Compatibility of Powder Coating and Galvaniziation 1

[EngEquilibrium]

Hi,

I have a exterior pergola type structure that has both heavy timber and steel elements. The architect would like to powder coat the steel elements instead of galvanizing. The base plates need to be galvanized as they will be buried.

1. Can something be powder coated after it is galvanized? Or are the two processes incompatible? We want to make sure the base plates look the same as the rest of the structure without having to galvanize everything.
2. If I have a galvanized/stainless steel screw connecting the powder coated steel component to the timber components, is it okay for something that is galvanized to be in contact with something that is powder coated? Or will the two coatings/processes damage each other some how?

Thanks!

 

[dik]

I've seen it done both ways. You have to contact the coating supplier to confirm that the coating is compatible with HDG. Some coatings aren't. Some coatings are OK without HDG, but the supplier knows.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TugboatEng]

The powder coat won't adhere well to the galvanized metal. There is a process called galvannealing where the galvanized part is baked at high temperature and this promotes paint adhesion.

With that said, I'm really not a fan of powder coating. I don't know a lot about it, I've never called for it. I do know that it looks great until the entire powder coat coating pops off in one giant piece. I know that my experience may not represent the reality. The failures I have seen are probably the result of improper prep/application.

Sand blasting, inorganic zinc primer, epoxy primer, and polyurethane top coats add up to make the most weather durable and forgiving cosmetic coatings.

If you must coat HDG it can be etched with phosphoric acid. Again, I have not done this so I can't provide specifics.

There are flame sprayed aluminum coatings, metalizing that I believe tolerate top coats.

http://www.metalize.net/content/flame-sprayed-aluminum-coatings

 

[dik]

Hi Tug... I've seen it done both ways. With some coatings, there is a zinc saponification that occurs and bonding is prevented.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TugboatEng]

That is a novel (to me) terminology and has brought up some interesting papers. Thanks! I don't deal with hot dip galvanized in the marine industry very often but I think could be beneficial when paired with the correct coating process. It's much less expensive than painting and gives a good life expectancy on most structures. Combining it with paint provided you can get it to stick would be ideal.

 

[dik]

I've even used coating systems (safety yellow) with stainless steel as well as HDG. You often can see where HDG coatings have failed for the reason the coating didn't work well with HDG.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TugboatEng]

Azko-Nobel (AwlGrip) has a primer for both aluminum and SS painting (they're both subject to crevice corrosion). This primer would probably work well for HDG provided you can stomach the price tag.

https://www.awlgrip.com/products/primers/wash-primer-cf

 

[hokie66]

Suggest asking this question in the Paint/coatings engineering forums. There are some knowledgeable boffins there.

 

[dik]

Thanks, Tug... that's the product I used... great stuff. It was for a mining project and the client had ample funds and there's a lot of abuse on site. Haven't heard of any complaints.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EdStainless]

Another coating system that I have some familiarity with is this:

https://www.uscoatings.com/blog/vsc...-coating-with-superior-long-term-performance/

It is fantastic and very durable.

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P.E. Metallurgy, consulting work welcomed

 

[dik]

thanks Ed... can you use this with HDG?

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EdStainless]

I believe so, they have a couple of different primers for this so I presume that one of them would be suitable for HDG.
Getting the HDG clean is sometimes the biggest problem.

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P.E. Metallurgy, consulting work welcomed

 

[EngEquilibrium]

Hi, Thanks everyone for the great feedback and various options available out there. I did not know there was a paint/coating forum and will ask the question there to get even more options.

 

[dik]

Thanks, Ed... a really good thread... a BPS to the OP for the question.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[kingnero]

Consider metallization (I don't know if that's the correct terminology in English - It's basically a zinc/aluminium wire that is pulverized using high heat (acetylene flame) and projected onto the object using compressed air) with power coating on top.
In many cases, a better choice than HDG + power coating.

 

[dvd]

Never have painted, nor powder-coated, hot-dipped galvanized steel, but have worked with galvanizers who indicated that it improves corrosion resistance of galvanizing.

Preparing HDG for Powder Coating

 

[dik]

Paint coating over HDG is not often done, including for stainless steel. I usually spec that bollards are painted safety yellow... HDG or SS. Metallizing is good, albeit pricey, and they often use it for bridge repair in these environs.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[hokie66]

Coating of HDG is common. I don't know why you would say it is not. The link by dvd has a section on painting HDG steel.

Some architects tend not to like galvanizing, because it leaves an irregular surface. That surface then requires preparation if a smooth surface finish is to be achieved with coatings.

 

[dik]

About 95% of the stuff I do, HDG is left by itself... by not common, I mean the 5% that is coated.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EdStainless]

But remember that nearly all of the exterior body panels on your car on either one side or double sided galv.
Just depends on the industry/application.
Question: What is your experience with shallow burial of HDG?
I had always thought that this was not a good idea, but I am not sure.

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P.E. Metallurgy, consulting work welcomed