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topic 24491

Will drilled galvanized steel rust?



A discussion started in 2003 & continuing through 2017 -- add your Q to bring it back to the Hot Topics page.

(2003)

Q. I am a member of a horse riding club. We are currently working on a volunteer project. We are installing new gates and fencing to our community arena. Some of the gates require a hole to be drilled and a galvanized bolt to be inserted, a galvanized nut tightened on the opposite end. This is also how we have hung informational signs on some of the gates. One member of the committee insists that holes cannot be drilled into galvanized steel, even if the hole is immediately fitted with a galvanized nut & bolt combination because it will remove the galvanization and cause rust. Some of these holes were drilled and a nut & bolt installed 3 years ago and there is no sign of rust. Is rusting a legitimate concern? Should silicone caulking be applied?

Georgette Pierson
hobbyist - Bend, Oregon


(2003)

A. The beauty of galvanized steel compared to painted steel is that it offers galvanic protection. That is, the zinc coating dissolves preferentially to the steel rusting, to protect it despite scratches and cuts in the coating. It is not impossible for the uncoated area to rust, but basically galvanized coatings are ideal for exactly what you are doing. It would do no harm to paint the raw edge of the steel, and if you used a zinc-rich paint (cold galvanizing) [linked by editor to product info] that would be best, but I think you are unlikely to see any rust stains seeping out over the long term even without it.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2003)

A. Hi Georgette,

Yes, Ted is right.

But IF you are still worried, then why not liberally coat the thread with a suitable oil, something like Molyslip, or if you really want to gild the lily, first of all use Teflon tape and then that oil ... and touch up with some zinc rich (silver) paint on the outside, like Ted suggested. But I wouldn't want to use a lock washer, which you might have to, as that could cut into the coating. Way out? Sure! Use a flat washer and THEN the lock washer.

freeman newton portrait
Freeman Newton
White Rock, British Columbia, Canada

(It is our sad duty to
advise that Freeman passed away
April 21, 2012. R.I.P. old friend).



August 12, 2010

Q. Hello,

I noticed this quick thread and wanted to ask another question based on the galvanized steel information. I have to cover the styrofoam on the base on my new home (the styrofoam cover the cement foundation) and I have chosen 7/8 corrugated metal - galvanized. I was not going to use a drip edge at the bottom, but rather, have the galvanized sheets go into the ground (crushed rock) for the most part and then use a drip-edge around the entry-points where there is a cement slab.

The company that I have purchased this from has stated that it will not be a problem and because the sheets won't be in standing water, they should not rust for a long period of time. Any thoughts or further comments would be greatly appreciated!

Dennis Marchiori
- Yellowknife, NT, Canada


August 15, 2010

Q. Hello, just as a follow up to my question above, the material is 26 gauge sheets of corrugated metal (Vicwest is the maker of it here in Canada)and I am running it vertically on the base of my house. The most that the metal will be into the ground is about 2 or 3 inches...

I guess my question is whether or not I should use the drip-edge on the entire perimeter of the house and if that will provide a much longer life-span for my metal sheets?

Not sure that this additional information is required, but thought I should provide as much information as possible.

Again, thanks in advance for any information or insight on my question!

Dennis Marchiori [returning]
- Yellowknife, NT, Canada


A. Hi. I disagree with that, Dennis. Although the galvanized zinc coating is supposed to protect the steel, the zinc itself is a very active metal -- if you put zinc into a mild acid, for example, it will corrode much faster than steel will.

For the zinc itself to not corrode it should be exposed to open air so that, over the course of months or years, a tight zinc carbonate glaze forms on it which is rather impervious to corrosion. It's not that galvanizing can't be put into the ground, it's that it won't work nearly as well.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Protecting edges of galvanized cable trays

August 12, 2017

Q. Hi Georgette
I'm working in a project installing hot dipped galvanizing and the client isn't satisfied with zinc spraying the cut edges.
They are asking for a stainless steel or aluminium tray.
What product is out there that can seal cut edges with as great or better sealing as the galvanizing
Thank you for any help
Alain

Alain Rozic
Electrical industry - Melbourne, Australia


August 2017

A. Hi Alain. Georgette's question was from 14 years ago, so it's unlikely she'll see your response.

Heavy hot dip galvanizing is the most corrosion resistant finish there is in some applications, with unmaintained galvanized structures 75 years old and more out there, so nothing can seal the edges as well. But maybe it doesn't have to because the galvanizing offers reasonable sacrificial protection to the cut edges anyway. A good solution might be to roll the edges so there are no uncoated exposed edges; and a better one might be to galvanize after fabrication. Still, stainless may be a better overall answer. Good luck.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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