Zinc Vs Galvanized Hardware - Which is better?
Zinc - the Great Protector
This is the same type of galvanized fence as in the picture above. This galvanized fence post near Los Angeles is beginning to rust.
The protective zinc coating is used up and now the steel is rusting. Thorough cleaning and painting with a zinc rich paint will restore the appearance. These are often sold under then name "cold galvanizing".
Be a careful shopper - some "zinc" primers contain zinc oxide. You don't want zinc oxide. This is an inexpensive white pigment. You want pure zinc. "Cold Galvanizing" paint is probably going to contain pure zinc.
Another method of protecting this fence would be to attach zinc anodes to the fence at regular intervals. Small zinc anodes should be available at boating supply stores near the ocean.
There are two cautions when restoring this fence. You probably don't want to "sand blast" it to remove all of the corrosion and white zinc oxide as you will also remove what galvanizing is still there. But if you don't remove all of the rust and oxides than a barrier paint will not stick.
A paint barrier will soon crack and peal and allow water to travel under the paint. The paint film will then accelerate corrosion by trapping water salts. Paint will make your fence look good for that party next week - but in a few years might look awful. Use a zinc rich paint. One trick from the aircraft industry when using zinc chromate primer was to apply it thin. You should be able to slightly see through it and then don't apply a topcoat paint. This way you get the zinc protection without paint pealing or sealing water under the paint.
Comparison of painted steel versus galvanized steel. The rusted bracket was welded onto the galvanized pole. The bracket was painted and not galvanized. Its too late to galvanize the bracket but light sanding and a zinc rich primer, such as "cold galvanizing" would last longer than paint. Decorative paint can be sprayed over the zinc.
Paint protects by providing a protective barrier. But as soon as the paint film is scratched, or at sharp edges, moisture enters and causes rust and corrosion.
Zinc protects by sacrificing itself - Ships attach large blocks of zinc to the hulls to protect the hull from corrosion. This is called a "sacrificial anode". Galvanizing covers your part in a thick sacrificial anode. Zinc is also able to protect at a distance. All of the surface need not be covered with zinc as is true with paint. Ships need not cover the hull with zinc anodes. They are placed near and in electrical contact with the hull.
You go to the hardware store and there is the bolt you need - zinc plated or galvanized - which should you purchase.
Zinc is pretty and shiny - galvanized is dull and ugly. But wait, if you're using the bolt outdoors, in a few years that shinny zinc bolt will be ugly rusted and that dull zinc bolt will still look new.
Outdoors, and where you need corrosion protection - Galvanized
Indoors, or in dry climates where corrosion is not a concern - Zinc
What is the difference between zinc and galvanized? Both zinc plating and galvanizing applies a zinc plating. So they both use zinc. The big difference is in thickness, zinc plating is typically 3 microns thick. Hot dip galvanizing is 50 microns thick - so you get 10 times the protection with galvanizing.
Even after 20 years outdoors this galvanized fence shows no signs of rust. The Galvanizing has formed a white protective coating (patina) that adds to its protective properties.
All true galvanizing is hot dip galvanizing. The term "hot dip galvanizing" is used so there is no confusion over some paint companies who try to full the consumer by calling their product "galvanizing". Parts to be galvanized are submerged in molten liquid zinc, hence the name "hot dip."
Why not Paint instead of Galvanize?
Barrier Protection provided by paint is soon scratched exposing the unprotected metal. Ugly rust soon appears.
Moisture can travel under the paint and cause hidden rust and corrosion.
Barrier films, such as paint, leave crevices and edges exposed. Sacrificial zinc protection provided by Galvanizing or even a zinc rich paint does not need to cover everything to provide protection.
Zinc plating, Galvanize, Zinc rich paint, Zinc sacrifical anodes, all protect your property. One other zinc product that is extremely useful and you might not have thought of is Zinc antiseize. I apply it to bolt threads and other threaded fixtures in the yard.
Notice in this picture that the antiseize is thick and pasty. This is because it contains mostly zinc (43%). Some inexpensive antiseize is thinner. This is because it contains more oil and grease and less of the more expensive active ingredient. The best method of making sure you get good antiseize is to purchase antiseize that conforms to MIL-T-2361. This is where you can purchase this zinc rich antiseize.
This is a close-up picture of the door on a red VW bug.
Beat rust and corrosion by using Mechanic's Toolbox Software. This is a sample of the type of information contained in the RUST tool included in the software.
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