure
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.
BLISTER
Blistering Followed by Peeling
OSMOTIC FAILURE / MOISTURE-DRIVEN
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
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.
WHAT CAUSED IT
Soluble salts trapped on the substrate surface. When moisture reaches them through the
HOW TO CONFIRM IT
Look at where blistering is worst. Edge blistering spreading inward is the classic
EDGE
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
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.
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
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
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 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
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.
Ifyouhaveacoatingfailureyouaretryingtotracebacktoacause, ourtechnicalteamcan helpyouworkthroughtheanalysis. Wecanalsoauditaproductionprocesstoidentifywhere theriskofadhesionorblisteringfailureishighestbeforeitshowsupinthefield Getintouch
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