Steel structure manufacturer since 2009 · 8 fabrication bases in China
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Coating and fire protection, chosen for the site and fixed before fabrication
A coating is specified by two things: how aggressive the site is, and how long it must last before first maintenance. Fire protection is specified by the rating and the section. All three must be fixed before shop drawings, because they change the details.
ISO 12944
Paint system standard
ISO 1461
Galvanizing standard
Sa 2½
Blast cleaning grade
C2–CX
Corrosivity categories
Step 1
How aggressive is the site?
ISO 12944-2 classes atmospheric corrosivity by site. Your engineer or coating consultant sets it; these are typical examples.
| Category | Corrosivity | Typical exterior | Typical interior |
|---|---|---|---|
| C2 | Low | Rural, low pollution | Unheated warehouses, possible condensation |
| C3 | Medium | Urban, mild industrial, low-salinity coast | Food plants, laundries, high humidity |
| C4 | High | Industrial, coastal with moderate salinity | Chemical plants, swimming pools |
| C5 | Very high | Industrial with high humidity, coastal with high salinity | Constant condensation, high pollution |
| CX | Extreme | Offshore, tropical with very high salinity | Extreme humidity, aggressive atmosphere |
After ISO 12944-2. Tropical coastal sites in Southeast Asia are often C4 or C5.
Step 2
How long must it last before first major maintenance?
L
Low
Up to 7 years
M
Medium
7–15 years
H
High
15–25 years
VH
Very high
More than 25 years
Durability ranges per ISO 12944-1:2017. Durability is not a guarantee period; warranties are agreed separately.
Step 3
Paint, galvanizing or both?
| Paint system | Hot-dip galvanizing | Duplex (galvanizing + paint) | |
|---|---|---|---|
| Best for | Large members, colour required, C2–C4 | Secondary steel, C3–C5, low maintenance | C5–CX, long life, colour required |
| Size limit | None | Kettle size | Kettle size |
| Damage tolerance | Low; coating scratches to steel | High; zinc protects small damage | High |
| Design changes needed | Edges and welds dressed | Vent and drain holes, symmetric details | Both |
| Relative cost | Lower for C2–C3 | Competitive at C4–C5 | Highest |
| Typical system | Zinc-rich epoxy + epoxy + polyurethane | Zinc per ISO 1461 | Zinc + sweep blast or primer + epoxy + PU |
| Steel thickness | Minimum mean zinc thickness (ISO 1461) |
|---|---|
| Over 6 mm | 85 µm |
| 3–6 mm | 70 µm |
| 1.5–3 mm | 55 µm |
| Under 1.5 mm | 45 µm |
Values for articles that are not centrifuged.
From our engineers
Galvanizing has to be designed into the drawings
Vent and drain holes. Closed hollow sections must have holes at both ends so air escapes and zinc drains. Without them, sections can burst in the bath. We place them in the shop drawings, sized per galvanizing design guides.
Kettle size sets length. A member longer than the kettle needs double dipping or a splice. Kettle size of our partner plant: to confirm.
Mixed thicknesses distort. Thin plate welded to thick plate heats unevenly and can warp. We flag such details for your engineer.
Surface preparation
Most coating failures start before the first coat
The paint brand matters less than the surface it goes on.
- Abrasive blast to ISO 8501-1 Sa 2½
- Surface profile measured per ISO 8503
- Edges rounded and welds dressed to ISO 8501-3, so paint does not pull thin
- Steel temperature at least 3 °C above dew point before each coat
- Dry film thickness per ISO 19840, measured on edges too
- Recoat intervals per the paint datasheet
Fire protection
How fire protection is specified
Intumescent coating
Thickness depends on the fire rating (R30–R120), the section factor (heated perimeter ÷ area) and the critical steel temperature. Products should carry a test assessment such as EN 13381-8 or UL 263.
Boards or spray
Often cheaper for R90–R120 and heavy sections; less tidy for exposed steel.
Concrete encasement
SRC and concrete-filled columns gain fire resistance from concrete cover.
Fix the rating before shop drawings. Intumescent thickness is calculated per section. A rating change later means re-calculation and often re-coating. Intumescent products and test reports we use: to confirm.
Transport and site
Damage happens. Plan the repair.
- Coated members separated by dunnage; lifting points wrapped
- Touch-up kit of the same system shipped with the steel
- Final top coat after erection, if you prefer to hide handling marks
- Galvanizing repair per ISO 1461 (zinc-rich paint or thermal spray)
- Photo record of coating condition at loading, so damage in transit is visible
How long will shop primer protect steel before erection?
Primer alone is a short-term protection, typically months, not years, and less in humid coastal sites. Plan the full system or the erection date accordingly.
Do you galvanize in-house?
Galvanizing is done at partner plants under our inspection; to confirm.
Which paint brands do you use?
The brand your specification names, for example Jotun, Hempel or International, with datasheets submitted for approval.
Can you paint galvanized steel?
Yes, as a duplex system, after sweep blasting or a suitable primer so paint adheres to zinc.
Who inspects the coating?
Our coating inspector at each coat; your inspector at witness points. See Quality & Inspection.
Coating proposal
Send the site location and required life
Without a specification, we propose a category, system and film thickness for your engineer to approve.