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Structural steel, custom made farm and industrial sheds.

There’s More To Galvanising Than Meets The Eye

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There’s more to galvanised columns than most of us realize…

Corrosion protection is must if you want to get longevity from steel structures. That’s something we already know, particularly if we are farming near the coast and have to deal with salt-laden winds that cause everything to rust much faster.

In 1967, standards for corrosion protection were put in place, but paints and galvanising were lumped into one category. In December 2014, revised standards were published and these give us much more clarity on galvanising standards.

Different areas of the country are allocated into corrosivity categories that give us an indication of how long we can expect various thicknesses of galvanising to protect our steel structures. These areas are based on proximity to the sea shore as follows:

Corrosivity categories explained

CX: Severe surf shore line – this is the harshest environment in which we see the fastest corrosion happening.

C5: Surf seashore – here, the sea is not as rough, but salt laden winds are still a serious problem. The area is defined as being up to 200m from the seashore, but the standard notes that these conditions can extend further back from the coast depending on winds.

C4: Calm sea shore – sheltered bays with less surf provide slightly less favourable conditions for corrosion, even when buildings are sited on the shore to 50m back. Similar conditions can be found on coastlines with rougher surf and more sea spray when buildings are sited form 200m to 1km away from the shore. But as the standard notes, winds can affect this.

C3: Coastal – the sea still extends its corrosive influence for quite a distance inland. If the surf is strong, the area 1km to 10km back is still classed as ‘coastal’ and winds can carry salt-laden air as far as 50km inland. Where the sea is calmer, this corrosivity area extends from 100k to 6km inland. Adelaide is a good example of such an area. Calm conditions such as those at Port Philip bay experience this level of corrosivity from 50m to 1km from the shoreline.

C2: Arid / urban inland – You don’t get less corrosive outdoor conditions than this. In most of Australia, this area begins about 50km from the shore, but for areas such as Adelaide, 6km inland is far enough away for these conditions to prevail. And if the sea is calm and sheltered, 1km is far enough.

How long will my galvanised steel columns last?

As we have seen, that depends on your proximity to the sea, and the conditions experienced along the sea coast, but it also depends on the thickness of the galvanising as well as the thickness of the steel. The closer you are to the sea, the thicker the steel and the galvanising you need if you want your building to last.

In extremely harsh, CX conditions, you’ll get 5 to 15 years if you use the very best materials. You get double that if you site your building in a C4 area, so if your coastline is ‘CX’, and you site your buildings from 200m to 1km from the shoreline, you’ll double their lifespan. But in arid inland conditions, the same steel gives you anything up to 100 years and not much less lifespan even if you use the thinnest galvanising.

Does paint help?

Paint certainly does extend the lifespan of galvanised columns. On its own, paint isn’t as good as galvanising, but if you cover the galvanised iron with paint and ensure that the paint coating remains intact, your structure is going to last a whole lot longer. The same applies to your farm implements. AZ/NZS 2312.2 (the new standard) recommends the right paints to use if you’re hoping to stop corrosion in its tracks. Colorbond, in which the materials come with a baked-on paint coating is the most durable and low-maintenance choice. This material was designed in Australia and is now popular all over the world.

Consider your options carefully

Obviously, we like the idea of saving on the cost of building materials, but we must make informed decisions based on the expected longevity of those materials. The new standard helps us to get an idea of how long our galvanised materials will last under a range of conditions and helps your shed designer to make recommendations according to a recognised standard.

A few simple calculations will help you to determine whether the benefits of using the best materials outweigh the costs, or whether the benefits don’t really warrant the expense in your specific set of circumstances.

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