Paint defects are not random - each one has a signature that points to a specific cause: pinholes say solvent, blisters say moisture, fisheyes say contamination, orange peel says viscosity or atomisation. A technician who reads the defect instead of guessing the fix solves it once.
This guide gives the diagnosis flow for the four most common paint defects on zinc hardware, with the checks in the order that finds the cause fastest.
Common Mistakes and How to Avoid Them
The pitfalls that show up most often in real projects, with the cause and the practical fix.
| Mistake | Why It Happens | Practical Fix |
|---|---|---|
| 1. Re-spraying instead of diagnosing | Same defect returns | Read the signature first |
| 2. Changing viscosity and gun together | Cause unclear | Change one variable at a time |
| 3. Blaming paint for moisture | Parts were wet | Check part dryness and RH first |
| 4. Ignoring air supply | Oil in the airline causes fisheyes | Check filters and dryers |
| 5. Short flash blamed on the oven | Pinholes come from flash, not bake | Extend flash before touching the oven |
| 6. Filtering only the first batch | Contamination returns | Filter every mix |
| 7. No test panel | Batch defects found on parts | One panel per mix |
| 8. Judging defects under poor light | Wrong diagnosis | Inspect under booth light and a magnifier |
| 9. Skipping booth hygiene | Dust specks treated as chemical | Clean booth and air filtration |
| 10. No log of defects | Same problem every week | Log defect, cause, fix |
Best Practices That Hold Up in Production
The operating disciplines that separate a reliable line from a reactive one.
- Inspect defects under good light before changing anything
- Match the signature to the cause list
- Change one variable at a time and trial
- Check part dryness and booth RH before paint chemistry
- Verify the air supply is oil- and water-free
- Filter every mix and spray through a strainer
- Run a test panel per mix
- Keep a defect log with photos
Implementation Roadmap
A practical sequence that can be adapted to your own project.
Working Data & Formula Notes
Working data - defect signatures and first checks
Each defect has a primary cause; the annotations tell you what to check before touching the paint system.
| Component / Parameter | Working Value / Role | What Changes Mean (annotation) |
|---|---|---|
| Pinholes | Trapped solvent | Flash too short or coat too thick - check flash before oven settings. |
| Blisters | Moisture under film | Check part dryness and booth RH first; then cure ramp. |
| Fisheyes | Oil / silicone / air contamination | Check airline filters, degreasing and booth air before blaming paint. |
| Orange peel | Viscosity high / poor atomisation | Thin to 16-22 s Ford #4 and raise atomisation; check gun distance. |
| Dust specks | Booth or material contamination | Clean booth, filter paint, tack-off parts. |
| Sagging / runs | Film too thick or flash short | Thinner coats and 8-12 min flash. |
Reference Data
Specifications and references cited in this guide. Confirm final parameters with your line supplier.
Defect to first check
| Pinholes | Flash time, coat thickness |
| Blisters | Part dryness, RH, cure ramp |
| Fisheyes | Air supply, degreasing, booth air |
| Orange peel | Viscosity, atomisation, distance |
| Sagging | Film thickness, flash |
| Dust | Booth, filtration, tack-off |
Diagnosis toolkit
| Magnifier / good light | Read the defect shape |
| Ford cup #4 | Viscosity check |
| Metal-temperature logger | Cure profile |
| RH meter | Moisture control |
| Test panels | Per mix |
Implementation Cases
Case 1 - pinholes that were a flash problem
Situation. A painted hardware line showed pinholes after bake; the shop blamed the oven and raised temperature, making it worse.
Approach. The diagnosis flow pointed to short flash and thick coats. Flash was extended and coats thinned.
Outcome. Pinholes disappeared without touching the oven, and flash time was added to the batch card.
Case 2 - fisheyes traced to the airline
Situation. Fisheyes appeared across all colours, and the paint was blamed repeatedly.
Approach. The airline filters were saturated - oil was reaching the gun. Filters and dryer were serviced.
Outcome. Fisheyes stopped the same shift, and the air system went on the monthly service list.
Frequently Asked Questions
What causes pinholes?
Trapped solvent popping during cure - flash time too short or coats too thick. Extend flash before changing the oven.
Why do I get blisters?
Moisture under the film. Check part dryness and booth RH before touching the paint.
What are fisheyes and why do they appear?
Small craters from oil, silicone or contaminated air. Check the airline, degreasing and booth air.
Why does my paint look like orange peel?
Viscosity too high or poor atomisation. Thin to the cup window and raise atomisation pressure.
How do I diagnose a defect quickly?
Classify it, check the obvious (dryness, RH, air), then the mix, then the gun, then flash and cure - one variable at a time.
Should I filter paint every batch?
Yes. Contamination returns if only the first batch is filtered.
Why do defects return after re-spraying?
Because the cause was not fixed. Log the defect and the cause, not just the rework.
How do I tell dust from chemical defects?
Dust is random, embedded specks; chemical defects follow a pattern. A magnifier and good light settle it.
What is the cheapest prevention?
Part dryness, booth hygiene, filtered air and a Ford cup check - they prevent most defects before they start.
Who can help with a stubborn defect?
Paint process engineers can review photos, batch cards and booth data and pinpoint the cause - send a clear defect photo.
What Would You Like to Solve?
Every paint defect has a signature. If you send a close photo of the defect and the batch card, we can help you classify it and tell you which check - dryness, air, mix, gun or flash - to run first.
Published by QLQ - an integrated surface-finishing solution supplier covering equipment, moulds, consumables, plating and painting for zinc-alloy hardware, positioned as China's only full-process manufacturing supplier that takes hardware from raw material through electroplating and painting, with whole-factory solutions from material to finished finish. Values cited are project references; confirm with your line supplier before specification.