Welding galvanized steel is a classic example of a situation in which two metals with extremely different properties have to be reconciled in a single joint. Zinc vaporizes at a temperature at which steel is only just beginning to soften, and all the typical problems stem from this one difference – from weld porosity, through an unstable arc, to toxic zinc oxide fumes. How do you overcome these difficulties and make a durable, well-protected joint?
Can galvanized steel be welded?
Yes – galvanized steel is ordinary steel covered with a layer of zinc, so it can be joined using the same methods as black steel. This will only work, however, under certain additional conditions: you must remove the zinc coating from the weld zone and ensure effective ventilation. Skipping either of these steps leads to a defective weld and a real health hazard for the welder.
Why is welding galvanized steel more difficult?
The core of the problem is the temperature difference between zinc and steel. Zinc melts at only approx. 419°C and vaporizes at approx. 907°C, whereas steel does not melt until around 1500°C. This means that in the welding arc, zinc boils violently and vaporizes before the base material has even had time to melt.
The effects of this phenomenon are above all:
- Weld porosity – zinc vapors trapped in the solidifying weld pool form gas bubbles that weaken the joint.
- Unstable arc and spatter – vaporizing zinc disturbs the arc and worsens the appearance of the weld face.
- Toxic fumes – vaporized zinc oxidizes in the air to zinc oxide (ZnO), forming a characteristic white-greenish smoke.
That is exactly why zinc is removed from the welding zone instead of being "burned through" by the arc.
Zinc fumes – occupational health and safety hazards when welding galvanized steel
Inhaling zinc oxide fumes causes metal fume fever (also called zinc fever or foundry fever). It is a respiratory illness typical of welders, producing a flu-like set of symptoms: chills, fever, muscle and head aches and a metallic taste in the mouth. Symptoms usually appear several hours after exposure and subside on their own within 24–48 hours, but with repeated exposure they become a recurring complaint.
The basic means of limiting the concentration of harmful fumes at the welder's station is mechanical ventilation. In practice this means:
- working with local exhaust (a nozzle guided behind the torch) or in a well-ventilated room;
- using a half-mask with a particulate filter and, in worse conditions, a powered air-supplied respirator;
- for occasional work outdoors – positioning yourself so that the smoke is carried away from your airways.
How to weld galvanized steel step by step
The process itself does not differ drastically from welding black steel, but two additional stages are added to it: surface preparation and restoring corrosion protection.
Surface preparation – removing zinc from the weld zone
The zinc coating should be ground off over a strip approx. 1–2 cm wide on both sides of the future weld, until clean, bare steel is exposed. An angle grinder with a flap disc or a wire brush works best. After grinding, it is worth degreasing and drying the surface. The more thoroughly you remove the zinc, the lower the risk of porosity and the more stable the arc.
Welding galvanized steel with an electrode (MMA)
Welding galvanized steel with a coated electrode is a method readily chosen in the workshop and in the field, because it does not require shielding gas and tolerates field conditions well.
- Use rutile or basic electrodes suitable for the steel grade.
- Keep a short arc and a slightly slower travel speed to give the zinc vapors time to escape from the pool.
- With thicker elements, a light weaving motion that "degasses" the weld can be helpful.
- Remove slag thoroughly between passes.
Welding galvanized sheet with the MIG/MAG method
Welding galvanized sheet with the MIG/MAG method is the most popular for thinner sections, because it offers high productivity and a nice weld face. Recommendations in this case include:
- solid wire (e.g., G3Si1) or flux-cored wire, shielding gas containing CO₂ (Ar/CO₂ mixtures);
- the "drag" technique, pulling the torch away from the weld (this moves the smoke away from the pool and improves fusion);
- slightly higher voltage and controlled wire feed (to limit spatter);
- for thin sheet, intermittent welding (tack welds) so as not to burn through the material.
| Method | Typical application | Key rule |
| MMA (electrode) | Workshop, field work, thicker elements | Short arc, slower travel speed |
| MIG/MAG | Thin and medium sheet, series production | Drag technique, spatter control |
How to restore the zinc coating after welding
A weld stripped of zinc is the weakest corrosion point of the entire structure – the exposed steel begins to rust exactly where the coating was removed and vaporized. That is why the zinc coating has to be restored after welding. In accordance with the EN ISO 1461 standard, three repair methods are used:
- Zinc paints and pastes – applied by brush or spray, the most convenient on a construction site; they should contain a high proportion of zinc (on the order of 80% or more in the dry coating).
- Thermal spray metallizing (thermal spraying of zinc per ISO 2063) – durable, but economical mainly in factory conditions,
- Zinc sticks with a low melting point – for minor touch-ups on horizontal surfaces.
Industry guidelines (including those of the Galvanizers Association, a member of EGGA) indicate that the restored coating should have a thickness of at least 100 µm, and the total repair area should not exceed 0.5% of the surface of the element – with larger losses, the element is sent for re-galvanizing.
Weld before or after galvanizing – which pays off more?
In most steel structures, it is most advantageous to weld the entire element first and only then galvanize it as a whole. This approach has an advantage over welding finished, galvanized sections:
- welds are covered with zinc together with the rest of the structure, so no unprotected "weak points" are created;
- the coating is uniform and continuous, including in crevices and inside closed profiles;
- labor-intensive zinc removal, fume extraction and manual restoration of protection are no longer needed.
For load-bearing structures and elements used outdoors, the standard is hot-dip galvanizing of the finished structure, which by immersion also covers all welds. You can do this at Strumet – we run the largest hot-dip galvanizing plant in the Podbeskidzie region. A coating applied by immersion covers the structure completely, and its durability averages 30 years.
FAQ – the most common questions about welding galvanized steel
Can galvanized steel be welded?
Yes. Galvanized steel is steel with a zinc coating, so it is welded using standard methods, provided the zinc is removed from the weld zone and ventilation is ensured.
What should galvanized steel be welded with?
Most often with a coated electrode (MMA) or the MIG/MAG method. The choice of method depends on the thickness of the material and the working conditions – in the field MMA wins, on thin sheet MIG/MAG.
How to weld galvanized steel with a MIG/MAG welder?
Grind off the zinc, guide the torch using the drag technique (away from the weld) and control the parameters to limit spatter. With thin sheet, weld intermittently so as not to burn through the material.
How to weld galvanized steel with an electrode?
After removing the zinc, weld with a short arc and a slightly slower travel speed, giving the zinc vapors time to escape from the pool. Remove slag thoroughly between passes.
How to protect a weld after welding galvanized sheet?
Restore the zinc coating with a zinc-rich paint or paste or with thermal spraying, achieving a thickness of at least 100 µm. An unprotected weld quickly begins to corrode.
