Steel Posts – Duragal vs H.D. Galv

The Duragal steel post vs the Hot Dipped Galvanised steel post battle is a long-standing grudge match between two steely contenders. Which steel post is better for your house project? Get the full blow-by-blow battle breakdown here.

The Battleground

Whether your project is a new house or an extension, if you are building a timber floor above ground, there’s a chance you’ll encounter the Duragal vs H.D. Galvanised steel stump battleground.

It’s not an easy battleground either. At stake are cost, longetivity, durability, corrosivity, availability and a whole host of other “itties” that cloud the decision process.

Steel columns under a house
Steel stumps under a house

Quite often steel stumps are open to the environment, easily seen but often ignored. The steel stump battleground is a forest of columns stretching from concrete footings to the underside of timber floor frames.

Steel column lengths can vary from less than 300mm to more than 5 metres. The columns support floors, walls roofs, belongings and families. They are the critical support structure for our buildings. That’s why it is crucial you and your construction team make the right decision.

The Villain!

The villain of the battleground is corrosion. Rust. Steel cancer. Iron oxide. FeO2.

Steel’s affinity for water and oxygen is like red wine to a musketeer. Corrosion is the downfall of shiny steel stumps and the kryptonite of steel’s super strength. How can you protect yourself and your property?

The Hero!

Fortunately there is a hero: Standing between steel and evil corrosion is steel’s shiny coat of armour: Zinc.

When applied as a molten coating onto steel, zinc becomes the hero – bonding onto the steel surface and forming an impenetrable surface that staves off steel’s weakness to water and oxygen.

But steel has a choice that it must make before the battle: It must choose from a range of armours –  It must choose an armour that is light enough to be inexpensive yet strong enough to outlast the battle.

Behold the contenders!

Weighing in at 100g of zinc coating per square meter is DuraGal, marketed and sold by OneSteel. The lightest (and cheapest) of brand4the galvanised coatings, the zinc armour is only applied to the external surface of square (SHS) and round (CHS) column sections. The internal surface of DuraGal is a painted finish measuring only 35 micrometers (that’s 35 thousandths of a millimetre) thick.

Our next contender: Weighing in at 100g of zinc per sqimagesuare metre on inside and outside faces of box and round column sections is DuraGal Plus. It’s a better option than Duragal because the inside surface has a zinc coating too but it is slightly more expensive.

Finally, our superhero: Hot Dip Galvanising. Weighing in Galvanisedat a hefty 500 grams of zinc per square metre inside and out, H.D. Galvanised steel has the heaviest, strongest coat but is also the most expensive.

The Steel Stump Battle

It’s a fierce battle. What is the best thickness of galvanising for your project?

That’s a decision for you, your structural engineer and builder to make.

The Provisos

There’s a couple of issues you should be aware of:

It is well known in the construction industry that DuraGal steel and the chemicals in concrete react and fail the thin galvanised coating on DuraGal steel prematurely.

Corrode steel column
Duragal steel in contact with the ground will corrode

If you are casting DuraGal steel into a concrete footing, ask your structural engineer to document the precaution you need to take specific to your situation.

References

We used the following websites to compile this article.

4 thoughts on “Steel Posts – Duragal vs H.D. Galv”

  1. Kane,

    I fully agree with this document. Durgal in soil, is like having a Tissue Paper for a Rain Coat.

    As a Forensic Structural Engineer, I have seen too many failures to allow Durgal to be in contact with soil. A SHS may last 5 years, and not 50 Years.

  2. What would be the effect of including a simple layer of damp proof course stocking/sock…between the durogal post and it’s stump or other such support surface? whaddya mean they don’t make’em?

  3. I had a Welding contractor weld 10mm Baseplates to my Steel House stumps and Verandah Posts.
    The Duragal is 3.5mm thick and the stumps are around 1300mm long.
    He sprayed cold Galv over the plates and the welding.

    He assures me that this will be there for 70 years.

    Does anyone have an opinion on this.?

Leave a Reply

Your email address will not be published. Required fields are marked *