The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Artist's questions on Brushing Galvanized Metal

June 19, 2008

Hello,

I am an artist that works occasionally in metal. I like to reuse metal for practical applications as well as aesthetic applications and I recently came upon some large galvanized heating duct sections that I think would look great (with a little work) as outside planters. Since the ducting has been sitting outside for probably a number of years it is a little mottled with white rust/discoloration, etc. I wanted to spruce it up so that it had the "brushed look" that you see with a lot of stainless and other metals now. I have used a little bit of 220 sandpaper as a test and for a kind of modern lineal effect it looks pretty good.

I have 2 questions though-

1. What are the safety concerns that I should be paying attention to sanding galvanized metal? I have done a bit of research on your forums and elsewhere - and I haven't come across any posts that deal with brushed galvanized safety. There was one moderator who mentioned in a post about zinc countertops that galvanized sheet was often chromium conversion coated which made me a little leery of starting in on sanding without asking you folks first about how to do this safely. I am interested in knowing what I should be doing during the process of sanding and also whether the metal once sanded has any health hazards given that that the zinc coating might be gone and chromium exposed (i.e., will the metal break down further overtime shedding chemicals into our garden area?).

2. I have read that most brushed galvanized looks are actually done by a special finishing process and that the surface still has the protection offered by zinc. In my case I would be sanding off some of the non ferrous zinc and possibly exposing the steel. Is there any gauge by which I might know how much sanding I could do before getting to the steel layer (and then later seeing rust)?

Thank you for reading and I welcome any input.

W

Will Weeden
Artist - Seattle, Washington

---

June 19, 2008

Hi, Will. You should wear a mask / respirator when sanding anything, whether it's metal, wood, or paint. After that the additional danger of sanding galvanized is minimal. Yes, there might have been a small amount of chromate on it, but the presence of white rust means there wasn't enough to stop the white rust.

If there were any negligible amount of chrome in the dust or runoff, I doubt that it would hurt your garden. There's far more chrome on your brake housings. I've been to properties which drums of concentrated chrome ran onto for decades and they are growing fine. (I'm not saying large amounts of chrome aren't bad for the environment!)

The reason for using galvanizing is that it cathodically protects the steel even if scratched, so I don't think you're going to have major problems from an accidental oversanding of a small area.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey