ISO 9223 classifies atmospheric corrosivity from C1 (very low) to C5 (very high), and that class — not habit — should pick the coating on a solar mounting structure. Solaracks matches anodized 6005-T5 aluminium, hot-dip galvanized steel and ZAM to the site class, verifies coatings with ISO 9227 salt-spray testing, and has shipped class-matched structures to 30+ markets since 2012.
What ISO 9223 actually measures
The standard grades an atmosphere by what it does to metal — driven by time of wetness, sulphur dioxide from industry and traffic, and airborne chloride from the sea. Those three inputs place a site in one of five categories, C1 to C5. The class is a property of the site, not of the product, which is why the same racking specification cannot honestly be “right” for both a dry inland warehouse and a harbour-side plant.
The five classes, and what they mean for racking
| ISO 9223 class | Corrosivity | Typical environment | Solaracks approach |
|---|---|---|---|
| C1 | Very low | Heated interior spaces | Any standard finish exceeds the need |
| C2 | Low | Dry rural areas, low pollution | Standard anodized aluminium or HDG |
| C3 | Medium | Urban and light industrial air, low-salinity coastal | Standard range — most systems are rated C3 out of the catalogue |
| C4 | High | Industrial zones, moderate-salinity coastal | ZAM steel at 300 g/m² coating; C4-rated systems such as the ZAM ground mount |
| C5 | Very high | High-humidity industrial, high-salinity coastal | Customized higher coating standards, quoted per project |
Two catalogue facts anchor the table. Most Solaracks systems carry a C3 corrosivity category as standard, with higher classes available on request. The ZAM steel ground mount is rated C4 with a 300 g/m² coating weight — the range’s dedicated answer for aggressive sites.
The three coating routes
Anodized 6005-T5 aluminium — Rails, clamps and most rooftop components are 6005-T5 aluminium with an AA10 anodized film — ≥10 μm thickness — paired with stainless steel 304 fasteners. Aluminium’s own oxide plus the anodic layer keeps maintenance near zero across the service life, and for high-corrosion areas Solaracks produces higher film classes.
Hot-dip galvanized steel (HDG) — Structural steel such as Q235B posts and beams gets hot-dip galvanizing — a sacrificial zinc layer proven for decades in ground-mount service. HDG remains the cost-effective baseline for C2–C3 sites and for heavy sections like rammed piles and ground screws.
ZAM (zinc-aluminium-magnesium) — ZAM blends zinc, aluminium and magnesium in one coating. Compared with HDG of similar thickness, published test data shows higher corrosion resistance and better scratch resistance — and its zinc-magnesium corrosion products form a protective barrier over exposed cut edges, which matters on factory-cut and punched parts. That performance is why ZAM plays the dominant role in Solaracks ground mounting systems and waterproof carport structures.
Fasteners count too — A structure is only as protected as its smallest part. Solaracks pairs its coated structures with stainless steel 304 fasteners at 625.55 MPa ultimate strength, with TDC-coated hardware as an option — so the bolt does not become the first point of failure on a C4 site.
Microclimates move the class
ISO 9223 grades the macro-environment; a single site can still hold pockets that behave a class worse. Ground rows directly behind a coastal dune collect more salt than rows 300 m inland. A roof edge takes more spray and wind-driven moisture than its field. Livestock and fertilizer operations add ammonia around agrivoltaic structures. None of this changes the method — it changes the inputs. Name these conditions in the RFQ and the class assessment covers them, with the coating decision recorded in the engineered design rather than left to site memory.
Verified, not assumed
A class match on paper still needs proof. Solaracks coatings are salt-spray tested to ISO 9227, clamp and foot connections are pull-tested by SGS, and coating figures — AA10 film, 300 g/m² ZAM weight — appear on the datasheets with their references. The corrosion class also interacts with the structural calc: the same engineered design to AS/NZS 1170.2 / ASCE 7-22 that sizes members assumes the section keeps its thickness for the design life, which is precisely what the coating class protects. The range targets a 30-yr design life and carries a 12-yr written warranty.
How to specify it in an RFQ
State the distance to the coast, any industrial neighbours, and the country — or simply the site address. Engineering places the site in its C1–C5 class and returns the coating choice inside the engineered design and quotation within 24 hours. Ground projects choosing between aluminium, HDG and ZAM builds can compare the options under ground mounting systems; coastal rooftop projects should note the penetration-free options under roof mounting systems. Send the site through the contact page — the class costs nothing to determine and everything to ignore.
FAQ
Which corrosion class does a coastal site need? — Distance to the sea and salinity decide — moderate-salinity coastal sites typically fall in C4, where Solaracks specifies ZAM at 300 g/m², with C5 coatings customized per project. How is coating durability proven? — Coatings are salt-spray tested to ISO 9227 and documented on the datasheet, alongside SGS pull tests on the load-bearing connections. Does the corrosion class affect the warranty? — The coating is matched to the site’s ISO 9223 class inside the engineered design, and the structure carries a 12-yr written warranty on that basis.
Coatings matched to the class, in writing. — Engineered design & quote within 24 hours.