Galvanised steel windows: coatings, C5-M environments and colour 

• 28 October 2025
• News

Galvanised steel windows combine slim sightlines with robust protection, making them well suited to coastal, industrial and exposed sites. For specifiers and clients who need peace of mind around corrosion resistance, the key is the substrate and the coating system. Crittall’s galvanised steel windows are hot-dip galvanised to BS EN 1461 and finished with Duralife® polyester powder coat to deliver long-term corrosion resistance and low maintenance performance. 

What galvanisation does and why it matters

Hot-dip galvanising bonds a uniform zinc layer to the steel substrate, creating a durable barrier against corrosion. The coating thickness varies with section size and surface profile, which is an advantage because heavier sections typically develop thicker coatings as part of the process. This metallurgical bond protects the steel profile even if the outer paint is scratched, and when combined with a marine-grade polyester powder coat it produces a low maintenance exterior that resists aggressive sea salts and industrial pollution. 

Understanding C5-M and specifying for harsh weather

The ISO 12944 system is used to classify atmospheric corrosivity and to guide coating selection. The C5-M class describes very high corrosivity in marine environments where salt spray, constant condensation and heavy pollution increase the risk of rapid corrosion. For these sites, the specification should combine hot-dip galvanising with an appropriate protective paint system. 

Coatings and long-term performance

As mentioned, Crittall’s galvanised steel windows are finished with Duralife® polyester powder coat over a hot-dip galvanised substrate. That two-stage approach is proven to extend service life and keep maintenance to a minimum. For many Crittall ranges, documented life expectancy exceeds 60 years when specified and installed correctly, helping to reduce whole-life costs and energy consumption through durable, thermally efficient steel frame windows.  

It’s worth knowing that steel window and door frames have fully welded corners, allowing for continuity in the galvanising and powder coating operations. This is unlike aluminium windows, where corner mitre joints can allow the elements to penetrate, allowing corrosion to form. 

Colour choice and design flexibility

Steel window frames are available in a variety of colours to suit conservation areas and modern commercial buildings alike. Signature black steel windows remain a popular choice for their contrast and period character, while bespoke RAL and BS options allow designers to match architectural palettes. Colour sample packs and technical downloads make it straightforward to confirm finishes and hardware for high-exposure site projects, helping procurement teams and architects to convert specification into confident orders.

When you need metal windows that stand up to harsh weather conditions yet retain the slim, natural light advantages of steel profiles, galvanised steel windows with an appropriate C5-M grade coating system offer a pragmatic solution. They deliver energy efficiency, low maintenance and the proven benefits of steel for projects that must pass the test of time. For technical detail, sample packs and specification downloads contact Crittall Windows here.