01How the process works
After abrasive blasting to the specified cleanliness and profile, primer, intermediate and topcoats are applied by airless spray, brush or roller, each within its overcoating interval. Ambient conditions (temperature, humidity, dew point) must be suitable at every stage.
Coating inspection follows a hold point sequence: surface preparation, climate, each coat's wet and dry film thickness, cure, adhesion and holidays. Most premature coating failures trace back to preparation or climate, not the paint.
- Surface preparation. Blasting to Sa 2½ and profile.
- Climate check. Steel temperature above dew point.
- Primer. Applied within the preparation window.
- Intermediate and top coats. Overcoating intervals respected.
- Final inspection. DFT, adhesion, holidays, appearance.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Poor adhesion | Contamination, surface profile | Pull-off test, cross cut |
| Low DFT | Application | DFT gauge to ISO 19840 |
| Runs and sags | Excess wet film | Visual |
| Pinholes and holidays | Application, porosity | Holiday detector |
| Amine blush | Humidity during epoxy cure | Visual, water test |
| Flash rust | Delay after blasting | Visual |
03Where an inspector should look
Before production
- Coating specification and ITP
- Product data sheets
- Inspector and applicator qualification
During production
- Cleanliness, profile, salts
- Climate readings
- WFT and recoat times
After production
- DFT survey
- Adhesion tests
- Holiday tests and repairs
04Standards and references
ISO 19840 (DFT on rough surfaces), ISO 8502 (salts, dust), ISO 8503 (profile), ISO 4624 (pull-off adhesion), NORSOK M-501.
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.