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Ted Mooney, P.E. RET
Pine Beach, NJ
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Electroplated versus galvanized hardware for wooden playset
Q. We purchased a cedar playset for our children, and it came with electroplated zinc fasteners (carriage bolts and lag bolts). We plan to use this set for 10+ years, and it will be exposed to quite a bit of rain. I've read that galvanized is much better for outdoor applications, but how much of a concern is this? Should we replace all of the hardware with galvanized? Specifically, I'm wondering how quickly the zinc plated will rust, and will we still be able to tighten the joints regularly as required? Will it become a safety concern or rust to the point that the fasteners can't be removed and replaced?
Additionally, we already started assembly of a few pieces so if we decided to switch hardware from this point, is it better to just leave the electroplated lag bolts that have been installed and replace only the carriage bolts? These are essential structural pieces, and I don't want to risk the integrity of the playset by leaving them if it is a problem. However, I'm wondering if replacing the lag bolts now would do more harm than good since they are screwed into the wood.
- Knoxville, Tennessee, USA
August 14, 2012
A. Personally, I'd compromise :-)
I'd leave the lag bolts because, much as I love cedar for its rot resistance, lightness, and beauty, it doesn't hold bolt threads very well (it's just not strong enough in those little thread areas). So I would not remove and reinsert lag bolts.
But I'd replace the carriage bolts and their nuts, and be able to observe whether the galvanized components hold up better. Good luck whatever way you go.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 17, 2012
A. I would be surprised to see corrosion to the point of failure in ten years, but you will likely see some surface rust before then. Hot dip galvanized will last longer, and stainless steel fasteners will last just about forever.
My fence which is treated wood, assembled with electroplated zinc nails and screws is now 14 years old, and the fasteners are still sound, although showing some surface rust.
Jeffrey Holmes, CEF
Spartanburg, South Carolina
August 17, 2012
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A. Hi Jeffrey. Your fence is old, and probably CCA pressure treated. If you replace any slats I doubt that electroplated zinc nails will last a year. The new ACQ wood is SO aggressive that I question even drippy galvanized nails for 10-year life. Zinc plated nails were gone in my deck before a year was out. I live on a saltwater lagoon, but [it seems that] the ACQ rather than the salt bears most of the responsibility. Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey August 19, 2012 August 20, 2012 A. Ted: I'm surprised your nails failed so quickly. I know it's true
that the new arsenic and chrome free treated wood is more aggressive,
but I suspect that location and climate are even more important. If
you live in a fairly high rain and humidity area, where the wood is
essentially always wet, that's one thing. If you live where the wood
is often dry, I suspect it's quite different. Jeffrey Holmes, CEF Spartanburg, South Carolina A. Hi again. Yes, stainless may be the best way to go for small fasteners in today's ACQ pressure treated wood. I understand the need we had to get away from CCA with its chromates, but ACQ has more than twice as much copper, and has been found by wood industry tests to be more than twice as corrosive to zinc as the older CCA. Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey August 21, 2012 |
Q. Thank you for the responses. We did decide to replace the hardware with hot dip galvanized and are halfway through the assembly now. I had also emailed the playset manufacturer, and she didn't get back to me until today because she was on vacation.
Can someone please tell me if she is correct in saying that the zinc plated is actually better for natural wood products outdoors? Now I don't know what to do. We've spent $250 replacing the zinc, and she's saying we're replacing it with something inferior.
This is the text of her email:
[... The Galvanized process ... is designed specifically for chemically-treated wood ... it flakes off as the bolts/lags are tightened and causes terrible black streaks in the wood ... Zinc-plated hardware is designed for outdoor use on natural wood products.]
- Knoxville, Tennessee, USA
August 22, 2012
A. Hi, Nancy. Sorry, but we can't take her private communication to you and post it on the internet for the world to see, so I just extracted pieces and will comment on them.
Remember that she is trying to justify the less expensive path which her company took. Galvanizing and zinc plating are extremely similar except galvanized coatings are much thicker. Zinc plating is not "designed for outdoor use on natural wood", nor is galvanized "designed specifically for chemically-treated wood" as the letter asserts. That is putting the cart before the horse, and misleading: that's not why we have zinc plated hardware, nor why we have galvanized hardware. Her implication that zinc plating is not acceptable for today's pressure treated wood is also true, although per Jeffrey, it was acceptable for some earlier pressure treated wood in some circumstances.
Proper galvanizing will not "flake off as the bolts/lags are tightened" (galvanized hardware is used on multimillion dollar bridges), but I can't say confirm or deny that it will "cause terrible black streaks in the wood" or that zinc plating won't.
Galvanizing will always greatly outlast zinc plating in outdoor use regardless of environment or type of wood. Whether that longer life is overkill depends. Here in my neighborhood I'm quite sure that zinc plating will not last 10 years outdoors; in Knoxville it's different, and it might have been fine.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 22, 2012
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