- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 08 Feb 2018
Galvanisation can be used to help prevent steel from corroding. This involves coating steel in zinc. The coating of zinc prevents corrosive substances from reaching the base metal. The zinc also acts as a sacrificial anode, meaning that if the coating is scratched, the remaining zinc will still protect the exposed steel.
This form of protection may be insufficient for components exposed to acids such as acid rain, or in a salt environment, such as coastal locations, and for these applications, stainless steel is preferable.
See Stainless steel v galvanised steel for more information.
 Process of galvanisation
The typical process of galvanisation is described below.
The steel is then immersed in a flux solution. This is usually 30% zinc ammonium chloride with wetting agents, maintained at above 65°C. This helps to prevent further oxidation before the galvanising begins. The steel is then dried.
The steel is completely immersed in a bath of molten zinc. A uniform coating is produced by the zinc reacting with the steel to form a series of zinc-iron alloy layers. The mass of the steel component being protected will determine the thickness of the layers.
The component is removed from the bath after a period of immersion which varies according to the size and mass. The steel will carry with it an outer layer of molten zinc which solidifies upon cooling to form the outer coating.
Small components such as fasteners can be galvanised by a similar process. They are loaded into perforated cylindrical steel baskets and lowered into the bath. Upon removal, they are rotated at high speeds for 15-20 seconds in a centrifuge which throws off excess zinc and maintains the integrity of the components.
 Advantages of galvanised steel
There are several advantages to using galvanised steel:
- It can be more cost-effective than other protective coatings for steel.
- It has good durability and requires little maintenance.
- It has a life expectancy of more than 50 years in rural environments, and 20-25 years in more extreme urban and coastal environments.
- By fully immersing the component in zinc every part is protected, including recesses, sharp corners and inaccessible areas.
- Galvanised coatings are easily assessed by the eye.
 Disadvantages of galvanised steel
 Find out more
 Related articles on Designing Buildings Wiki
Featured articles and news
Rebuilding could take 20 to 40 years.
RSHP’s high-rise residential towers win a tall buildings award for excellence.
BSRIA study reveals strong growth in 2018.
Dame Judith Hackitt confirmed as keynote speaker – one year on from the Hackitt Report.
Save £100 on tickets.
Modern slavery in the construction sector.
What to bear in mind when claiming damages in construction.
How do we achieve sustainable clean-water infrastructure for all?
What you should know when appointing an architect.
A brief history plus some new developments.
How computational fluid dynamics (CFD) helps building design.
The Hong Kong Harbour Area Treatment Scheme (HATS).
'Expressions of interest' for construction contracts.