top hat battens and galwanised sheeting

**Bushmiller** · 31st July 2023, 02:22 PM

Originally Posted by Bushmiller

I think much of the confusion around compatibility of galvanised iron and zincalume is to do with galvanic action and noble metals. In particular this issue is more acute when water is involved (guttering is the obvious sticking point). However, condensation forms beneath a steel roof so it can't be ignored. The foil backed building paper is probably sufficient insulation to separate the metals, but others are better qualified to advise on this.

Some links:

BlueScope Steel Australia: Avoid incompatible metals

corrosion-technical-bulletin-ctb-12-dissimilar-metals (bluescope.com.au)

BlueScope Steel Australia: Guidelines for using ZINCALUME® steel

Regards
Paul

PS: Just on a completely unrelated note, zincalume must never be in contact with the ground. This means that it is unsuitable as a rainwater tank without a suitable lining (Acqua plate etc.). Debris from the roof (dust and dirt) has the same adverse effect as being in direct contact with the ground and corrodes the tank from the inside.

**jack620** · 31st July 2023, 02:33 PM

We seem to be drifting off on a tangent. The original question was whether galvanised (zinc coated) roof sheets are compatible with zincalume (zinc and aluminium) coated battens.

I'll repost the quote I posted earlier:

"There is a misunderstanding that Zincalume is incompatible with galvanised surfaces. Zincalume is an alloy of aluminium and zinc, which are adjacent to each other on the galvanic table. They are, as can be expected, compatible in contact."

Note that is says they are compatible in contact.

**Bushmiller** · 31st July 2023, 04:37 PM

Originally Posted by jack620

We seem to be drifting off on a tangent. The original question was whether galvanised (zinc coated) roof sheets are compatible with zincalume (zinc and aluminium) coated battens.

I'll repost the quote I posted earlier:

"There is a misunderstanding that Zincalume is incompatible with galvanised surfaces. Zincalume is an alloy of aluminium and zinc, which are adjacent to each other on the galvanic table. They are, as can be expected, compatible in contact."

Note that is says they are compatible in contact.

From Bluescope steel, which is based in Australia rather than New Zealand (not that it should make any difference).

"Avoid using galvanised gutters with roofing made from ZINCALUME® steel, COLORBOND® steel or glazed tiles,"

BlueScope Steel Australia: Guidelines for using ZINCALUME® steel
Regards
Paul

**jack620** · 31st July 2023, 05:26 PM

Yep, we've established there's a compatibility issue when mixing zincalume and gal roofing/gutters. But not, I believe, between zincalume battens and gal roofing sheets.

**rwbuild** · 31st July 2023, 06:34 PM

I refer you all back to post #7

**Bushmiller** · 31st July 2023, 06:36 PM

Originally Posted by jack620

Yep, we've established there's a compatibility issue when mixing zincalume and gal roofing/gutters. But not, I believe, between zincalume battens and gal roofing sheets.

Agreed. Any risk that is there from moisture such as condensation (there is always condensation) is slight in comparison and in any event can be easily dealt with by using building paper as has already been mentioned. That is a good move anyway.

Regards
Paul

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