# Forum Home Renovation Roofing  Gal v Zinc

## Bluegum

I need to replace some of the guttering as the old stuff has just about run its race.  Zinc is cheaper than gal, however I have a gal roof.  Now I have been told that I cant use zinc because of this as the run off from the gal will cause it to break down through electrosis of some form.  Yet if I was to have a zinc roof then gal gutters dont mattter as the electrosis is not as bad.  This was from a local steel merchant so I'm a bit confused so I figured that some one in here could explain to me what they're talking about.  He also gave me a quote to replace the roof with zinc at about $60 per metre.  My roof will eventually need some work as its 50 odd years old so as for his quote is this a reasonable price?

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## DavidG

Quote from 
Our very own Macquarie Dictionary defines galvanised iron as iron coated with zinc to prevent rust and such iron formed into corrugated sheets and used for roofing etc, esp. in rural buildings and outhouses.  
This definition only describes accurately the now rare zinc coated wrought iron of the nineteenth century, which was replaced by mild steel from the 1890s. The gal iron that became such an important part of the Australian vernacular is in fact galvanised corrugated steel.  
Today, however, the most popular and best-promoted corrugated roofing is Zincalume® or the factory coated version of Zincalume®, Colorbond®. These materials look and behave quite differently from traditional galvanised sheet. Galvanised sheet is still available today but is a rather different product from the hot dipped sheet produced up to the 1960s. These changes have created a dilemma for heritage professionals advising on galvanised roofing repair and replacement and on new corrugated roofing in heritage areas.  
Zincalume® (55% aluminium, 43% zinc and 1.6% silicon) is superficially similar in appearance to galvanised sheet but retains its bright shiny appearance for much longer. It cannot be used in conjunction with galvanised gutters and downpipes, which must also be replaced if a galvanised roof is replaced with Zincalume®. It is also not compatible with lead flashing, which makes for difficulties in retaining or reconstructing original details.

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## Batpig

Dear Bluegum, 
I'm fairly sure that it might actually be the other way around - ie. Galvanised Roof flowing into Zincalume Gutters is AOK, as in  :2thumbsup: ...
From what I understand, you'll only get the problem you fear when you have a Zincalume Roof flowing into Galvanised Gutters...
Hope this saves you some Folding Stuff... 
Best Wishes,
Batpig.

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## David L

IMHO if you have a gal roof use gal gutter.
I wish I had done that a few years ago then no problems.
I had a gutter rust out in just a few years.

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## Qldp

Gal roof and zinc or colourbond gutters are fine. Zinc or cb roof and gal gutters are fine for a few years then it will be, a case of replacing your gutters with new zinc or cb. 
$60 a sq m for a re-roof is ok. It depends on the roof(amount of hips,valleys  etc).
As always get a couple of quotes. Consider insulation if you haven,t got it.

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## Bluegum

Thanks for that as I said I didn't really know where to start.  Our roof is straight forward gable with no hips or valleys so the job shouldn't really entail to much detail.  The roof itself is just starting to age a bit as I had to bog up a hole in the tin last week.  Its when I started to look at the actual idea that I may have to replace it.  I would be insulating as well as currently there is none.

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## Barry_White

> I need to replace some of the guttering as the old stuff has just about run its race.  Zinc is cheaper than gal, however I have a gal roof.  Now I have been told that I cant use zinc because of this as the run off from the gal will cause it to break down through electrosis of some form.  Yet if I was to have a zinc roof then gal gutters dont mattter as the electrosis is not as bad.  This was from a local steel merchant so I'm a bit confused so I figured that some one in here could explain to me what they're talking about.  He also gave me a quote to replace the roof with zinc at about $60 per metre.  My roof will eventually need some work as its 50 odd years old so as for his quote is this a reasonable price?

  Bluegum 
I answered this in another thread. 
And BTW Gal is actually Zinc and the correct word for the other is Zincalume but have a look at my other post.  http://www.woodworkforums.com/showpo...4&postcount=19

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## Bluegum

Thanks for that Barry I really appreciate it.  At least I have more of an understanding in regards to my original question.

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## Don777

Gal and Zinc roof together basicilly OK
Dad was Metalurgist and did garage with sloping roof top section was old gal,  bottom section new zinc ( 2km from port phillip bay ) did was this about 25 years ago ( no problems yet )
Also on the strength of Dad's comments the roof on the factory where I work is Gal sheet with Zinc box gutters done about 15 years ago and no problems 
So the way I look at it is whatever is cheaper 
Cheers Don

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## silentC

> Gal and Zinc roof together basicilly OK

  Run off from Gal onto Zincalume is OK. Run off from Zincalume onto Gal is not. That's point and the gist of what Bazza posted in the other thread.

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