Author Topic: How to paint zinc-plated steel?  (Read 749 times)

zxcvbob

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How to paint zinc-plated steel?
« on: August 12, 2023, 11:39:54 AM »
I'm putting up some narrow shelves for an old widow to display her collector plates.  Going to use painted pine 1x4s from Menards (*amazingly* straight and smooth) and some 3.5" angle brackets to fasten them to the walls.  And a decorative rail across the front to keep the plates from sliding off when someone slams a door.  She had the rails already.  Everything will be painted baby blue with acrylic latex paint.  The shelves will be above eye level, and I'm going to turn the brackets with the back side facing up instead of down so it will be hidden by the shelf and the plates.

The problem is that the brackets are plated with zinc*, and I've read or heard somewhere that the paint will eventually react with the zinc (saponify?) and turn loose.  They are going on a white wall, so I want to prime them white, then paint the undersides blue to match the shelves, so the brackets mostly disappear.  This does not need to be particularly durable; it won't be subject to weathering or any wear.

Do I need to soak the brackets in vinegar or dilute hydrochloric acid to etch (possibly remove) the zinc before painting?  Or will an "etching primer" work without any pretreatment?  What about automotive primer?  I want to use just a plain old rattle-can of Rustoleum or Krylon for the primer, nothing fancy. 

*not hot dipped galvanized, this is some kind of thin bright zinc plating
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cordex

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Re: How to paint zinc-plated steel?
« Reply #1 on: August 12, 2023, 11:53:08 AM »
I would probably sand it, degrease and clean it, and then hit it with a primer designed to go over galvanized metal.

K Frame

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Re: How to paint zinc-plated steel?
« Reply #2 on: August 12, 2023, 01:10:12 PM »
You need to base coat it with an acidic etching primer first. I think you also want to match the primer to the top coat.
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zxcvbob

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Re: How to paint zinc-plated steel?
« Reply #3 on: August 12, 2023, 02:35:43 PM »
You need to base coat it with an acidic etching primer first. I think you also want to match the primer to the top coat.

I've emailed the Rustoleum company and asked if their automotive etching primer will work on zinc.  (seems like zinc and aluminum should be chemically similar), and if not what products would the recommend.  Got a generic autoreply back right away, maybe I'll get a real response early next week.

Shellac-based primer (original Kilz, etc) might work... 
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K Frame

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Re: How to paint zinc-plated steel?
« Reply #4 on: August 12, 2023, 03:19:23 PM »
"Shellac-based primer (original Kilz, etc) might work...  "

I doubt that it would last for long before it started to peel off. At least that's my gut feeling on that.

And yes, I would think that the Rustoleum stuff will work perfectly fine.
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Hawkmoon

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Re: How to paint zinc-plated steel?
« Reply #5 on: August 12, 2023, 03:32:19 PM »
Zinc chromate primer?
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230RN

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Re: How to paint zinc-plated steel?
« Reply #6 on: August 13, 2023, 07:47:50 AM »
The vinegar sounds good. You'd probably need a whole lot of it.

If it were me, I'd soak them in muriatic acid (HCl) from the hardware store until they stopped fizzing.  However, I'd be using hand, eye, and lung protection in a well ventilated area, with plenty of water handy and a couple of boxes of baking soda in case of inappropriate contact.  Disposal with plenty plenty plenty water.  HCl isn't all that bad, they use it to clean concrete and hose it down when done.

You could use sulfuric from the car parts store (used to be for replenishing the battery acid in batteries) but it's pretty expensive and I don't like the fact that even diluted, if it contacts something, the water will evaporate away and leave the con acid to etch its way around.  Usually on clothing, where mysterious holes appear some days later.  It's not the worst or strongest acid around, it's just untrustworthy.

With any acid, its strength wiil be at least partially diminished after the reactions take place.

The mist generated by the bubbles will contain the acid.

These reactions generate hydrogen gas, so no ignition sources nearby. "Well ventilated."  Hindenberg.

« Last Edit: August 13, 2023, 08:18:36 AM by 230RN »

K Frame

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Re: How to paint zinc-plated steel?
« Reply #7 on: August 13, 2023, 08:47:28 AM »
Why soak them in a vat of acid when etching primer, which contains acid to etch the surface, does the same thing with a lot less hazards?
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dogmush

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Re: How to paint zinc-plated steel?
« Reply #8 on: August 13, 2023, 09:06:32 AM »
Scuff them with a scotch bright pad, wipe clean with a good solvent, hit them with a self etching primer, and paint.  I've done this a lot with zinc plated hardware when it's going to end up painted to match.

The automotive etching primer in a rattle can works grest.

zxcvbob

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Re: How to paint zinc-plated steel?
« Reply #9 on: August 14, 2023, 04:01:30 PM »
I received a reply from Rustoleum:
Quote
Thank you for contacting Rust-Oleum Product Support.
The self etching primer can not be applied to galvanized metal.
Our recommendation would be Universal Bonding Primer that can be used on galvanized metal. Link Below:
https://www.rustoleum.com/product-catalog/consumer-brands/stops-rust/universal-bonding-primer
Nikki T.
Product Support Representative

Dogmush says he's personally used the etching primer and it worked.  Looks like I've got two choices that will probably work.  :laugh:  I know Menards has the etching primer and primer sealer.  Then it will need a top coat.  I don't know if they have the universal primer (which is white, so I might could get by with just 2 thin coats of that)  I have read that the universal bonding primer is a bitch to use.  Amazon only sells it in rather expensive 6-packs. If Menards has individual cans I may try it, otherwise I'll use the etching primer and sealer.

I haven't totally given up on the idea of soaking them in HCl or H2SO4 to remove the zinc; I have both.
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Brad Johnson

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Re: How to paint zinc-plated steel?
« Reply #10 on: August 14, 2023, 04:27:24 PM »
A vote for the Rust-Oleum suggested way. I haven't personally used the UBP but I hear it's pretty decent if you follow directions. I've used plain old etching primer on galvanized and it's okay if it's only used decoratively. If it gets any wear at all, even basic cleaning, it'll eventually begin to flake.

If you have a plating shop nearby they can zap the zinc off in just a few minutes. If you have a buddy with a sandblaster, that'll work, too. A bucket full of muriatic acid will take it off, but it's definitely an outside-only proposition which requires caution. Plus, getting rid of used muriatic is a ginormous PITA.

*edit to add* There's also the option of powder coating. Having a couple of small parts done shouldn't be terribly spendy.

Brad
« Last Edit: August 14, 2023, 04:43:23 PM by Brad Johnson »
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dogmush

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Re: How to paint zinc-plated steel?
« Reply #11 on: August 14, 2023, 04:32:11 PM »
It has been my experience that bright zinc acts more like bare smooth metal than galvanizing when dealing with paint.  Hence the scuff, etch prime, paint routine.  I've never used the Universal Primer before, but Rustoleum says it's good for anything.  [shrug]

Either way, bright zinc plated and galvanized are two very different coatings.

zxcvbob

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Re: How to paint zinc-plated steel?
« Reply #12 on: August 14, 2023, 04:53:46 PM »
Menard's has cans of the UBP, and it's cheaper than the etching primer and doesn't need a sealer.  And they have it in flat white.  I'll try that first.

I asked my pastor if he has a powdercoating rig because he's into that sort of thing.  He said no, but how'd I know it's on his list of things to get?  :rofl:
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