EvanR
EvanR HalfDork
10/6/13 5:29 p.m.

Quickie:

When painting galvanized steel, should I prime first, or does the galvanization act as primer?

Thanks

JG Pasterjak
JG Pasterjak Production/Art Director
10/6/13 6:17 p.m.

Painting galvanized is a pain in the butt. Trust me on this one. Bottom line is you're not going to get anything to stick well without a lot of prep, and you're not going to get anything to stick at all without at least some prep.

The main frame of the camera dollies I build is galvanized steel tube. To prep them, we (well, my dad) washes them with a dilute vinegar solution, then gives them a quick pass on the wire wheel to give the surface some texture. We then use a zinc primer, and an epoxy enamel on top of that. it sticks pretty well, but is still prone to chipping.

In the past, I've used plasti-dip with some success as well. Use it as a base coat then go over top with an epoxy enamel.

The hot tip used to be spray latex, but they don't make it anymore. Latex sprayed from a gun might work, though.

jg

Toyman01
Toyman01 GRM+ Memberand UltimaDork
10/6/13 6:18 p.m.

If it's new galvanizing, it needs a etching primer. Nothing likes to stick to new galvanizing. If it's old galvanizing, I would still prime it but it doesn't have to be a etching primer. If you have time, let it age for 6 months to a year. It's a lot easier to paint.

EvanR
EvanR HalfDork
10/6/13 8:31 p.m.

well, poop.

I need really thin gauge steel, something that's so thin I can bend it without a brake. I found the perfect stuff, already bent, in the roofing department at HD. Too bad it's galvanized.

Time for Plan B.

fritzsch
fritzsch HalfDork
10/6/13 8:51 p.m.

Why do you need to paint it?

EvanR
EvanR HalfDork
10/6/13 10:03 p.m.
fritzsch wrote: Why do you need to paint it?

Because I'm using it as a trim molding.

fritzsch
fritzsch HalfDork
10/6/13 10:14 p.m.

I am not sure it will work for your application but what about anodizing? Might not be worth your trouble though

jmthunderbirdturbo
jmthunderbirdturbo Reader
10/7/13 4:06 a.m.

is it completely unreasonable to run a sanding wheel over it all and strip the galvanizing? then prime paint done? or are we talking yards of square footage...?

-J0n

moparman76_69
moparman76_69 Dork
10/7/13 6:08 a.m.

You can sand it but you don't want to breathe or leave any dust that can be breathed in later.

fasted58
fasted58 PowerDork
10/7/13 7:04 a.m.

I know a lotta you guys don't like the stuff but Muriatic Acid will strip the galvanized down to bare metal.

Soak in a plastic pan or brush on.

Work outside, breeze preferred, DO NOT BREATHE THE FUMES, it can knock you on yur ass... but it cleans extremely well.

Works on Zinc and Cad plating as well. Excellent weld prep on rusty metal too. DO NOT use on aluminum.

Javelin
Javelin GRM+ Memberand MegaDork
10/7/13 12:28 p.m.

Ooh, ooh, ask the guy that sells steel for a living!!!

It depends on the galvanizing. Standard galvanized (with "spangle") is coated with zinc in a "hot dip" process. This is a thick coating that leaves a satin, greyish surface. Electrogalv is the same coating, only applied differently, and much, much thinner. This is typically "brighter" and reflective. Neither is suitable for painting whatsoever. Not only will paint not stick to the coating, but sanding the coating is hazardous and you might as well just use regular old hot roll steel (mild steel) if you do that.

Now, Galvalume (or Algalume) is galvanization with 55% aluminum and 45% zinc. Galvalume is much better suited to painting and corrosion resistance. As a bonus, it has some heat-resistant qualities. This is fairly easy to find and only slightly more expensive than regular galvanization.

Lastly is Galvannealed or "Satin Coat". This is a regular hot-dip galvanized 9all zinc) that's immediately heat treated (annealed), which alloys the steel with the zinc. The finish has no spangle and is a dull matte grey finish. This is the galvanization that car manufacturers use. You can weld it and paint it with no ill effects whatsoever. It is also extremely durable, being an actual alloy. This is more expensive, but well worth the money.

Evan: try finding a local to you metal sales place, either a supplier (like what I work for) or a sheetmetal shop. You should be able to buy Galvalume all the way down to 30 gauge (it's very common in the steel siding/roofing industry) and Galvannealed down to 22 gauge.

Hope that helps!

bravenrace
bravenrace UltimaDork
10/7/13 12:31 p.m.

We paint and powder coat Galvaneal, and don't have any adhesion problems.

fanfoy
fanfoy HalfDork
10/7/13 12:40 p.m.

The few times when I've had to paint galvanized steel (for aesthetic reasons), I've used the special Tremclad (rustoleum) primer for it.. If you value your health, don't mess with the old techniques (sanding, acids, etc).

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