Will drilled galvanized steel rust?

Letter 24491

Will drilled galvanized steel rust?

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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

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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) [link is 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, P.E.
finishing.com
Brick, New Jersey

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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
- White Rock, B.C. Canada

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