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Old 05-15-2020, 01:10 PM   #1
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What Paint

I have began to start thinking about painting my bus. I have a 2003 Chevy shortie with a roof raise. I also replaced some of the windows with sheetmetal. All of the sheetmetal I used for the raise and the windows is galvanized sheetmetal. Now I am trying to figure out the best combo of primer/ paint that is also compatible with galvanized sheetmetal. It sounds like oil based might be out due to the galvanized. Does anyone have any experience painting galvanized.

Also I need to seal my roof raise transition. I was thinking about using Sika or a similar polyurethane caulk and then paint over the entire roof with a roof sealant paint. Does anyone have any suggestions for sealing/ painting the roof?
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Old 05-15-2020, 02:43 PM   #2
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From my research, there's not much out there that claims to work right out of the box (bucket?) on galvanized. Even paints specifically marketed as being made for galvanized generally require special surface prep, which usually includes etching with phosphoric acid (ospho), followed by an aggressive clean-water rinse to rid the surface of any remaining acid. Many people don't read and/or follow the TDS (technical data sheet). If a given paint is compatible with galvanized, it will be stated there, as well as the specific procedure for prep. I'd follow such instructions to the letter.

We actually just received most of the paint for our exterior. We're going with Axalta Corlar 2.1ST epoxy primer, over which will go Imron 3.5hg+ polyurethane. The primer is direct-to-metal, as well as being compatible with many cured coatings, so I expect it to work great for the mix of the two I'll be coating. It's also a mastic (high build, sealing) primer - suitable for waterproof sealing (immersion) given sufficient film thickness - so it should work great for sealing up any hair-width invisible cracks that may be present around rivets & seams. Per the TDS it's good on galvanized (so long as prep is done). The cost is lower than most automotive-specific 2K products with similar properties.

Another big plus on both the primer & paint is that - unlike many other industrial / automotive 2-part products - the TDS includes specific instructions, and Axalta makes special reducers & additives, for roller/brush application. Most of these types of paints don't, so this was pretty big to us. Not only is spraying impossible where we're at (overspray concerns), this **** is nasty (health-wise). Rolling makes it way safer (though we'll still be wearing full PPE applying it). How it will turn out I can't say, but we're more concerned w/ durability than appearance, so if it isn't perfect, no sweat. We're going to try something akin to the 'roll & tip' method popular among boat builders to hopefully get a somewhat decent look. Another huge plus regarding the Imron is that you can recoat over cured paint without any surface prep other than cleaning. Not many such paints can or do make that claim. Should be a benefit for keeping it looking & protective well in the years to come with minimal hassle.

A great product (per the specs) for sealing seams, painted or bare, that you never want to come apart is 3M FC550 adhesive/sealant. But I stress the never come apart bit. We'll be using 3M automotive seam sealer (or dynatron 550... maybe the same thing?) for stuff that may need to come apart sometime in the future. All are polyurethane based, & paintable.

I'll be painting the roof here w/in the next 2 weeks unless something goes very funky. I'll post my impressions / observations in our build thread (see our sig line) when that happens.



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Old 05-15-2020, 05:51 PM   #3
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@Danjo painted his bus recently & it turned out tits. Might want to hit up his threads for input / advice.
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Old 05-15-2020, 07:49 PM   #4
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You need to use a self-etching primer with galvanized. I covered my rear school bus sign with a big piece of galvanized sheet metal and used Rustoleum self-etching primer which adhered very well. I've also used it on the galvanized metal of my diesel tank.

The annoying thing is that it seems to be only available in spray cans. At one point with my fuel tank I found myself spraying primer onto a roller so I could get at an otherwise inaccessible side of the tank. I'd like to find a comparable substance in regular liquid paint form.
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Old 05-15-2020, 09:45 PM   #5
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Originally Posted by TheHubbardBus View Post
@Danjo painted his bus recently & it turned out tits. Might want to hit up his threads for input / advice.
Haha. Thanks. Itís a 20/20 paint job. I guess itís OK for a first attempt.

The one thing I did get right, I think, is using the right products. I went single stage.

Great materials, total noob spray gun operator.

I had good luck with PPG for their tech support and good documentation. They took all the questions out of product compatibility and method of application. BUT the local supplier wasnít as good as the backing company for anything. End the end they were just a supplier and I relied on the manufacturer for info.


Sorry I canít be more help, other than That I think single stage automotive paint is the way to go. Call PPG and Axalta. They both have great tech support.
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Old 05-15-2020, 09:58 PM   #6
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We have used the PPG AUE-300 series of implement paint. It does work well.
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Old 05-15-2020, 10:22 PM   #7
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https://us.ppgrefinish.com/PPG-Refin...leet-Essential

Here’s the link to the PPG Delfleet Essentials line. This is what I used. Check out the primers section for compatibility with galvanized
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Old 05-16-2020, 06:25 AM   #8
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Originally Posted by musigenesis View Post
You need to use a self-etching primer with galvanized. I covered my rear school bus sign with a big piece of galvanized sheet metal and used Rustoleum self-etching primer which adhered very well. I've also used it on the galvanized metal of my diesel tank.

The annoying thing is that it seems to be only available in spray cans. At one point with my fuel tank I found myself spraying primer onto a roller so I could get at an otherwise inaccessible side of the tank. I'd like to find a comparable substance in regular liquid paint form.
a quick wipe with some mild ospho solution and galvanized can be painted 24 hrs later.
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