Thread: Zincalume or Galvanised?

Thanks for the advice on the Makita saw - the shack is now progressing - I am planning to clad it in corrugated iron - roof and walls - I have been told the galvanised iron is not as shiny as zincalume - or at least it isn't when gets older - any views on which is preferable? I would prefer something not to shiny as it is a bush block.

dunno if you can still get galv. sheeting

yuo can still get Gal corro. Any of the roofing suppliers will supply. It will fade but still takes a year or two to do so. Definitely a better look in the bush, We use it fairly often on heritage work.

Galv is zinc isnt it?
Galv =electroplated in Zn?
Zincalume =hot dipped in Zn?
Anyone know?

I think you'll find that zincalume is a pretty hi-tech multi-layer process, probably involving electroplating steps, and a pretty good product for strength-for-lightness and durability (as long as all contacting metals are compatible). This compatability issue has been touched on elsewhere by those who know-(possibly on this forum-) but is important to get right.
Gal is (I think) on a heavier gauge sheet, and is a straight zinc coating- traditional and more "timeless"

Good question Harry.

I recently asked a similar question and I feel I may have gotten the wrong advise. My take on it is this -

The corrugated iron is now zincalum finished or colorbond finnished

I don't know what the old corrugated iron was ...if or not it was hot dipped zinc and I don't know if it is still available.

I know at work when we dip metal into molten zinc it looks like zincalume after its cooled down.(it did have small amounts of lead in it as well tho bout .1%)

Gal is plain zinc, I think the real old stuff mighta been hot dipped , dunno about the later stuff.

Zincalume is coated with an aluminium/zinc alloy, and is incompatible with gal sheet
(It doesn't even like galvanised roof screws)

Information from the horses mouth. Ex Lysaght Bluescope Rep/Manager.

Both Zincalume and Gal are hot dipped continuously on a machine that unrolls the flat steel coil on one end of the machine through a bath of molten zincalume or gal and the thickness of the coating is controlled by a blast of air across the surface of the steel and when it comes out of the machine it is rolled up again into a coil that can be up to 10 tonnes in weight.

This machine runs at high speed and and never stops through what is called an accelerator that allows them to join and cut the flat strip whilst the machine is continuously running.

The Colorbond is painted in a similar manner except it runs through a horizontal oven to dry the paint and the steel strip is supported on a cushion of air that runs for about 50 to 75 metres in length.

The gal coating is actually pure zinc and the zincalume is a mixture of zinc and aluminium.

Gal has a larger spangle than zincalume. As was said earlier gal will dull off to a dark grey and the zincalume will hold its shine for a very long time.

You can run water of gal onto zincalume but if you run water off zincalume onto gal the water will begin to remove the gal coating and expose the bare metal hence it will begin to corrode.

According to the bluescope steel site " ZnAl steel imparts corrosion resistance of up to four times the life of galvanised steel."

Zincalume has both the benefits of zinc and aluminium as an anti corrosion coverings. Aluminium forms a thin metal oxide coating over the steel reducing the amount of oxygen getting through to the steel underneath. The zinc acts as a sacrificial metal that grabs any oxygen preferential to the iron in the steel. Ideally one would cover the steel with Al but Al is more expensive than Zn and Al is not easy to bond to steel whereas an alloy of Zn/Al makes a good bond. Zn/Al is also more resistant to acidic rain than straight Zn.

Originally Posted by Barry_White

Information from the horses mouth. Ex Lysaght Bluescope Rep/Manager.

Both Zincalume and Gal are hot dipped continuously on a machine that unrolls the flat steel coil on one end of the machine through a bath of molten zincalume or gal and the thickness of the coating is controlled by a blast of air across the surface of the steel and when it comes out of the machine it is rolled up again into a coil that can be up to 10 tonnes in weight.

This machine runs at high speed and and never stops through what is called an accelerator that allows them to join and cut the flat strip whilst the machine is continuously running.

The Colorbond is painted in a similar manner except it runs through a horizontal oven to dry the paint and the steel strip is supported on a cushion of air that runs for about 50 to 75 metres in length.

The gal coating is actually pure zinc and the zincalume is a mixture of zinc and aluminium.

Gal has a larger spangle than zincalume. As was said earlier gal will dull off to a dark grey and the zincalume will hold its shine for a very long time.

You can run water of gal onto zincalume but if you run water off zincalume onto gal the water will begin to remove the gal coating and expose the bare metal hence it will begin to corrode.

Too true.
In my experience Gal last better lasting than Zincalume where Galvanic action is not a factor. Most notably in water tanks.

Ross

Does spangle = shine? Ok here is an even harder question... I ordered gal from my supplier - lots of pre cut sheets - it has arrived and now my supplier has rung me to tell me that he made a mistake and ordered zincalume - should I put up with it and take it? I wanted gal but I am trying to work out whether zinc will be have much more shine. So we move onto ethics!

Spangle = the odd shaped patterns that form on the surface of the coating, a bit like flakes. Gives it that motley colour. The 'flakes ' on gal are much larger than zincalume.

I'd stick with the zincalume, it's a better, longer lasting product.

gal will last longer if you are near the coast

No I am not near the coast - rather in Central Victoria - does Zincalume dull off or does it always stay shiny?

it stays shiny a lot longer than gal

That's why my roof is Dune Grey Colorbond. I wanted the look but the local airport gets a bit ancy about tin roofs.

Originally Posted by silentC

That's why my roof is Dune Grey Colorbond. I wanted the look but the local airport gets a bit ancy about tin roofs.

Can't the pilots afford sunnies?

Mick

That's the stupid thing, they all wear those dark glasses that they get free when they graduate from flying school.

But then, I don't want them crashing into my house, so I did what I was told...

I'm nowhere near an airport but we aren't allowed shiny rooves (roofs?) either. Its so people living higher than you don't get their retina's blasted.

Originally Posted by echnidna

gal will last longer if you are near the coast

Not true Bob

Originally Posted by Bleedin Thumb

I'm nowhere near an airport but we aren't allowed shiny rooves (roofs?) either. Its so people living higher than you don't get their retina's blasted.

I knew someone who had one of those A-frame houses that were popular in the 70's. The roof was tin and they were eventually forced to paint it after complaints from the neighbours who were getting blinded in the morning or afternoon (depending on which side of the house they lived).

I've just started doing re-roof (Colourbond) and wall cladding (zincalume) on our house.

We wanted galvanised sheet walls mainly because of the aesthetic value (it fades out nicely) however:

1) galvanised iron is way more expensive than zincalume
2) galvanised iron does not come with a perforation/corrosion warranty like zincalume does...

Basically it was the former that nailed it for us.

Take the zincalume....

This is for the benefit of ytbc showing the difference of gal and zincalume after about 20 years of weathering.

Is gal on the left?

Originally Posted by ytbc

Is gal on the left?

Yes

Mick

Originally Posted by ytbc

Is gal on the left?

As Mick said yes.

Originally Posted by ytbc

the shack is now progressing - I am planning to clad it in corrugated iron - roof and walls - I have been told the galvanised iron is not as shiny as zincalume - or at least it isn't when gets older - any views on which is preferable? I would prefer something not to shiny as it is a bush block.

Things you need to know:

corrugated iron is what Blue Scope Lysaght calls Custom Orb® and Custom Blue Orb®

If you're happy to go with one of the Colourbond colours or Zincalume then you can use Custom Orb® which is available with a Base Metal thickness (BMT) of 0.42 or 0.48mm

if you must have galvanised (Lysaght calls it Zincform — zinc coated galvanised steel) you'll have to go for Custom Blue Orb® which has a BMT of 0.60 or 0.80mm

the base metal thickness directly translates to cost

don't forget that you can have any length sheet you want — usually the practicle limit is the length of the truck making the delivery — eliminating the end lap between sheets saves you money.

for most people, the difference in base metal thickness translates to the spacing of the batterns to which you screw it and hence the number of screws you need.

be sure to get the battern and screw spacing right for your area


ian

Originally Posted by ian

if you must have galvanised (Lysaght calls it Zincform — zinc coated galvanised steel) you'll have to go for Custom Blue Orb® which has a BMT of 0.60 or 0.80mm

ian

Ian

As far as I know up to three and a half years ago Lysaght were still rolling 0.42 BMT Zincform Custom Orb Hi-Tensile. The Custom Blue Orb is used for curving such as Bullnose or for water tanks.

The Custom Orb in zincform 0.42 is used as normal roofing and they also keep it for roofing on intensive farming such as piggery's and poultry sheds.

Blue Orb has a tensile strength of G300 and Hi-Tensile Custom Orb steel has a tensile strength of G550.

There is also a difference of the coating classes of the two steels.
Custom Orb Z/L has a coating class of AZ150 which is 150 grams of coating to the m2
Custom Orb Gal has a coating class of Z450
Custom Blue Orb Z/L has a coating class of AZ 150 and AZ200
Custom Blue Orb Gal has a coating class of Z600

The reason the gal has a heavier coating because the life of gal is directly related to the thickness of the coating whereas with Zincalume the coating thickness has mainly no bearing on the life of the zincalume.

Barry

Through a coleague at work I've obtained a copy of Lysaght's latest Referee.

It lists Zincform as an available finish for 0.60 and 0.80 Custom Blue Orb but not for the thinner 0.42 or 0.48 Custom Orb.
But you can have stainless steel in 0.42mm Custom orb for your piggery if you want


ian

Originally Posted by ian

Barry

Through a coleague at work I've obtained a copy of Lysaght's latest Referee.

It lists Zincform as an available finish for 0.60 and 0.80 Custom Blue Orb but not for the thinner 0.42 or 0.48 Custom Orb.
But you can have stainless steel in 0.42mm Custom orb for your piggery if you want


ian

Ian

Don't believe everything you read in a Lysaght Referee. I could poke holes in several things written in a referee. A lot of the time they are just reprinted from the previous edition with the date changed.

Being an ex employee I still have a few contacts. In my previous post I said up to three and a half years as far as I know they were still supplying 0.42 Zincform. But as of 8:30am this morning they are still supplying 0.42 zincform.

As far as convincing a pig farmer to put stainless steel on a piggery roof you are lucky if you could convince him to put 2nd hand roofing on his piggery.

So ytbc just go for it if that is what you prefer. The current retail price is $10.36 + GST per lineal metre but I am sure you could get a better price than that.