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TOPIC: Galvalume

Galvalume Steel Tile: Nailed and Cut - Will it Rust?

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I had a steel roof installed two years ago with Gerard tiles. This is a Galvalume product. I understand how the galvanizing process protects the underlying metal from rusting, however, I know that to install the tile, it is both nailed through and cut. Doing this would seem to breach the protective coating and expose the metal to rusting over time. I've asked Gerard about this via email more than once, but they never answer. No one else so far has had a convincing answer to put my concerns to rest. Do we have a problem here?
Guest User

11/11/2007
When you do any sort of shearing action down through the steel, you obtain a certain anount of "wipe" of the zinc / aluminum coating on the steel which provides cut edge protection. This does a good job of helping avoid corrosion on those critical points. In highly corrosive environments (such as salt air environments) the actual cut edges would be protected during the installation process by a rust inhibiting paint. Todd Miller
Todd Miller
Isaiah Industries, Inc.

11/14/2007
Salt spray is a real concern for a lot of building materials. I don't think anyone likes talking about it. You can research how zinc is self healing. Your roof's life will be based on the Galvalume's ability to heal itself. Here's a technical bulletin for starters: http://www.dofasco.ca/bins/doc.asp?rdc_id=518
Brian Selig
Architectural Building Components Metal Roof and Wall Panels

11/14/2007
Thanks Brian. Todd Miller
Todd Miller
Isaiah Industries, Inc.

11/16/2007
The zinc coating does not "wipe". The exposed steel is protected from red rusting by "galvanic reaction". The zinc is preferentially oxidized (forming white rust), but the steel is unoxidized. When all the zinc in the galv coating (near the cut edge or nail hole) is consumed in this reaction, the steel will begin to rust.
Guest User

1/16/2008
Thanks. Todd Miller
Todd Miller
Isaiah Industries, Inc.

1/29/2008
Sorry Larry, but you're comment about the zinc turning to "white rust" and eventually disappearing completely from a cut edge or hole just isn't right with zinc-aluminum alloy steel coatings, which was the protective coating in question. In the past all we ever used was zinc by itslef to coat steel. And as the zinc naturally oxided and turned to white rust it eventually disappeared, leaving the steel exposed to the elements to rust away. Today, aluminum has been specifically added to zinc to "stabilize" it and prevent the oxided "white rust" of old. The new zinc-aluminum coating for steel is designed to protect it for decades, whether cut, nailed, or both. And as correctly stated in another post, it does this by creating a "wipe" or "smear" with the Zn-Al alloy mix to "coat" the edge of nail-holes and edge-cuts as their made.
Guest User

1/31/2008
Thanks. Todd Miller
Todd Miller
Isaiah Industries, Inc.

2/3/2008
So is the Galvalume recommended over the painted version or not?
Guest User

5/15/2008
Galvalume is available painted or with an acrylic clear coat. On the painted side, there are various grades of paint finishes. Quality and cost tend to go hand in hand. Todd Miller
Todd Miller
Isaiah Industries, Inc.

5/20/2008