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Trimming Metal Roof Back With No Rusting

 
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Old 11-30-2016, 05:12 AM   #1
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Trimming Metal Roof Back With No Rusting


What's the most efficient way/tool for trimming back a metal roof without making the edge rust? Someone told me the best way was just by hand with some basic strait metal cutters...
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Old 11-30-2016, 07:28 AM   #2
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Re: Trimming Metal Roof Back With No Rusting


Any unpainted/exposed metal will rust regardless of how it's cut.

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Old 11-30-2016, 08:18 AM   #3
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Re: Trimming Metal Roof Back With No Rusting


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Any unpainted/exposed metal will rust regardless of how it's cut.
Not entirely true. Cutting with a shear or snips will seal the edge with the galvanized coating of the metal. Where as cutting with a saw tears the metal leaving it prone to rusting.
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Old 11-30-2016, 08:38 AM   #4
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Re: Trimming Metal Roof Back With No Rusting


So could I buy a good electric shear and be fine? I've got a pretty good bit if metal to cut. Almost 3 entire homes. Or even a good nibbler?

Last edited by MSgutter; 11-30-2016 at 08:45 AM.
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Old 11-30-2016, 09:04 AM   #5
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Re: Trimming Metal Roof Back With No Rusting


You should be ok with shears or nibblers, although the profile of the panel will dictate which will work better.
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Old 11-30-2016, 09:29 AM   #6
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Re: Trimming Metal Roof Back With No Rusting


This sounds like a disaster for trying to prevent rust.
There is no way it is sealing squat. Galvanizing material doesn't move. A clean edge (or polished edge) will have less surface area to rust, and the existing galvanizing material on the metal will prevent the rust creep.

A sheer or nibbler will be cleaner, and not have hot metal sparks that can in-bead into surrounding surfaces which will rust and appear to be as if its the base metal. Thats the reason to choose a sheer or nibbler/cutter,etc.,

If you want to restore some protection to the edge, after cutting, wipe down with denatured alcohol, then apply a cold galvanizing compound. Easiest applied with a roller just on the edge, then top coat the edge with a roller with matching paint, or clear coat.

If you dont, the existing zinc will eventually be used up close to the edge, and rust will start spreading.
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Old 11-30-2016, 09:48 AM   #7
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Re: Trimming Metal Roof Back With No Rusting


The profile will be similar to this. Which would be better for this profile? Shears or nibbler?
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Old 11-30-2016, 10:00 AM   #8
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Re: Trimming Metal Roof Back With No Rusting


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Originally Posted by MSgutter View Post
The profile will be similar to this. Which would be better for this profile? Shears or nibbler?
I don't do metal as often as these other guys, but I use Malco turbo shears when cutting the Americana profile like that. Seems to work well.
It's a bit awkward, but faster than hand shears. I attach it upside down in the drill, makes it easier for me to get over the ribs
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Old 11-30-2016, 10:19 AM   #9
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Re: Trimming Metal Roof Back With No Rusting


metal cutting blade in a circular saw.
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Old 11-30-2016, 10:28 AM   #10
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Re: Trimming Metal Roof Back With No Rusting


btw dewalt is supposed to have a sheer attachment.

https://www.amazon.com/DEWALT-DWASHR...ag=toolguyd-20

supposed to cut 18 ga

The problem with that profile is that a lot of shears will deform that profile. If it were me (and Im not a roof guy) but if I had to do more than 3 feet of cutting, I'd invest in a metal cutting blade.

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Old 11-30-2016, 10:34 AM   #11
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Re: Trimming Metal Roof Back With No Rusting


Quote:
Originally Posted by Randy Bush View Post
Not entirely true. Cutting with a shear or snips will seal the edge with the galvanized coating of the metal. Where as cutting with a saw tears the metal leaving it prone to rusting.
Good point
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Old 11-30-2016, 10:41 AM   #12
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Re: Trimming Metal Roof Back With No Rusting


Those panels are common where I used to live, and I'm writing this under a 35 year old one in Alaska right now. The cut edges never seem to be an issue.
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Old 11-30-2016, 02:09 PM   #13
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Re: Trimming Metal Roof Back With No Rusting


Quote:
Originally Posted by madmax718 View Post
This sounds like a disaster for trying to prevent rust.
There is no way it is sealing squat. Galvanizing material doesn't move. A clean edge (or polished edge) will have less surface area to rust, and the existing galvanizing material on the metal will prevent the rust creep.

A sheer or nibbler will be cleaner, and not have hot metal sparks that can in-bead into surrounding surfaces which will rust and appear to be as if its the base metal. Thats the reason to choose a sheer or nibbler/cutter,etc.,

If you want to restore some protection to the edge, after cutting, wipe down with denatured alcohol, then apply a cold galvanizing compound. Easiest applied with a roller just on the edge, then top coat the edge with a roller with matching paint, or clear coat.

If you dont, the existing zinc will eventually be used up close to the edge, and rust will start spreading.
All factory cut are done with a shear / guillotine. that do not have any extra treatment done to the cut edge and do not rust. Cutting with a shear or even snips sacrifices or rolls the edge as it is cut there by sealing that edge.

Where as with a blade you are tearing the edge as you cut leaving a very raw edge that is prone to rust. In over 20 years I have never used a blade to cut my roofing or steel siding. Most of my steel siding says right on the box "Do not cut with saw"
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Old 11-30-2016, 02:14 PM   #14
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Re: Trimming Metal Roof Back With No Rusting


I ended up buying a malco shear that connect onto a drill.
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Old 11-30-2016, 02:34 PM   #15
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Re: Trimming Metal Roof Back With No Rusting


Quote:
Originally Posted by Randy Bush View Post
All factory cut are done with a shear / guillotine. that do not have any extra treatment done to the cut edge and do not rust. Cutting with a shear or even snips sacrifices or rolls the edge as it is cut there by sealing that edge.

Where as with a blade you are tearing the edge as you cut leaving a very raw edge that is prone to rust. In over 20 years I have never used a blade to cut my roofing or steel siding. Most of my steel siding says right on the box "Do not cut with saw"
Id understand that more with the large guillotine types, as it literally squeezes the two pieces apart- but Im not certain that happens with snips. Either way, if thats what the box says, and you have 20 years in doing it, I'll take your word for it.

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