Flux Core Welding Galvanized Steel 16 Things to Know

By Bill Byers / January 29, 2019
Flux Core Welding Galvanized Steel

You have a small job or even a larger weld to do on a piece that lives out doors.

Fencing, tubing or maybe a machine part.

You know it’s steel but if it has been outdoors and shows little signs of rust it may have been galvanized or galvanized and then painted over. You want to know, what to do when flux core welding galvanized steel.

How can I tell if the Metal is Galvanized?

You may well see the tell tale sheen, sparkle in sunlight that gives away the fact that the metal is galvanized. Or

you may have seen a scratch in the covering paint and see the galvanization below the paint.

Galvanized Steel

Example of Galvanized Steel

What is Galvanized Metal?

Galvanization is a process which puts a protective zinc coating onto steel although to protect the steel from rusting.

Similar to paint it forms a protective barrier between the steel and the air though galvanization goes further by providing electrochemical protection

What is that?

The zinc oxidizes in the air. This oxidization protects the steel even if the steel is scored down to the bare metal – the zinc coating will still protect the metal.

The galvanization is applied to the steel through hot dipping the steel into zinc or shot blasting – called dry galvanization.

Here are the 16 things to know when flux core welding galvanized steel, made simple.

1. MIG welding Galvanized Steel?

Yes, you can use the MIG process – solid wire and shielding gas. Choose the right kind of solid wire and shielding gas and you can do it.

Many use straight carbon dioxide as their shielding gas of choice because it is cheap, though it does produce a lot of spatter. Otherwise 75% Argon and 25% CO2 is another good option for shielding gas.

Solid MIG wire is not tolerant of contamination of the welding area, so be sure to prepare well, grind off all the galvanizing – two inches either side of the weld.

Otherwise, contamination of your weld when you are MIG welding with solid wire and shielding gas means porosity, poor penetration that can lead to your weld failing.

MIG Welding Galvanized Steel

MIG Welding can produce Poor Results with Porosity

If the metal is thin grinding off the galvanization may not be a choice you have.

And often the galvanized job is outdoors because that is where most metal is galvanized to protect the steel. Windy conditions outside can blow away your shielding gas causing a poor weld.

And clearly, you will have much more to carry with you to the site of the weld, not only your MIG welder. You have to carry a tank of shielding gas too and perhaps a barrier to protect your weld area from the wind if it is not a completely calm day.

There is a better way.

2. Flux Core Welding Galvanized Steel

Flux Core Wire Welding Is the preferred method.

Because, as a process it is more tolerant of contaminants such as rust (although it is always better to clean the area of oils and rust before welding) with the flux in the flux core bringing the contaminants to the surface of the weld to be burnt off in the air or trapped in the slag which is removed after welding.

Flux core wire is much better for welding ‘out of position’ which is more typical when you are welding outside. Flux core in these situations can weld better and faster.

And you get good penetration using flux core wire in your welder and no need for an additional tank of gas.

3. What happens when you Weld Galvanized Steel with Flux Core Wire?

Something extra happens while you are actually welding.

First it is worth understanding that zinc melts at 900 degrees Fahrenheit and vaporizes into zinc oxide at 1650 degrees Fahrenheit. Why is that important, well when you weld, steel melts at 2750 degrees Fahrenheit. A much higher temperature than zinc.

This means that as you weld;

  • the welding arc vaporizes the zinc by contact with air.
  • Welding burns the galvanizing off using the heat of the arc
  • the zinc coating is removed from the weld point
  • the vaporized zinc causes more welding fumes

4. How do you Weld Galvanized Steel with Flux Core?

Unless there is a thick zinc coating, flux core welding is the same process as welding non galvanized steel, you select your volts and the Amp output of your welder according to the thickness of the metal you’re welding.

Just be sure to change your MIG welder’s polarity setting from positive to MIG gun negative if you are swapping over from solid wire to flux core wire.

This is often overlooked and is essential to successful flux core wire welding.

The welding voltage may need to be adjusted to reduce spatter, you may need to take a tiny bit more time on your weld travel and stay a little longer in the weld pool.

Use the pull technique rather than the push technique as you want to burn off the zinc and you want a good slag covering to form, removing any contaminants out of the weld.

You may well need to stop more often to clean the MIG gun of welding spatter and the zinc oxide dust. Using anti spatter gel will help with this.

Flux Core Welding

Flux Core Welding produces better results

5. Flux Core Wire Sizes?

Same as in welding non galvanized steel.

You select the size of flux core wire to use according to the thickness of the metal you are welding, your welder and the welding Amp output of your welder. Unsure which size of flux core wire is best for your welder? Take a look at my article on the site here.

6. Weld strength Welding Galvanized Steel

The weld strength should be the same, whether welding galvanized steel or not. As long as the zinc oxide gets access to air to burn off. Welding thick galvanized coatings, or butt welds or welding creases or corners where the galvanization naturally builds up benefits from grinding the galvanization off first.

Remember for the zinc to be burnt off and turned to zinc oxide contact with air is needed.

7. What if the Galvanized Coating is Thin?

The thinner the better, less fumes to be concerned about. You may find you can do without a respirator as long as you position your head away from the fumes and you’re welding in a well ventilated area.

8. What do I mean by a well Ventilated Area?

Welding outside. You can’t get a more well ventilated area than that.

If you have to weld inside, weld in a large workshop where there a good through flow of air.

Small space?

Good airflow is crucial.

Air Flow from left to right or right to left, to take the plume of gasses away from you.

You could use a fan or an extractor to move the air if you’re in a small shed or workshop.

Do not use a fan behind you as your body will be blocking the air flow and never in front of you to blow the plume toward you.

9. What should I do if there is a thick Galvanized Coating?

If the metal is also thick then you may well find a spot of preparation makes things go quicker.

Use a grinder two inches either side of the weld point to grind off the galvanized coating ahead of welding.

You may find there are thicker area’s of galvanization, particularly when the steel has been hot dipped the galvanization can pool in the corners and creases.

For the zinc to be burnt off the heat of the flux core arc needs air to both burn off the zinc and for the flux to provide shielding for your weld. This is much more difficult in a corner or crease.

If this is where you are welding it may be easier to take a grinder to those areas first. To either reduce the amount of galvanization or open it up more to the air.

Remember to use protective glasses and a protective mask when grinding galvanized steel.

10. Cold Sanding of the Galvanized Coating

If you have decided to remove some of the galvanization with grinding remember that this too can send zinc oxide up into the air. Protect not only your eyes while grinding or sanding, wear a mask so as to not breathe in the dust.

Because zinc oxide dust is also produced through grinding.

11. Benefits of Welding Galvanized Steel with Flux Core Wire?

You can weld outdoors, which should solve the ventilation question.

It is the process of choice for welding galvanized steel.

I have a fuller explanation on the uses of flux core wire and welding galvanized steel is just one of them. Head over to my document on the subject for a complete 101.

12. Which Flux Core Wire to choose?

The considerations are the same whether welding galvanized or not. Choose the wire based on the capability of your welder and the wire properties.

Check the brand of flux core wire is suitable for welding galvanized steel.

Also that it is suitable for multiple passes if that is what you need to do for your weld

Choose the size of flux core wire to suit the thickness of the metal you are welding and the capabilities of your welder.

Flux core generally produces more spatter so look for flux core wires rated for low spatter to save yourself a lot of clean up. Or use Anti spatter spray on the surrounding area, (not on your weld joint) to protect your work piece. – link to anti spatter article

Some of my favorite flux core wires are;

13. YouTube Flux Core Welding Video

I found a useful video on YouTube that illustrates the flux core welding of galvanized steel. The video is about five and a half minutes long. The demonstrator doesn’t believe a MIG process – solid wire and shielding gas can weld galvanized, where as plenty of us do. Good preparation is needed as I describe above and yes flux core is the preferred method. It is none the less a very worth while video to watch.

GMAW vs FCAW when Welding Galvanized Material

Video Credit: weld.com

14. After Welding Galvanized Steel with Flux Core

Flux core welding generally doesn’t produce the prettiest of welds so you will need to clean all spatter, clean up your weld by grinding down or use a wire brush even if its only to remove the slag.

Cleaning up your weld and if you grind your steel in preparation for welding, will leave you with exposed steel.

That’s why once you have completed your weld you should reapply a protective coating.

As the metal was protected by galvanization it will most likely need re galvanization.

Spray with Forney Cold Galvanizing Compound Spray or

Rustoleum Galvanizing Spray

15. How Bad is welding Galvanized Metal for your Health?

Even when welding un-galvanized metal it is not a good idea to breathe in the plume from the weld. Good welder procedures should be practiced whether welding galvanized or not to prevent Metal Fume Fever or the zinc shakes.

Prevention is Best

Keep your helmet and head out of the rising smoke from the weld.

Do not breathe in the fumes.

Work in a well ventilated area – The advantage of flux core welding is that providing you can power your welder it is suited to welding outside.

Wear a respirator or mask suitable for protecting you from the zinc oxide under your welding helmet.

These are my favorite face masks to use.

White dust inside your welding helmet means you are not positioning your head properly.

16. Why Does Metal Fume Fever not affect some people?

Some people seem more tolerant to the zinc oxide fumes than others.

It is always best not to put yourself in direct contact with the gas plume that rises from the weld.

Fundamentally zinc is a necessary trace metal for all life on this planet and along with most good things in life, excess is never a good idea.

Over exposure by breathing in zinc oxide will make some people feel sick.

Metal Fume Fever

This sickness is called Metal Fume Fever or the zinc shakes.

How sick you feel depends on your susceptibility – essentially how allergic you are to zinc oxide and the level of exposure.

Some galvanizing processes use 100% zinc, however others, particularly old galvanizing have small amounts of lead in them. Lead oxide should never be breathed in.

Symptoms

Feeling like you have the flu. Shaking, nausea, headache, feeling really tired and joint pain are all possible symptoms. Along with a dry throat or tickly cough, a sweet or metallic taste in the mouth.

Most effects disappear within twenty four to forty eight hours. Though full recovery could take up to three weeks.

And it is possible to build up a level of tolerance if you are welding galvanized metal daily. The tolerance doesn’t last long unfortunately. Away from the welding for a couple of days then weld galvanized and the symptoms can come back. This was also why it was called Monday Morning disease!

Treatment

Rest, drink plenty of water, take an over the counter painkiller for your headache and joint aches and pains

Some swear by drinking a glass of milk before or immediately after welding galvanized steel. For some it works.

But there is little scientific evidence to support it. If you are lactose intolerant then this isn’t going to be the option you would choose.

Prevention is better

Conclusion

There you have it, the 16 things to know when flux core welding galvanized steel. With this knowledge you should be happily and safely welding your galvanized projects in no time.

 

Additional Reading Resources

American Galvanizers Association

Welding After Galvanisation

Article Welding Galvanized Steel Safely. Parts of this article appeared in the Fabricator