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Old 03-03-2015, 02:21 AM   #1
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Default How you prep Gavaneal Metal tp paint

We've had a paint failure problem. The finish has fisheyes all Over the place. Was told the surface was steel, now after doing some due diligence, I found out its Gavaneal steel. Now we hack to strip down the paint to the bare surface then prep before we repaint.


What would be the best method to stripping down the paint then prepping the surface to get rid of contaminate?
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Old 03-03-2015, 09:03 AM   #2
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The old school way to prep galvanized is to wash it with vinegar. This etches it and removes the release agent from the surface. That'll work if its regular galvanized.
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Old 03-03-2015, 09:32 AM   #3
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Prep the way jmayspaint said then find an acrylic primer that is specific for galvanized metal. If vinegar does not clean the surface you may need to use lacquer thinner.
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Old 03-03-2015, 10:32 AM   #4
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Originally Posted by SuperiorPainter View Post
We've had a paint failure problem. The finish has fisheyes all Over the place. Was told the surface was steel, now after doing some due diligence, I found out its Gavaneal steel. Now we hack to strip down the paint to the bare surface then prep before we repaint.


What would be the best method to stripping down the paint then prepping the surface to get rid of contaminate?
Galvaneal steel is supposed to be readily paintable, unlike regular galvanized steel...I don't trust it though. I agree with both Jmays and Lambrecht that you oughta treat it like galvanized (clean with lacquer thinner, etch with vinegar or phosphoric acid)...If your issue is fisheyes, that is usually the issue of a low-tension substance (like passivator oils) on the surface at time of application. A solvent wash will take care of that - I would still etch after solvent cleaning though.

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Old 03-03-2015, 11:20 AM   #5
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I too thought he'd made a typo. I don't know if this helps but it sounds like galvaneal steel should be easier to paint than galvanized metal. http://www.steelmillsoftheworld.com/...er/G_Note5.pdf
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Old 03-03-2015, 02:07 PM   #6
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Since this seems like a relevant place to ask...does anyone know if downstreaming Oxalic Acid would be strong enough to etch galvanized sheet metal?
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Old 03-03-2015, 04:53 PM   #7
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Originally Posted by Hines Painting View Post
Since this seems like a relevant place to ask...does anyone know if downstreaming Oxalic Acid would be strong enough to etch galvanized sheet metal?
There would be nothing wrong with using oxalic acid to prep galvanize metal before painting, although there are others that may work better. Oxalic is considerably stronger than acetic acid (vinegar) is - and though not as strong as muriatic acid, it behaves in a similar fashion. Both oxalic and muriatic cleans - and etches - metal great, but quickly "rusts" the surface they have just "cleaned" (and, yes, that is an issue for galvanized as well as ferrous metals).

Personally, I prefer phosphoric acid to clean & etch metals. It's not as harsh, equally effective and leaves a layer of iron phosphate to the surface that staves off flash rusting (for awhile at least).
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Old 03-03-2015, 05:55 PM   #8
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...If your issue is fisheyes, that is usually the issue of a low-tension substance (like passivator oils) on the surface at time of application. A solvent wash will take care of that.....

Could you go into a little more detail on the passivator oils? How is that related to regular passivated galvanized? I was under the impression that passivated galvanized required media blasting or high pressure water jetting to be successfully coated. The difference between galvanized and passivated galvanized being that the latter doesn't react to copper sulfate.

Are there some forms of passivation that last longer, or are more easily removed, than others?
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Old 03-03-2015, 10:49 PM   #9
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Yea we thought the surface was readily paintable as well then came the fisheyes like a week later. I was thinking about using lacquer thinner but the surface is 20' high and 40' wide. Plus there are shrubs and plants around now.
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Galvaneal steel is supposed to be readily paintable, unlike regular galvanized steel...I don't trust it though. I agree with both Jmays and Lambrecht that you oughta treat it like galvanized (clean with lacquer thinner, etch with vinegar or phosphoric acid)...If your issue is fisheyes, that is usually the issue of a low-tension substance (like passivator oils) on the surface at time of application. A solvent wash will take care of that - I would still etch after solvent cleaning though.
I know the old paint has to come off because it has failed, but sort of methods have you guys had success with blasting paint off of steel? There is no way i am going to have our crew out there with heat guns or chemical strippers. The city is looking for contaminants after the problem is solve?
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Old 03-04-2015, 12:41 AM   #10
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Quote:
Originally Posted by Ric View Post
There would be nothing wrong with using oxalic acid to prep galvanize metal before painting, although there are others that may work better. Oxalic is considerably stronger than acetic acid (vinegar) is - and though not as strong as muriatic acid, it behaves in a similar fashion. Both oxalic and muriatic cleans - and etches - metal great, but quickly "rusts" the surface they have just "cleaned" (and, yes, that is an issue for galvanized as well as ferrous metals).

Personally, I prefer phosphoric acid to clean & etch metals. It's not as harsh, equally effective and leaves a layer of iron phosphate to the surface that staves off flash rusting (for awhile at least).

How quickly does it rust the surface? If it was painted within a week do you think it would be ok?
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Old 03-04-2015, 09:51 AM   #11
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Quote:
Originally Posted by Jmayspaint View Post
Could you go into a little more detail on the passivator oils? How is that related to regular passivated galvanized? I was under the impression that passivated galvanized required media blasting or high pressure water jetting to be successfully coated. The difference between galvanized and passivated galvanized being that the latter doesn't react to copper sulfate.

Are there some forms of passivation that last longer, or are more easily removed, than others?
Hiya Jmays...

When speaking of actual "passivated" metals (such as stainless steel, et al), that is a whole foreign sounding chemistry that I claim no epxertise in... My reference to passivator oils are the form release oils, that act as a barrier to oxygen molecules responsible for the oxidation of both ferrous and non-ferrous metals. Obviously, these oils must be removed prior to priming or painting - thus the need for a solvent wash. Just as any surface oxidation (white or rust) needs to be removed (by proper means) prior to priming or painting...and just as the zinc surface needs to be etched and neutralized by acid wash, prior to priming or painting.

Sorry, I probably shouldn't have used the term "passivator" oils...
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Old 03-04-2015, 09:58 AM   #12
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How quickly does it rust the surface? If it was painted within a week do you think it would be ok?
As much as anything, that really depends on the exposure once the surface has been etched. Using muriatic acid as the extreme, oxidation may begin as soon as a few hours following an acid wash...Oxalic acid may not be as quick to rust a surface, but given the right environment (temps and humidity), I think the surface could "flash" rust sooner than a couple of days. Your best bet will be to coat the surface as soon as the surface is rinsed and dried to avoid flash rusting.

I'm sure you already know this, but oxidation on zinc (white rust) is different than on ferrous metals, but may equally inhibit the adhesion of a primer or paint to a galvanized surface.
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Old 03-04-2015, 02:29 PM   #13
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Also, has anyone tried using emulsa bond mixed in their paint for galvanized metal for a better bond?
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Old 03-04-2015, 03:21 PM   #14
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Also, has anyone tried using emulsa bond mixed in their paint for galvanized metal for a better bond?
I wouldn't...Emulsa Bond works by giving latex paints oil based characteristics (better penetration, ability to bind in chalky, dusty residue) - the reason it provides oil/alkyd characteristics is 'cause it contains oil/alkyd resins. You could experience the same adhesion issues (saponification) with an EB treated acrylic as you could with a straight alkyd coating.
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Old 03-06-2015, 01:56 AM   #15
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Thanks for your in depth replies everyone, but does anyone recommend a way to safely strip the failing coats of paint off of galvaneal?
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Old 03-16-2015, 08:15 PM   #16
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None of you guys ever use ammonia?

Over here thats what is always used on zincked metal. Dilute with water, mix it with a bit of dishsoap, scrub it in with a sanding sponge, let sit 10min then rinse with water. Also good for hard PVC plastics.
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Old 03-16-2015, 08:17 PM   #17
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What kind of paint? If its oil based/ alkyde resin based you can also remove it with ammonia in stronger concentration, thickened with wallpaper paste.

Dont think oil/alkyd works with zink (galvanization) at all though
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Old 04-02-2015, 08:50 PM   #18
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Never oil over galvanized. You can right over galvanized if its prepped and cleaned correctly with an industrial product, many have flash rust resistance. However, I'd recommend Procryl primer if there is any rusting involved.
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Old 04-02-2015, 09:02 PM   #19
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None of you guys ever use ammonia?

Over here thats what is always used on zincked metal. Dilute with water, mix it with a bit of dishsoap, scrub it in with a sanding sponge, let sit 10min then rinse with water. Also good for hard PVC plastics.
I assume the ammonia/detergent/water is to remove oil contamination on the surface. We learned to degrease new galvanized with solvent, typically Varnish Makers' and Painters'.
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Old 04-03-2015, 03:42 AM   #20
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Yes, but I think its alkalinity (or maybe simply corrosivity) also plays a important part as well.
Its important to mix it right, though. Its meant to lightly abrade the zinc, but if you make it to strong youll start to break down the zinc coating.

Heres how its usually mixed:

10L water
0.5L Ammonia in 25% strength
A few squirts of soap.

If you use weaker Ammonia, you have to adjust the recipe.
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