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Old 07-09-2019, 12:20 PM   #1
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Etching new galvanized metal with Ospho

OK, so I'm painting my floor and getting ready to patch the holes, and a couple of thin spots, too. Yesterday I got several small pieces of new galvanized varying from 20 to 24 gauge, and now I'm cutting them to size, making patches without sharp corners. I intend to paint them and then epoxy them down to the already painted floor

I've read a number of threads on the forum here about using Ospho particularly looking for info on etching galvanized with Ospho before painting. I found at least one that mentioned immersing the metal in Ospho rather than spraying of brushing it on, but I didn't see anything about how long to soak it. And I found at least one thread that mentioned diluting Ospho before using it, but I did not see anything about how much to dilute it. I have about a quart left, so I need to be careful about diluting it too much or I will end up having to buy more.

So I would appreciate any comments from anyone who has experience using Ospho on new metal that is not rusty just to etch it before painting. Comments and opinions will also be appreciated. Thanks in advance, Greg
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Old 07-09-2019, 12:36 PM   #2
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Not sure why you chose galv. steel to patch your floor Greg, but it's my understanding the ospho actually eats away a bit of the galv coating to where primer/paint will stick to it.

If it were mine and I only had galv to work with vs plain cold rolled sheet metal, I'd epoxy the various cut up patches to the areas that need patching, in its "raw" state. Then, once the epoxy has had time to set up, I'd use 3M spray undercoating on them instead of trying to prime/paint the finished patches.

They will all be covered so no need to get "pretty" with various topcoats on the finished product, and the undercoating is plenty durable and provides a small level of sound deadening to the now covered area.
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Old 07-09-2019, 12:57 PM   #3
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I chose galvanized because the floor is galvanized. Around 50 percent of the original zinc coating is still intact even after receiving quite a bit of attention from a 4.5 inch wire brush on my angle grinder, then being osphoed with a mop and bucket, and finally liberally hosed down and scrubbed with a well-worn old corn broom.

I can be a bit of a perfectionist at times, but I see the metal floor as a vapor barrier, and I want it sealed tight. I intend to epoxy pre-painted patches to the already painted floor, and I will then put a final topcoat on after gluing the patches in place with slow-curing epoxy.

And I should add that my bus was well undercoated when it was new and then spent it's whole life near Seattle where I don't think they use any salt. The only rust on the bus was on top of the floor because several windows leaked quite badly. As far as I can see from crawling around underneath the bus, the factory undercoating is still intact and doing it's job. So my bus is not rusty underneath, and I'm not inclined to mess with it.
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Old 07-09-2019, 01:10 PM   #4
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Degrease then distilled vinegar
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Old 07-09-2019, 01:18 PM   #5
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@ Danjo, thanks for your suggestion. I do have a jug of distilled vineagar sitting around since I bought the wrong kind for pickles.

Degrease with what exactly? I'm trying to avoid a trip to the store, Would acetone on a rag work?
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Old 07-09-2019, 01:40 PM   #6
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That'll work but mineral spirits (paint thinner) followed by a detergent wash and vinegar will work even better. After the vinegar treatment the galvanizing should have greyish white cast and little or no shine. Oh, remember to rinse the vinegar off or the paint won't stick.
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Old 07-09-2019, 02:07 PM   #7
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Thanks very much, Jack, that makes it very clear. I will use the vinegar and save the Ospho for when I really need it. And I just remembered I need to go buy some paint thinner anyway.
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Old 07-09-2019, 04:16 PM   #8
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Epoxy and pennies.
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Old 07-09-2019, 05:27 PM   #9
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Several people I know who are into hunting for coins with metal detectors have told me that the new style pennies will disolve in no more than 2 or 3 years just from the electrolytic effect of damp soil.

After all the work I've put into my floor so far, I want the patches to be as strong as the rest of the floor. To each his own, but it seems like false economy to me to use pennies, even if you find the older ones, which would be much better but have fun finding enough of them.
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Old 07-09-2019, 05:51 PM   #10
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Several people I know who are into hunting for coins with metal detectors have told me that the new style pennies will disolve in no more than 2 or 3 years just from the electrolytic effect of damp soil.

After all the work I've put into my floor so far, I want the patches to be as strong as the rest of the floor. To each his own, but it seems like false economy to me to use pennies, even if you find the older ones, which would be much better but have fun finding enough of them.
In 1983, forward, pennies have been minted from copper clad zinc slugs.
Circa '82 and earlier are pure copper, and are ironically worth more for the metal than their face value.
I used the latter to plug the holes in my floor. Easy enough, I've been collecting scrap scrip for years.
And I reckon it all depends on the soil type they were referring to. It can be dangerous to speak in absolutes like that. It's as if you made the blanket proposition that all politicians are lying, shifty, inflamed hemorrhoids.
OK, bad example...
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Old 07-09-2019, 06:57 PM   #11
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OK, so I'm painting my floor and getting ready to patch the holes, and a couple of thin spots, too. Yesterday I got several small pieces of new galvanized varying from 20 to 24 gauge, and now I'm cutting them to size, making patches without sharp corners. I intend to paint them and then epoxy them down to the already painted floor

I've read a number of threads on the forum here about using Ospho particularly looking for info on etching galvanized with Ospho before painting. I found at least one that mentioned immersing the metal in Ospho rather than spraying of brushing it on, but I didn't see anything about how long to soak it. And I found at least one thread that mentioned diluting Ospho before using it, but I did not see anything about how much to dilute it. I have about a quart left, so I need to be careful about diluting it too much or I will end up having to buy more.

So I would appreciate any comments from anyone who has experience using Ospho on new metal that is not rusty just to etch it before painting. Comments and opinions will also be appreciated. Thanks in advance, Greg
I actually just had to deal with this because I made a cover for the hole where the SCHOOL BUS sign used to be out of 26 ga zinc-plated steel. I originally just washed it and then sprayed it with automotive primer, but I could see immediately that something funny was going on with the paint.

Came back the next day and I was able to just spray the primer with mineral spirits and it scraped off easily, so it was definitely not adhering properly. I took off all the paint and then left a coat of Loctite naval jelly on it for a few hours (naval jelly is basically ospho with a gelatinous ingredient that helps it stick), then cleaned it off and sprayed on Rustoleum self-etching primer (the self-etching is the important thing).

It seems to have worked fine (although this was just a few days ago so I can't vouch for long-term success). Since you're doing your floor you wouldn't need naval jelly (horizontal pieces will hold the ospho better). You might even be better off soaking the parts for a bit in ospho to make sure you get a good etching all over.
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Old 07-09-2019, 09:15 PM   #12
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Well, my patches are not rusty at all, but they're going to get the same Rust-Oleum primer for rusty metal that I put on the floor. And I've been convinced to try vinegar instead of Ospho. I think Ospho will remove more zinc than necessary to roughen the metal so paint sticks to it, so I will use vinegar to etch the new galvanized patches and save the Ospho for something that really needs it, like the circa 1946 Craftsman tool box I used ospho on a few days ago. That old tool box got left out in the rain too many times, that's for sure.
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Old 07-09-2019, 09:20 PM   #13
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You mean I shouldn't have added that layer of damp soil to my floor? If the old pennies were't bad why are the new ones, they have the same surface? I would trust any penny and it's thickness over what the rotting floor is made of.
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Old 07-09-2019, 09:34 PM   #14
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Because the old ones were made out of one kind of metal, almost pure copper, in a chunk, but the newer pennies are a sandwich of a layer of zinc between two thin pieces of copper, a perfect situation for electrolysis. It's all very scientific.
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Old 07-09-2019, 09:51 PM   #15
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Uh...
Nevermind.
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Old 07-09-2019, 10:18 PM   #16
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Old 07-09-2019, 10:59 PM   #17
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Old 07-21-2019, 01:31 AM   #18
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That'll work but mineral spirits (paint thinner) followed by a detergent wash and vinegar will work even better. After the vinegar treatment the galvanizing should have greyish white cast and little or no shine. Oh, remember to rinse the vinegar off or the paint won't stick.
Jack
worked for me on clean (no rust) galvanized for the last umteen years. They also sell paint with a heavy zinc content for welded galvanized
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Old 07-21-2019, 10:19 AM   #19
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The paint on my new galvanized patches seems to have stuck well and passes my thumbnail test. I had one patch that was too big to fit in any container I had handy, so I just laid it out on the lawn with rags spread on it and poured vinegar on it a couple of times, the after a few hours I did the same thing to the other side. That passes the thumbnail test too. So thanks to those who suggested the vinegar.
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Old 07-21-2019, 03:35 PM   #20
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The paint on my new galvanized patches seems to have stuck well and passes my thumbnail test. I had one patch that was too big to fit in any container I had handy, so I just laid it out on the lawn with rags spread on it and poured vinegar on it a couple of times, the after a few hours I did the same thing to the other side. That passes the thumbnail test too. So thanks to those who suggested the vinegar.
to pass industry standards, untreated galvanized steel surfaces need to be washed down with toluene before painting - you might prefer to stick to wiping with vinegar after reading about the safety precautions needed to be taken and the possible nasty effects on human health - when painting galvanized steel doors in a hospital renovation, we had to set up a low air pressure area to be sure not the faintest whiff of toluene could be detected outside of the work area

https://www.worldofchemicals.com/422...p-reactor.html
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