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zinc vs stainless vs galvanized vs aluminum hardware.

8-ball

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Just a quick question that I can't seem to find an answer to. I am doing a small roof mounted system on my RV. I am using Unistrut to mount to an existing frame that is adhered to the roof. I don't want to drill anymore holes in the roof. The Unistrut is Galvanized steel (I think), when finding hardware to use most of what I find in the store is Zinc but it says right above the zinc hardware "indoor use". I assume this is because it will rust? So I started looking for stainless steel that's when I noticed the price. One SS bolt was $3.76 and one zinc of same size was $0.47. I can't easily find aluminum that works with unistrut it all seems to fit Iron ridge or some other very expensive rail system. so my next question is should I look for galvanized? Is there any issue with using any of these types of hardware or even unistrut? I have spring nuts which are galvanized but I need the actual bolts to fit into the nut and they are not available at my local hardware store in anything other than Zinc or SS. Do I bite the bullet and go with SS or is there something else I should be using. I was planning on using antigaling lubricant as well.
 
I would look at online sources.

I use https://belmetric.com for metric fasteners. Here's an M8, 20mm zinc vs. M8, 20mm SS:

View attachment 107031

Yeah, almost 2X as much, but not 8X.

I'm sure you can find an online source.

Wow that is a much better price. I am mostly concerned with future applications as I am doing a large ground mount soon using unistrut so finding a better online source is a great resource.

But also is my thinking correct that zinc would rust?
 
Mixed results with Zinc fasteners. If they are simply outside, but protected from direct sunlight and rain, by the array, I would expect them to be fine; however, for any fasteners directly exposed, I would prefer stainless.

I ordered stainless for the hardware I used to assemble my array mounting hardware.
 
Mixed results with Zinc fasteners. If they are simply outside, but protected from direct sunlight and rain, by the array, I would expect them to be fine; however, for any fasteners directly exposed, I would prefer stainless.

I ordered stainless for the hardware I used to assemble my array mounting hardware.
Awesome thank you.
 
Agree with waffleman. Online if often a much better deal than home despot for stainless. Ebay and amazon. Esp if you buy 10 or more at at time.
 
I buy my stainless hardware in a bulk box from Hamilton Marine in Maine. They have a minimum 10% off sale in the spring and fall. I also use never seeze on all SS threads as SS fasteners have a tendency to gall.
 
Most hardware store zinc fasteners are shiny electroplated zinc which doesn't resist outdoor corrosion very long as it's a very thin coating. Other hardware store fasteners are shiny cadmium plated which also gives minimal protection.

Lumber stores often sell hot-dipped galvanized bolts (rough grey finish) which are very durable and fairly compatible electrolytically with aluminum rails.

Stainless fasteners also have a range of corrosion protection ranging from the minimally rust resistant type 18-8 stainless, through 306 and 316 stainless types which are pretty good in exposed environments. However stainless will corrode aluminum if in contact unless teflon paste (teflon plumbers paste or Tefgel from marine stores) or nylon washers are used to isolate these two dis-similar metals. You have to be careful to not use copper based Never-Seize on anything in contact with aluminum as that will accelerate electrolytic corrosion. There is a non-copper based version.
 
unitstrut is electro plated as well :/
Any installers go back on old installations with unistrut and notice galvanic issues with the electroplated galvanized hardware used to install them?
I think I should just grab some extra nylon washers to throw between any metal and the frames at mounting surfaces since I am using unistrut as well.
 
My 20 year old installation has aluminum panel rails on Unistrut (the gold electroplated variety versus the dipped) and I see some staining and loss of zinc on the strut that is in direct contact. I used stainless fasteners between the panels and racking. On my newer pole mount I bought a sheet of UHMW plastic and cut C shaped washers that slip between the panel and the frame. On that 14 year old array I see no corrosion between the panels and the strut. Note I am up in the mountains well away from the coast so salt air is not an issue and its set back from the road so deicing salt is not an issue.
 
I bought a sheet of UHMW plastic and cut C shaped washers
what thickness and did you use something like a hole puncher to make these? I imagine you could use a hole saw, push them out every 5 or so, then take that to a jig on a bandsaw or belt sander to do it "quickly"

I think I need to get some UHMW for some of my buss bars in the future.
 
It was about 1/16" thick. I just cut it with a drywall knife. They are not really visible.
 
The thing about a nylon washer, a split washer, or another material that can degrade or fall out. It leaves you with no tension on the bolt. This is a serious condition.
 
I use nylocks on all my bolts. Yes they can loose tension but I run diagonal bracing to cut down on racking.
 
Awesome thank you.
Ahhh …my old friend Zinc rears it’s lowly head onve more…Eggman is right….SS is preferable outside..
why do you think we Fasten ZINC peices to The bronze shafts on boats…or put screw-in replaceable ZINC anodes inside the salt water heat exchanger on a sea water cooled diesel. ?

This topic is far wider in scope than what I say here but some parts of it play into solar gear exposed to water and contaminants in the Air

Because when connected to other metals and in any environment that has electricity ( galvanic or stray current) and moist or wet electrolyte environment ,the lowest metal on the “nobility table of metals “ that are connected together in that environment will get attacked and destroyed first , sparing the other metals attached.

It is more complex than this BUT, once the ZINC is eaten or wasted away the electricity will move up the the next level above Zinc on the table and attack it…, and so on and so on..eventually all the fasteners and bonded metal peices in that environment are attacked except the most noble in that group,( usually SS) and they fail , fall out or loosen or be destroyed ,then your boat can flood and not work properly or maybe sink at the dock…. Ouch.!

I’ve seen it happen. It makes the owner look very lubberly ..!

it’s why we call them sacrificial anodes. They get generally attacked first and dissolved.( not always)
Zinc is low on the table of metals ..but it’s a great mineral suppliment for Men to take …ha…( different disscusion).

SS is a much better choice for outside weather jobs .. .some grades are better than others for corrosion and strength………….
( different disscusion).

all grades are better than Zinc stuff though Hot Dipped galvanized is much better and more expensive than cold dipped gear .


Cold dipped Zinc is typically used as a cheap shield for rust and corrosion in cheaper and weaker metal pieces Hot dipped is used mainly in such high dollar anchor chain, quality marine fittings and Etc…
choose wisely if it’s a load bearing or an important piece of gear.

FWIW…J.
 
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I used aluminum unistrut 20' L and ss hdwr.

I do wish I could afford titanium hardware. I have an old timed/cycled out titanium turbine disk and hardware out of an overhauled business jet engine. It's been out in the weather for 27 years, exposed to much cooler temperatures. We've used it for a bird feeder some. Now it sits in front of my power shed.
 
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I used aluminum unistrut 20' L and ss hdwr.
Insulate the fasteners from the frame ( there is several ways..) ……otherwise you get a nice little circle of white corrosion growing around the fitting at some point… it’s called the the less Noble getting assimilated by the Nobel..or , big fish eat little fish.
Yes, that’s a Borg anolgy…
J.
 
I think I read from Unistrut catalog that zinc electroplated "pre galvanized" could hold up outdoors 5 years, vs. hot-dipped galvanized 20 years.

Some of my hardware is just welded 1/4" plain steel. It has a nice brown patina.
My ground mount array is mostly 2" galvanized conduit, galvanized or aluminum brackets, aluminum rails, stainless hardware.
Stainless hardware on clear anodized aluminum I was able to unbolt 18 years later. I think the mill finish too.
Mild San Jose environment, away from the coast, 10 miles from the Bay, not in the fog.
 
I have a ground mount array on unistrut and used the standard zinc green box hardware from Lowe’s and it’s been through one season and there’s zero rust streaks so far. Lowe’s also has hot dipped galvanized but I hate working with it.
 
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