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The Ultimate Guide: Hot-Dip Galvanising

in Steel building, Category
3 Nov 2017

The History of Hot-Dip Galvanising

The first record of hot dip galvanising steel seems to have been in France in 1742 by Chemist Paul Jacques Malouin.

 hot dip galvanising steel 


 What Is Hot-Dip Galvanising?

Hot-dip galvanising is a form of galvanisation (no surprise there) which is the process of coating iron or steel with a layer of zinc. The metal is immersed into a bath of molten zinc at temperatures of 445°C to 465°C.


How Does It Work?

Hot-dip galvanising steel (aka HDG) prevents corrosion in three ways:

1.       Barrier Protection. Zinc metal is so dense that no electrolytes such as rainwater can penetrate the coating meaning the base steel will not corrode.

2.       Cathodic Protection. When the coating is damaged in the presence of an electrolyte the zinc gives up electrons to protect the steel, providing a sacrificial coating. So, as long as there is zinc on the surface, the steel will be protected.

3.       Patina Protection. When the galvanising process is complete and the zinc metal is exposed to the oxygen in the air, it will react with the oxygen to form zinc hydroxide. Over time as the zinc hydroxide is exposed to moisture in the air a thin layer of zinc carbonate forms. This is a passive patina film that is tightly bound to the zinc of the galvanised coating and is what makes a HDG coating so durable.

DID YOU KNOW in 1772, Italian, Luigi Galvani, galvanising’s namesake, discovered the electrochemical process that takes place between metals during an experiment with frog’s legs?


What Are the Benefits?

Lowest long-term cost

  • Although the lower initial cost of other commercial coatings such as paint will often be tempting, when you compare the longevity of each coating it is obvious that hot-dip galvanising comes out on top. HDG steel will not require maintenance for over 100 years so it does not need the time, money and labour spent on constant ‘touching up’ that a painted frame would. In other words, a HDG coating is the most cost-effective coating over the long-term.

DID YOU KNOW unprotected steel will corrode 10 – 40 times faster than HDG steel, depending on the environment?

Lowest maintenance

  • Zinc’s cathodic protection means that if small areas of steel are exposed by impact or abrasion they will still be protected. So, unlike other coatings, HDG does not need small damaged areas to be touched-up or repaired.

Toughest coating

  • The metallurgical structure of HDG provides durability and resistance to damage from transport, erection and service.

Complete protection

  • When steel is immersed into the bath of molten zinc it means that every part is protected, even recesses, sharp corners and inaccessible areas



What happens if the zinc coating on my shed frame is damaged? Will the exposed steel rust?

No. One of the ways that zinc coating protects steel is through cathodic protection. When the zinc coating is damaged in the presence of an electrolyte such as rainwater, a galvanic cell is created. Because zinc is more anodic than steel, it readily gives up electrons and acts as a sacrificial coating. The surface is quickly covered, preventing corrosion. 

How long does galvanising steel add to its lifespan?

According to the American Galvanisers Association, in a rural environment, steel with an average of 3.00 mil of zinc coating will not need maintenance for 100 years! In an industrial environment, they suggest over 70 years.

Is hot dip galvanising abrasion resistant?

The toughness of a galvanised coating makes it suitable in situations where abrasion could be a problem. Even when base steel is exposed the sacrificial corrosion protection properties of a galvanising coating will protect these exposed areas and prevent unsightly and damaging rust.

How do I care for and maintain hot-dip galvanised steel?

Galvanised steel is very easy to maintain, and can be done by simple washing down with water.

Avoid abrasive washing of your galvanised product because it can remove the protective patina film (we mentioned this earlier) and the galvanised steel has to build up this barrier protection again.  


 “Building solutions today, covering the challenges of tomorrow”

At Action, we deliver a shed that you can be confident will stand the test of time. How? On an Action shed, both the columns and trusses are fully hot-dip galvanised, ensuring a very durable and long-lasting asset.


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