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Old 04-26-2017, 11:00 PM   #1
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To treat or not to treat (new galv steel)

Here's an interesting one for you guys...

We're replacing the entire metal floor. The last few days have been spent scraping up all the old adhesive that kept the original steel down.

So we have new steel that we plan on putting down in the next couple days.

The question is, should we put rustoleum down or just let it go?

And before you say to just put the paint down, new galvanized steel can be a real pain as far as getting paint to actually stick for long periods (think ~5 years). I have no way of knowing how long its been weathered.

What would you do?

Also, there will be undercoating going on from below.
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Old 04-26-2017, 11:16 PM   #2
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You cannot get paint to adhere to galvanized without etching it first. Properly etched and painted, it will last much longer than unpainted.

PS...there are also "Self Etching Primers" out there.
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Old 04-26-2017, 11:32 PM   #3
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Use Ospho to etch galvanized steel, then its paintable.
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Old 04-26-2017, 11:49 PM   #4
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****, all you need to do is etch it? Okay then, I stand corrected! Thanks guys.
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Old 04-27-2017, 12:09 AM   #5
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Does muratic acid work for that? I know they use it on unpainted metal roofing before they paint it.
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Old 04-27-2017, 06:29 AM   #6
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Does muratic acid work for that? I know they use it on unpainted metal roofing before they paint it.
I'm sure it would, but its real nasty stuff. Especially inside a closed area.
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Old 04-27-2017, 09:03 AM   #7
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I'm pretty sure that muriatic acid should NOT be used on anything galvanized. It will strip the zinc off completely.
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Old 04-27-2017, 10:23 AM   #8
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When someone builds a big barn they often wash the metal with muratic acid before painting. It's readily available at any pool supply store.

I've never used it myself. That is what people used before there were all these etching paints and stuff.
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Old 04-27-2017, 10:39 AM   #9
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Why not go stainless?
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Old 04-27-2017, 10:52 AM   #10
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probably because galv steel is half the cost of SS... and I'm guessing they're not made of money...
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Old 04-27-2017, 11:21 AM   #11
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probably because galv steel is half the cost of SS... and I'm guessing they're not made of money...
Ding ding ding! We really didn't want to replace it at all, but the stuff in the bus to start was paper thin. I pretty much destroyed it getting the plywood up, so there was no option.
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Old 04-27-2017, 11:23 AM   #12
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I use muriatic to clean the mill scale off of hot rolled steel and it is seriously NASTY stuff to work with. It can, however, be diluted and used to etch galvanized. Full strength it would be far too aggressive. Personally, I stick with "Self-Etching" primer for that sort of thing.

One other issue...anytime you do use muriatic...you MUST use a "stop bath" to prevent continued etching and rust. Baking soda and water will stop the acidic action. Big PITA as the soda must be thoroughly cleaned off before painting.
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Old 04-27-2017, 11:26 AM   #13
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I've done as much researching as I care to do at this point. Here is what I've found. Please correct me if you think I'm wrong...

Muriatic acid will remove all of the galvanized coating. (Tango just commented above, sounds like you can use it diluted)

Phosphoric acid (Ospho) is a better choice if you want to keep it.

After using Ospho, the ideal primer will be a high-zinc formulation.

I don't want to spend all day looking for high-zinc primer, so I'll probably just go with rustoleum unless it happens to be easy to get and cheap.
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Old 04-27-2017, 11:30 AM   #14
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Most all auto parts stores sell rattler cans of self etching primer. Cheap, easy fix for galvanized and aluminum (which also must be etched first).
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Old 04-27-2017, 11:32 AM   #15
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Most all auto parts stores sell rattler cans of self etching primer. Cheap, easy fix for galvanized and aluminum (which also must be etched first).
How many cans for 120 sq feet do you think?
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Old 04-27-2017, 12:23 PM   #16
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I'm pretty sure that muriatic acid should NOT be used on anything galvanized. It will strip the zinc off completely.
I've used it on HUGE boats before.
I HATE working with muriatic acid, bad.
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Old 04-27-2017, 12:25 PM   #17
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I've done as much researching as I care to do at this point. Here is what I've found. Please correct me if you think I'm wrong...

Muriatic acid will remove all of the galvanized coating. (Tango just commented above, sounds like you can use it diluted)

Phosphoric acid (Ospho) is a better choice if you want to keep it.

After using Ospho, the ideal primer will be a high-zinc formulation.

I don't want to spend all day looking for high-zinc primer, so I'll probably just go with rustoleum unless it happens to be easy to get and cheap.
Ace sells zinc oxide primer, but after ospho Rustoleum sticks fine. I've done the entire inside of my ceilings with Ospho and Rustoleum- and it GOOD.
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Old 04-27-2017, 01:17 PM   #18
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Ospho goes on really thin, so I bet you can do the whole bus with 1 gal.
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Old 04-27-2017, 01:34 PM   #19
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I have to remember to go to ace more. Home depot and lowes consistently disappoint me in selection and quality, meanwhile ace always has what I need.

Long story short, I got ospho and special primer (happened to be $8 off today which I'm happy about), plus they have solar flex which no one else seems to around here.
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Old 04-27-2017, 01:42 PM   #20
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Ospho goes on really thin, so I bet you can do the whole bus with 1 gal.
Absolutely. I've been using it HEAVILY on my build, and I've still got a half gallon. Thin isn't even the word- its the same viscosity as water, and goes on like water. On areas that aren't rusty and I just want to etch, I dilute with distilled.
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