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View Full Version : OT, painting galvanized, what is the best way, experiences, tips



RussZHC
03-27-2016, 08:29 PM
Got a metal stand to paint up, most is mild steel but there are a couple of pieces of galvanized, stuff from back in the '50s.
Previous coating of paint was just flaking off, a stiff nylon brush with next to no elbow grease so don't want to duplicate that effort.

In a previous life working in autobody, we had most of the metal and coating combinations figured out, if not great at least so the coating would last a few years or longer...have no recall as to what we did with galvanized.

What have any of you found to work the best?

Is that green phosphate primer going to help? Cleaning with a particular variety of cleaner? Priming, and if so, with what?

It is not a "must paint" but would be nice if the stand could all be one colour, not a big fan of "aluminum" paint or I would just do that...

Oh, its going to be sitting inside its whole life so its not like a antenna or light post weathering.


Thanks,
Russ

rkepler
03-27-2016, 08:41 PM
I painted some galvanized with a prep from Rustoleum called "Galvinoleum". It's not a galvanizing but an undercoat that sticks to the zinc and provides a surface for the paint to stick to, in my case an alkyd enamel. It's been there for almost 10 years with no problems.

wierdscience
03-27-2016, 09:22 PM
Here it is from the source-

http://www.galvanizeit.org/images/uploads/articles/paintsteel.pdf

kitno455
03-27-2016, 09:27 PM
We used to paint galvanized sheet after first etching the surface with white vinegar, don't recall any problems.

allan

_Paul_
03-27-2016, 11:22 PM
My Painter friend tells me that Calcium Plumbate should be used on Galvanized items.

Paul

Illinoyance
03-27-2016, 11:40 PM
Plumbate....
Does that refer to a lead compound?

RussZHC
03-28-2016, 12:20 AM
Calcium Plumbate

Not doubting what you were told but is this still available?
Asked as all info I can find refers to it as a "lead based primer"...in fact some discussions are about whether red or white lead is better as its additive...and some of the usages referenced go back to the mid- 1960s.

Again, not doubting,
first etching the surface with white vinegar and my organic chem is certainly lacking but isn't that an acid? Discussed references are almost entirely dealing with alkyd solutions in the range of a pH of 12 (or have I got that backward, that is the number just can never remember higher is more basic or more acidic)


a prep from Rustoleum called "Galvinoleum"
given its other suggested uses, mainly smooth hard surfaces, suspect that among other things it is an etching compound (so physical improvement of the surface for mechanical attachment of paint as opposed to just a cleaner and thin layer of "neutralizer")

Good info, thanks all.

cameron
03-28-2016, 02:04 AM
Again, not doubting, and my organic chem is certainly lacking but isn't that an acid? Discussed references are almost entirely dealing with alkyd solutions in the range of a pH of 12 (or have I got that backward, that is the number just can never remember higher is more basic or more acidic)



.

Just to avoid confusion, I think you meant to write "alkaline solutions". Alkyd resins are used as binders in paints.

The reference cited suggests using an alkaline solution for removal of dirt, oils and greases. It should then be thoroughly rinsed from the surface. Not mentioned is that alkali left on the surface could react with oils and resins in the paint to produce a thin layer of a soap at the interface of the metal and the paint, resulting in poor adhesion. (Actually, that last bit is just my opinion, and not based on any experimental evidence of which I am aware)

Recommendations to apply various acids to etch the surface of the zinc go back a long way. For example, the 1973 edition of the Standard Specification for Highway Bridges specifies, after weathering of the surface for as long as possible:

Before painting galvanized surfaces, they shall be treated as follows:
In I gallon of soft water dissolve 2 ounces each of copper chloride, copper nitrate, and sal ammoniac, then add 2 ounces of commercial muriatic acid. This should be done in an earthenware or glass vessel, never in tin or other metal receptacle. Apply the solution with a wide flat brush to the galvanized surface, after which it will assume a dark, almost black, color, which on drying becomes a grayish film.


How effective that is, I don't know. It almost sounds as if someone threw a bunch of stuff in the pot in hopes that one or more of the ingredients might do some good.

Richard P Wilson
03-28-2016, 04:26 AM
Just to avoid confusion, I think you meant to write "alkaline solutions". Alkyd resins are used as binders in paints.

The reference cited suggests using an alkaline solution for removal of dirt, oils and greases. It should then be thoroughly rinsed from the surface. Not mentioned is that alkali left on the surface could react with oils and resins in the paint to produce a thin layer of a soap at the interface of the metal and the paint, resulting in poor adhesion. (Actually, that last bit is just my opinion, and not based on any experimental evidence of which I am aware)



Recommendations to apply various acids to etch the surface of the zinc go back a long way. For example, the 1973 edition of the Standard Specification for Highway Bridges specifies, after weathering of the surface for as long as possible:

Before painting galvanized surfaces, they shall be treated as follows:
In I gallon of soft water dissolve 2 ounces each of copper chloride, copper nitrate, and sal ammoniac, then add 2 ounces of commercial muriatic acid. This should be done in an earthenware or glass vessel, never in tin or other metal receptacle. Apply the solution with a wide flat brush to the galvanized surface, after which it will assume a dark, almost black, color, which on drying becomes a grayish film.


How effective that is, I don't know. It almost sounds as if someone threw a bunch of stuff in the pot in hopes that one or more of the ingredients might do some good.

Sounds like the stuff we called 'British Rail T Wash' here in the UK, which for many years was the standard stuff specified in public contracts for coating galvanised steel before painting.

Chris Evans
03-28-2016, 06:13 AM
As another UK input we use a product known as Mordant T wash. I use it on replacement Land Rover chassis prior to painting. Sounds like the same as your British Rail T wash stuff.

Fasttrack
03-28-2016, 09:20 AM
I did a bunch of research on this in years past. I've forgotten many details but a few big points stuck with me:
1) Weathered galvanized surfaces (e.g. exposed to the outdoors > 1 year) will accept a high quality paint fairly well. Just clean the surface well as you would with any surface about to be painted.
2) Self-etching primers work well on newer galvanized surfaces. I've had good success with Eastwood and Duplicolor self-etching primers. They even work improve top coat adhesion on difficult materials like stainless steel and aluminum.

SteveF
03-28-2016, 09:59 AM
It was a while since I painted some galvanized metal and don't remember what I used. But I know this, make sure to thoroughly read the manufacturer's information because most primers specifically say "Not for use on galvanized metal". When I went into the local Duron industrial paint distributor and asked for a primer, the guy says "Here's what you want to use, works great on galvanized metal". Flipped the can around and noted that it said "Not for use on galvanized metal" right on the can. Read the manufacturer's info and ignore everything else.

Steve

bob_s
03-28-2016, 01:59 PM
Zinc-chromate based primer.

old mart
03-28-2016, 02:56 PM
Just degrease it well and splash on some hammerite.

RussZHC
03-28-2016, 05:19 PM
Just degrease it well and splash on some hammerite.

this one is what I ended up doing this morning, will see how long it lasts (as I said, its whole life should now be indoors so not under a lot of stresses)...more a function of what I had on hand when it was ready to go...

I will have to revisit this coming up as I know there are numerous posts at work where the paint is flaking and my suspicions are galvanized.
When its on someone else's tab, going to try the cleaning as today, then either etching or zinc-chromate prior to top coating.