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Old 01-22-2020, 02:57 PM   #1
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Rustoleum Rusty Metal Primer NOT for galvanized metal

Specifically Rustoleum DTM (direct to metal) alkyd enamels. Just thought I'd throw this out there since I believe this is a popular choice w/ many folks here. A paint failure in another thread & my own research on paint for our interior roof led me to this (disclaimer against galvanized on pg. 2):


https://www.rustoleum.com/~/media/Di...llons_TDS.ashx


Always read the TDS.
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Old 01-22-2020, 03:27 PM   #2
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What happens if you do use it on Galv? Poor adhesion?
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Old 01-22-2020, 03:34 PM   #3
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I haven't used it, which excludes having a paint failure with it. But yes, I believe adhesion would be the issue. Other similar products are either designed to etch galvanized metal via direct application, or include directions on etching (like using ospho) in their TDS.
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Old 01-22-2020, 03:52 PM   #4
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I initially used Rustoleum primer on a piece of galvanized sheet I put up to cover my SCHOOL BUS sign in the back. A couple of days after it dried I was able to scrape it off with my fingernails. It also then wiped off completely just with a rag and mineral spirits - so at least it was easy to fix the problem.

I instead used Rustoleum self-etching primer and that has held up very well. SEM self-etching primer works well, too.
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Old 01-22-2020, 04:45 PM   #5
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Good to hear, Musigenesis!


Did you try the non-etching rustoleum primer after ospho / rinse? We're going w/ Behr 435 for the interior of our gutted roof, which will be under insulation (can get it local @ home depot in gallon cans). It specifies etching w/ phosphoric acid (ospho) for galvanized before application. I suspect the non-etching rustoleum might work fine w/ the same treatent, but IMO - if the TDS doesn't say anything about it, I feel better using a product that does.
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Old 01-22-2020, 05:22 PM   #6
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I used Ospho on my entire floor instead of just the rusted areas. I guess it etched all the galvanized finish off because I've got no problem with adhesion.
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Old 01-22-2020, 05:44 PM   #7
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I haven't used it, which excludes having a paint failure with it. But yes, I believe adhesion would be the issue. Other similar products are either designed to etch galvanized metal via direct application, or include directions on etching (like using ospho) in their TDS.
I've painted a ton of galvanized with it. Stuck real well in fact.
I used ospho first.
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Old 01-22-2020, 08:06 PM   #8
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I used Corroseal first, which actually dries almost like a clear coat, then applied the Rustoleum Rusty Metal Primer (even though it wasn't really rusty at that point). I think the Corroseal provided a layer between the floor and the Primer. My primer dried well, and stuck well. I walked around on it and worked on it for weeks before putting a couple of coats of Rustoleum gray paint over it. Never even scratched the primer.
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Old 01-22-2020, 08:32 PM   #9
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Based on everyone's responses it seems like the Rustoleum paint in question might have a disclaimer against galvanized either because other products of theirs fit the niche, or because they found advising people how to prep w/ ospho properly to be problematic. Reading through the Southern Polyurethanes FAQ (different paints but still relevant), they (SPI) advise against using ospho period, unless you call them for proper procedure. But in the forum they describe said process, as well as warn that not doing it properly can lead to serious adhesion problems w/ their paint. I assume similar problems would occur with many (most?) other paint types & products.

For reference:

How to neutralize Ospho | Southern Polyurethanes Forum
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Old 01-22-2020, 08:50 PM   #10
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Quote:
Originally Posted by TheHubbardBus View Post
Based on everyone's responses it seems like the Rustoleum paint in question might have a disclaimer against galvanized either because other products of theirs fit the niche, or because they found advising people how to prep w/ ospho properly to be problematic. Reading through the Southern Polyurethanes FAQ (different paints but still relevant), they (SPI) advise against using ospho period, unless you call them for proper procedure. But in the forum they describe said process, as well as warn that not doing it properly can lead to serious adhesion problems w/ their paint. I assume similar problems would occur with many (most?) other paint types & products.

For reference:

How to neutralize Ospho | Southern Polyurethanes Forum
Sure, I've seen several places (including Ospho's site) saying "Ospho n' paint"
No, no, no...
Paint's not gonna stick to Ospho residue. You need to rinse and dry the metal after ospho...
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Old 01-22-2020, 08:59 PM   #11
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Sure, I've seen several places (including Ospho's site) saying "Ospho n' paint"
No, no, no...
Paint's not gonna stick to Ospho residue. You need to rinse and dry the metal after ospho...
I just wire brush it.
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Old 01-22-2020, 09:02 PM   #12
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Ditto that, Banman.

We ospho'd our floor well, then let it sit for months as a rust preventative until the temps were favorable for painting. Followed SPI's directions to re-wet with more ospho, let it sit wet for about 1/2 an hour, then rinsed it out completely w/ a pressure washer, & dried for a day. Our paint came out perfect (performance wise).
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Old 01-23-2020, 02:41 AM   #13
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Interesting, my bottle of Ospho says that for both rusted and new metal, apply the Ospho, let dry over night, THEN APPLY PAINT.


Nothing is mentioned about re-wetting and rincing it.
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Old 01-23-2020, 07:10 AM   #14
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Interesting, my bottle of Ospho says that for both rusted and new metal, apply the Ospho, let dry over night, THEN APPLY PAINT.


Nothing is mentioned about re-wetting and rincing it.
It's in Big Phosphoric Acid's best interests for your paint not to stick - that way your metal rusts again and you need more ospho.

I've been using POR-15 sometimes which adheres really well to surfaces that I ospho and then clean with soap and water and a mineral spirit rubdown. I used it in a couple of places where I didn't clean the ospho residue first and the paint layer peeled off like a rubber sheet.
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Old 01-23-2020, 10:42 AM   #15
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Interesting, my bottle of Ospho says that for both rusted and new metal, apply the Ospho, let dry over night, THEN APPLY PAINT.


Nothing is mentioned about re-wetting and rincing it.
Exactly -- see post # 10...


I won't say that will never work but...
After Ospho, if you see a white powdery residue or a sticky residue (left on your metal) I will guarantee that no paint will adhere well to either of those conditions...
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Old 01-23-2020, 11:00 AM   #16
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Interesting, my bottle of Ospho says that for both rusted and new metal, apply the Ospho, let dry over night, THEN APPLY PAINT.

Nothing is mentioned about re-wetting and rincing it.
From the ospho website (including their typo):

"OSPHO is recommended for use under oil based primares or paints. Test trial samples before using Epoxy or other paint systems."

That potentially excludes a lot of paints (urethanes / epoxies). It also assumes they've tested it against every other oil-based paint out there, which of course they haven't.

Even where adherence on non-neutralized ospho is acceptable, is it optimal? You can achieve the same benefits (conversion / etching) whether you rinse or not. I don't see how leaving it on could do anything but potentially compromise your work.
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Old 01-23-2020, 11:31 AM   #17
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I initially used Rustoleum primer on a piece of galvanized sheet I put up to cover my SCHOOL BUS sign in the back. A couple of days after it dried I was able to scrape it off with my fingernails. It also then wiped off completely just with a rag and mineral spirits - so at least it was easy to fix the problem.

I instead used Rustoleum self-etching primer and that has held up very well. SEM self-etching primer works well, too.
Hmmmm.... This makes me pause, I've been using KEM Bond (marine metal primer) on my floor and well the fumes still haven't subsided that much and the other day I spelled a little thinner while cleaning a brush and it came right up...

Having no real experience with painting I have no idea if what I'm doing is right or wrong. And the time and money put into it so far makes it a hard pill to swallow if I'm doing it wrong.
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Old 01-23-2020, 02:03 PM   #18
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Truthseeker, this should be the data sheet of what you used. Confirm that's the case though:


https://www.paintdocs.com/docs/webPD...&prodno=B50NZ3


2 things: Steel does not mean galvanized steel (might as well be 2 different metals as far as paint goes), & even w/ steel it sounds like you really need to prep the surface well for this to adhere. If you didn't acid-etch (ospho, as per the discussion above) I wouldn't be surprised if you have adhesion problems. That being said, I don't think coming up with thinner would be unexpected. It's a single-part (non-catalyzed) paint, so it's always going to be susceptible to the right thinners. It's meant to be top-coated. The clean-up directions specify using thinner. Also, as a single-stage, solvent-borne paint (the paint 'hardens' exclusively by solvent evaporation), it's probably not unusual for it to be off-gassing for some time. You might speed it up w/ forced ventilation.
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Old 01-23-2020, 02:48 PM   #19
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Very glad I read this before I started painting the deck ;)

(That's Navy for floor)
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Old 01-23-2020, 04:27 PM   #20
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a plain old white vinegar wipe down will take the coating down enough for the paint to adhere on galvanized areas especially new metal that you want to prep for paint.
still need an ospho or something of that nature for the rusty areas
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