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How to protect steel from rust: coatings, galvanizing and surface preparation
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Short answer
Protection starts with surface preparation: removing mill scale, rust and grease, ideally by blast cleaning. Then either a paint system of primer, intermediate and topcoat, or hot-dip galvanizing. In coastal or very humid locations, galvanizing plus paint (a duplex system) gives the longest life.
Step one: surface preparation
Most coating failures come from poor surface preparation. Mill scale, rust and grease must be removed. Blast cleaning to Sa 2½ is the benchmark for important work; hand or wire-brush cleaning is acceptable only for minor work.
Choose the system for the environment
| Environment | Suggested protection |
|---|---|
| Dry interior | Primer and topcoat |
| Urban or industrial exterior | Zinc-rich primer, epoxy intermediate, polyurethane topcoat |
| Coastal or high humidity | Hot-dip galvanizing plus paint (duplex) |
Tips that extend life
- Touch up coating at site welds and cuts straight away
- Avoid details that trap water and add drain holes in closed sections
- Inspect periodically and repair scratches before rust spreads
FAQ
Is galvanizing better than paint?
Hot-dip galvanizing protects inside and out and lasts many years without maintenance, but is done before erection. Paint is more flexible and comes in many colours. Together they are strongest in harsh environments.
General guidance — not an offer or commitment by BUILDORA.