Hot Dip Galvanizing

[HWooldridge]

Anyone ever galvanized a piece for use outside? I have a client who is asking what can be done to minimize rust on some gates and windows. I talked them out of stainless simply because I don't think the cost is warranted in our relatively dry weather so they countered with powder coat on mild steel. I don't think powder coat is much better than regular paint since it can chip and (I assume) is hard to repair so we started discussing hot dip galvanized. I know it is more common on the coast to protect against sea spray but our relative humidity averages less than 50 percent and we have over 300 days of sunshine per year. The bottom line is that they do not want any rust within the foreseeable future.

[Woody]

Hot dip galvanizing = molten zinc = very toxic fumes. All of that has been covered in previous threads.

To hot dip galvanize you need a tank of molten zinc that is big enough to dip the whole piece. The process does not lend itself well to small applications.

For outdoor work I have the material sandblasted, then paint with a high quality zinc based primer. Then two coats of paint and clear coat over the top of that. I did that with 40 foot of railing on my patio deck 6 years ago and there is no rust yet.

[ironrosefarms]

As for the use of powder coat, I have used it on motorcycle parts in the past and it wore very well with all the dirt, gravel and other junk hitting it regularly. It tends to be a pretty durable surface. Visually the big difference is powder coat tends to have a bit of an orange peel texture compared to enamel paints. It can be chipped but in my experience it takes quite a hit to chip it. Here is a website that gives the products they manufacture and their appropriate uses... Protech PowderCoats
The section for outdoor items such as fences is here Outdoor Powder Coating
Just some food for thought...

Edited October 2, 2008 by ironrosefarms

[Max Mulholland - Tetnum]

if you ar really dead set on hot dipping the gate you could send it out because the whole peice has to be done at once or it will rust at the joints

or jous go with the above mentioned solutions

[theimi]

Here at he Cape coastel area nearly any gates and fences used outside are hot dip galvanized, which is really one of the best and durable rust protections besides the use of non rust materials...
the fumes shouldn't be interesting for you as you do any welding or forging before you bring the parts to the galvanizing company. After galvanizing it can be coated as usual, you can keep the zinc finish or some folks etch the galvanized parts to achieve an "older" interesting look (for ex. see Paul Elliott FWCB Hammer & Tongs Artist Blacksmiths Online where you may find lots of pictures of etched galv. stuff)
the big disadvantage is, if you do forge work, the zinc will hide the texture of the metal.

hth

[John B]

Hot dip galvanising is usually carried out at a specialist company, and the quality can vary from company to company. It tends to hide details on forged areas. It also need time to cure before painting, or a chemical neutraliser before painting, or a special paint for the job.

An alternative is hot zinc spraying, again done by a specialist, or you can get equipment to do this yourself, it leaves a good finish on forged work that can be painted over directly.

Powder coating can be a problem if you have temperature changes as although it forms a hard surface, if through the expansion and contraction the finish seperates from the material surface, then condensation within the area can form, and the metal rust out from the inside. It is also a problem in that it does not always get full penetration into areas such as where collars and scrolls join, or scrolls welded to bars.

The choice you make must depend on the suitablity for the work it is to be applied to.

Any finish is only as good as how it is maintained and looked after.

[Jerry W.]

Hollis,
Southwest Galvanizing Inc in San Antonio, TX
This a link to Southwest Galvanizing Inc. They are located on Houston St. just outside of Loop 410 on the east side of San Antonio.
Hope this helps,
Jerry

[TASMITH]

One note of caution about galvanized steel to prevent rusting is the fact that if the galvanized coating gets damaged to the point that the steel beneath it is exposed, the steel will actually rust FASTER than steel which has not been galvanized. I'm not exactly clear on the whole chemical process, but it creates a battery effect with the zinc acting as an anode and the steel(iron in the steel) acting as the cathode or vice versa. It sets up an electric current flow between the two and causes the iron in the steel to deteriorate at a faster rate then just being exposed to air and moisture alone.

Terry

[mike-hr]

I did a bamboo railing from various sizes of black pipe earlier this year. I was going to get it hot dipped, but the foreman of the shop wanted me to drill 2 holes in each piece of pipe, so it wouldn't float in his tank. I asked if he could simply wire it down to the tank cage, but he thought that was a silly idea. I ended up getting it sandblasted, and used Sherwin-Williams Zinc Clad IV, two part manual zinc epoxy. It was a gooey mess, and slightly thicker than sub-zero 90 wt oil. I had to brush it on with a stiff chip brush. It turned out okay, because the brush marks added some nice grain texture to the bamboo. Might be ugly on fine scroll work, or detail stuff.

[theimi]

the drilling of holes in each pipe is necessary because of the pressure of the zinc while flowing through the inside of the pipes. These holes are essential at each end of any pipe otherwise the pipes will burst.
of course, if the pipes are not closed u dont need holes.
holes are also necessary at the joints.
If you dont want the holes visible you can do them inside.

don't know what that guy told you but i have done lots of hot dip galvanized stuff since im in SA and never heard that

Edited October 2, 2008 by theimi

[HWooldridge]

I'm not planning to apply the zinc myself nor will I weld on it after it's completed. The items will be completely installed and tested for proper functioning then disassembled for hot dip - if that is the way they want to go. I have been doing this for 25 years and paint has always worked well - never had a callback for surface finish failure. I will simply tell them to go someplace else if it gets down to an argument.

Thanks for all the input.

[ironrosefarms]

It was mentioned that powder coat doesn't handle temperature changes well. I used powder coat on valve covers, oil filter covers, engine tags, and exhaust fittings on my motorcycle. These parts would many times go from 20 degrees F to normal engine temperatures above the 200 F mark or in the case of the exhaust parts well above that. Never had a separation problem. Being sure the powder coat that is being used is the proper product for the job at hand is a big part in making sure it lasts long term. Check out the website I posted above, some of the breakthroughs they have come up with in the past several years in how flexible and adherent powder coat can be is amazing.

I hope you'll let us see the final result regardless of the method of preservation used...

James

Edited October 3, 2008 by ironrosefarms

[Ten Hammers]

I might comment on paint. I have used Van Sickle tractor paint ( red primer then black topcoat ) on archways for cemeteries and churches. Last I checked zero rust after 3-5 years. No I did NOT use drier and it took LONG time to dry. Worth the wait.

[Joe H]

We send out poles and beams for our signs to be galvanized every now and then, if the customer requests it. It's really pretty inexpensive, quite a bit less expensive having those same items powdercoated. It IS a real pain in the rear though.

If you decide to go that route you will need to consult with the galvanizer beforehand. Nothing can be sealed airtight, you will need holes at least 1" diameter at several specific locations. If anything is sealed it will burst from expansion from the heat, and the holes need to be large so the zinc can drain out quickly. You end up having to be creative figuring out ways to cover the holes. Also any tapped holes, or welded on nuts will have to be re-tapped after galvanizing, this has been a real pain for me in the past.

[John Martin]

I will never do anything with zinc, even if it is a safe enviroment. That piece could someday make it back to me for repair, or some other poor smith and cause damage, it's paint, oils, beeswax, and other finishes for me.

[Ferrous Beuler]

There is really no reason for a blacksmith of any experience level to get involved with any galvanized metal at all.

Totally avoidable and for good reason.

Blacksmiths never resort to galvanized for a source of purposely used material in their work.

We know better, stay away from it. Don't weld on it or cut it with a torch either.

R.I.P. Paw Paw.

Dan:(

[Daryl]

Hot-dip galvanising has many benefits for particular works. However, the more intricate the piece, the less likely the galvanise will be able to effectively coat the smaller crevices and sharp indentations. I have tried some roses in hot-dip with mixed results (not the fault of the people doing the galvanise), and those that turned out faired well. After galvanise, it is important to use an etching primer to aid adhesion of the subsequent paint; simply throwing tremclad on will not turn out well in a few years.
.
I hope this helps.

[Ice Czar]

I'm not exactly clear on the whole chemical process, but it creates a battery effect with the zinc acting as an anode and the steel(iron in the steel) acting as the cathode or vice versa.

Galvanic corrosion

A common example of galvanic corrosion is the rusting of corrugated iron sheet, which becomes widespread when the protective zinc coating is broken and the underlying steel is attacked. The zinc is attacked preferentially because it is less noble, but when consumed, rusting will occur in earnest.

.

The bottom line is that they do not want any rust within the foreseeable future.

traditionally institutional building materials didn't employ galvanized steel
(Churches, Hospitals, Museums, Government Buildings, Libraries, ect)
Predicting the service life of galvanized steel

in architecture when possible, copper is employed. In traditional decorative iron work, the silicates in wrought iron provided corrosion resistance
http://www.artmetal.com/project/NOMMA/WROUGHT.HTM
Iron pillar of Delhi - Wikipedia, the free encyclopedia

It has attracted the attention of archaeologists and metallurgists as it has withstood corrosion for the last 1600 years, despite harsh weather.

in that case its phosphates rather than silicates

personal recommendation (assuming mild steel)
hot patina "black rust" with Vanex Break-Through Clear Satin 50-0
(a protective oxide layer with a modern exterior latex layer, relatively easy to repair in need)

or simply paint

at least your not creating a toxic booby trap for the future (assuming someone even tries to fix it or re-dip it)
that when it does get past the zinc barrier will go to hell in a handbasket

or

build it out of stainless steel (as previously mentioned)


probably the most telling point here is that
as a gate, penetration of the zinc is pretty much a given in short order


;) Edited October 19, 2008 by Ice Czar