Runs, dry spray and pinholes are the cold painter's three most common rejects, and each points to a different control: film, distance or surface.
This intermediate guide maps these defects to their causes and shows the fix sequence for each.
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. Runs treated with thinner | Film cause missed | Reduce film, gauge |
| 2. Dry spray blamed on paint | Distance cause | Check distance and speed |
| 3. Pinholes blamed on booth | Surface cause | Check clean and tack |
| 4. Solvent pop ignored | Flash time | Check flash between coats |
| 5. No wet film check | Heavy film hidden | Gauge per part |
| 6. Changes in pairs | Cause unprovable | One variable per trial |
| 7. Booth conditions unlogged | Seasonal shifts | Log temperature and humidity |
| 8. No defect log | Patterns invisible | Log per batch |
Best Practices That Hold Up in Production
The operating disciplines that separate a reliable line from a reactive one.
- Gauge wet film to control runs
- Hold distance and speed to stop dry spray
- Clean and tack to prevent pinholes
- Respect flash time between coats
- Change one variable per trial
Implementation Roadmap
A practical sequence that can be adapted to your own project.
Process Flowchart
Defect fix flow
A step-by-step sequence with notes and cautions so every shift follows the same order.
- Runs follow heavy film.
- Dry spray follows distance or speed.
- Never thin below the product window.
- Booth humidity shifts seasonally.
Working Data & Formula Notes
Defect data
Reference values for cold paint defects.
| Component / Parameter | Working Value / Role | What Changes Mean (annotation) |
|---|---|---|
| Runs | Wet film too heavy | Gauge and reduce |
| Dry spray | Distance / speed | Hold the window |
| Pinholes | Surface / solvent | Clean, tack, flash |
| Booth | Temperature, humidity | Log per shift |
Reference Data
Specifications and references cited in this guide. Confirm final parameters with your line supplier.
Defect to cause map
| Defect | Likely cause | First check |
| Runs | Heavy film | Wet film gauge |
| Dry spray | Distance / speed | Booth marks |
| Pinholes | Surface / solvent | Clean, tack, flash |
| Fisheyes | Oil contamination | Gloves, clean |
Implementation Cases
Case 1 - runs that were a film problem
Situation. A painter added thinner to stop runs, but they continued; the wet film was 40% over window from overlapping passes.
Approach. Pass overlap was corrected, the film was gauged per part, and the thinner stayed in spec.
Outcome. Runs stopped; the gauge became the gate.
Case 2 - pinholes from a missed tack
Situation. Pinholes appeared across a batch; the tack cloth step had been skipped during a busy hour.
Approach. The tack step was enforced, and the prep check card was signed per part.
Outcome. Pinholes stopped; the signed card made the step visible.
Frequently Asked Questions
Why do runs happen?
Wet film is too heavy for the surface; gauge and reduce, do not over-thin.
What causes dry spray?
Gun too far or pass too fast, drying the droplets before they land.
Why pinholes?
Dust, oil or trapped solvent under or in the film.
What is solvent pop?
Solvent trapped by a fast top coat, boiling out as pinholes - respect flash time.
Why gauge film?
Runs and thin spots both hide until the defect; the gauge shows the truth.
Why one variable?
Paired changes make the defect response unprovable.
Why log booth conditions?
Humidity and temperature shift defects seasonally.
What if defects return?
Pull the log, check which variable was proven, and re-check the booth.
How do I verify the fix?
A trial part through the same conditions, checked and logged.
What Would You Like to Solve?
Tell us your paint product, booth conditions and defect photos. We can help map runs, dry spray and pinholes to the right control on your line.
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.