Laying Out Barn Metal

[jaw22w]

I'm currently trimming a new lean-to on the barn with metal siding and trim. I discussed it with a friend who has years of experience leading a crew of ironworkers in constructing metal buildings. He's quite knowledgeable. He advised against laying out sheets or trim with a pencil, claiming it causes rust. This was new to me, and I'm hesitant to doubt him.

Has anyone heard of this? Is there any truth to it?

 

[The Cobbler]

from the web
Graphite is more noble than all metals, therefore any metal in contact with graphite becomes an anode, or a negatively charged surface, and starts to corrode.

not sure how or if that would affect painted surfaces

 

[jaw22w]

from the web
Graphite is more noble than all metals, therefore any metal in contact with graphite becomes an anode, or a negatively charged surface, and starts to corrode.

not sure how or if that would affect painted surfaces

Yep! I didn't think of that. The whole dissimilar metals thing. I guess I didn't think of it because of the paint. I would think that would stop the electrical flow. But then some of the graphite could become embedded during the cutting process, shearing or abrasive, I guess. Looks like my buddy might be right. His family ran a small foundry when he was younger, so he knows his metals.

 

[jaw22w]

I like laying out with pencil much better than using a sharpie. Gives a much sharper, more precise line for cutting. So, here's what I'm going to do. Lay it out so that I am always cutting off the pencil marks! Just for my buddy, Leebo.

 

[PCustoms]

Its going to rust (eventually) because you cut the edge exposing raw steel, not because you used a graphite pencil to mark the cut line.