Cold painting cannot fix a dirty surface. Dust, oil and fingerprints become pinholes, fisheyes and peeling after the paint is on.
This junior guide covers surface preparation for cold painting zinc hardware: cleaning, sanding, tack cloth and primer before the colour coat.
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. Skipping the clean | Fisheyes and peeling | Clean every part |
| 2. Sanding too coarse | Scratches show through | Per finish requirement |
| 3. No tack cloth | Dust in the film | Tack before paint |
| 4. Primer skipped | Adhesion fails | Per system spec |
| 5. Oil from hands | Fingerprint defects | Gloves |
| 6. Wet parts painted | Blush and pinholes | Dry before paint |
| 7. Booth dust | Film defects | Clean the booth |
| 8. Prep area beside booth | Dust re-contaminates | Separate prep from spray |
Best Practices That Hold Up in Production
The operating disciplines that separate a reliable line from a reactive one.
- Clean every part before sanding
- Sand to the finish requirement, not beyond
- Tack cloth as the final prep step
- Primer per the paint system
- Keep prep separate from the booth
Implementation Roadmap
A practical sequence that can be adapted to your own project.
Process Flowchart
Surface prep flow
A step-by-step sequence with notes and cautions so every shift follows the same order.
- Gloves stop fingerprint oil.
- Prep and spray must be separated.
- Never paint a wet part.
- Booth filters must be clean.
Working Data & Formula Notes
Surface prep data
Reference values for cold paint surface preparation.
| Component / Parameter | Working Value / Role | What Changes Mean (annotation) |
|---|---|---|
| Clean | Oil and dust free | Fisheyes follow oil |
| Sand | Per finish requirement | Coarse scratches show |
| Tack | Immediately before paint | Dust lands in film |
| Primer | Per system | Adhesion depends on it |
Reference Data
Specifications and references cited in this guide. Confirm final parameters with your line supplier.
Prep check card
| Step | Check | Result |
| Clean | No oil film | Water sheets |
| Sand | Grit per spec | No scratches |
| Tack | No dust | Clean cloth |
| Dry | No moisture | Ready to paint |
Implementation Cases
Case 1 - fisheyes from fingerprint oil
Situation. Cold painted locks showed fisheyes; operators handled parts without gloves after cleaning.
Approach. Gloves became mandatory after cleaning, and the tack cloth step was added before paint.
Outcome. Fisheyes stopped; the glove rule was posted at the prep station.
Case 2 - dust in film from a shared prep area
Situation. Fine dust specks appeared in the film; prep sanding was done beside the booth and dust drifted in.
Approach. Prep was moved to a separate area and the booth filters were checked weekly.
Outcome. Dust specks stopped; the separation rule became standard.
Frequently Asked Questions
Why clean before sanding?
Sanding embeds oil and dirt into the surface if it is not cleaned first.
What sanding grit?
Per the finish requirement - too coarse scratches show through the paint.
Why a tack cloth?
It is the last dust removal step; dust lands in the film seconds before paint.
Why gloves?
Fingerprint oil causes fisheyes and adhesion faults.
Why primer?
The primer is the adhesion bridge between the substrate and the colour coat.
Why dry before paint?
Moisture causes blush and pinholes in the film.
Why separate prep from the booth?
Sanding dust re-contaminates freshly prepared and painted parts.
How do I check cleanliness?
Water-sheet test, a clean white cloth wipe, and visual inspection under light.
What if I skip the tack?
Dust in the film is the most common result; never skip the final tack.
What Would You Like to Solve?
Tell us your substrate, paint system and current prep steps. We can help set the clean, sand, tack and primer sequence for your cold painting 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.