Painting an old galvanized trailer?

[Condor1970]

On a whim, I decided to paint my galvanized trailer. I have a couple quarts of Navy Blue Marine Topside paint from Rustoleum. Tough stuff, and works well on just about anything, like the Professional paint does. However, I found out you should use a water based primer on galvanizing, because the paint won't adhere to zinc.

Well, I did a small test area with this paint, without even using primer. I just wanted to see how the color would look. I let it dry for a week, and scratch tested it. It is pretty tough, but like any oil base, will scratch if you rub hard enough. What I found interesting, is that I pressure washed the trailer, and not so much as a chip of paint came off. What I don't get, is why it is sticking so good, when everyone says it won't. All I can think of, is that this trailer is 25 years old, and has been outside most of that time, and even has a couple small rust spots here and there. Nothing major though. It still ooks pretty good, but there is some surface pitting in the galvanizing in various places too. Maybe due to age, the galvanizing lifespan is coming to an end, and painting it would actually be a good idea in this case.

Any thoughts or suggestions on this?

 

[dingbat]

Paint doesn't stick to zinc????? Car manufacturers don't seem to have a problem painting over the galvanized (galvanneal) body panels of a car.

Long life. The life expectancy of galvanized coatings on typical structural members is far in excess of 50 years in most rural environments, and 20 to 25 years plus, even in severe urban and coastal exposure.

Automatic protection for damaged areas. Galvanized coatings corrode preferentially to steel, providing cathodic or sacrificial protection to small areas of steel exposed through damage. Unlike organic coatings, small damaged areas need no touch up. Complete protection. Every part of a galvanized article is protected, even recesses, sharp corners and inaccessible areas. No coating applied to a structure or fabrication after completion can provide the same protection.

 

[bajaunderground]

I seem to remember when painting galvanized metal, you need to neutralize the zinc coating with a weak acid. I know we used white vinegar as a neutralizer and then painted? Not sure of the paint, but I believe it was a spray enamel? Call the manufacturer of the paint and ask?

 

[UncleWillie]

The paint will stick to the galvanizing initially.
Don't expect it to start peeling for a year or maybe two.
You may regret the decision in five years when it becomes a peeling mess.

 

[midcarolina]

Old galvanized steel has been passivated by weathering....... any factory applied coatings are long gone, as long as you cleaned prior to painting as you would any thing........you should be fine.

 

[Condor1970]

I thought one of the main reasons paint doesn't like Galvanized surfaces, is the oil impregnated into the zinc dip. My thought, is that even though the zinc is still on the surface protecting the metal, all that impregnated oil is long gone after years of weathering. Thus, the paint will adhere at this point.

Does this make sense?

 

[bruceb58]

The problem is that there is a layer of zinc oxide that is covering the zinc. Paint doesn't like to stick to that. If you can get that off, the paint should stick fine.

 

[bruceb58]

The problem also is that there is a layer of zinc oxide that is covering the zinc. Paint doesn't like to stick to that. If you can get that off, the paint should stick fine. The paint manufacturer should have directions on how to prep.

I actually wish I had a galvanized trailer so I WOULDN"T have to paint it.

 

[Mel Taylor]

Old galvanized steel has been passivated by weathering....... any factory applied coatings are long gone, as long as you cleaned prior to painting as you would any thing........you should be fine.

I'm now retired but spent many years painting industrial sites and equipment of all kinds including lots of galvanized metal, and I totally agree with midcarolina.

 

[dingbat]

The paint will stick to the galvanizing initially. Don't expect it to start peeling for a year or maybe two. You may regret the decision in five years when it becomes a peeling mess.

Auto companies seem to have solved the problem......

 

[dingbat]

Painting "galv" isn't overly complicated if you know what product you dealing with and use the right process and product.

Galvanize is a generic term for 30+ different metallic based, sacrificial coatings. The coatings are applied either by dipping the substrate in a molten bath of the sacrificial alloy or electrode-deposited. The surface is then further processed to produce the required texture.

Choosing a method to paint a galvanized surfaces primarily depends on the method of coating. Hot dip tends to produce a "rough" surface texture. Electrode-deposition tends to produce a glass like surface. Paint is going to adhere poorly to the surface no mater what you do.

 

[Okieboatguy]

I had the same question a few years back, and this is what I found on the AGA (American Galvanizers Association) web site; [h=3]Fully Weathered[/h] Fully weathered galvanized steel has zinc compounds covering the entire surface. The main compound in the fully weathered surface is zinc carbonate. Zinc carbonate is tightly adhered to the surface, is not water soluble, and does not wash off the surface when water hits the part. In this state, the zinc compounds should not be removed, as the paint performs better when the compounds are left on the surface. Fully weathered galvanized coatings are the simplest surface condition to paint, as only mild cleaning is necessary. This condition is present from one year of exposure to the atmosphere until all the zinc coating has been consumed by protecting the underlying steel, which will take decades.

The AGA website link: http://www.galvanizeit.org/specific...ifying-duplex-systems/preparing-hdg-for-paint