Steel has long been known as one of the most durable building materials out there. For frameworks where great strength is required, there’s no competitor. But for outdoor, exposed applications, even steel needs added protection. Various coatings and finishes are available, but one of the most common is galvanizing. Galvanized steel has either been dipped in or electroplated zinc as a rust-resistant treatment, enabling it to withstand even extreme weather exposure. The zinc, when exposed to weather, corrodes so that the steel underneath does not. So, if your welding work involves steel that will be used outdoors in various weather conditions, or even indoors but requiring additional durability, you’re likely to work with galvanized steel.
Welding Galvanized Steel
Properties of Zinc
For a successful steel weld, working temperatures need to exceed the melting point of steel (2750°F). Zinc, however, melts well below that temperature—at about 900°F—and vaporizes around 1100°F below steel’s melting point. So, in the process of welding steel, zinc is obliterated, and the outcomes can vary depending on the method of galvanizing used on the steel piece(s).
Electroplated vs. Hot Dipped Galvanized Steel
The coating methods for galvanized steel are chosen for different applications. When thicker coatings are acceptable, the hot dipped method is employed. For thinner coatings (often in the automotive or aeronautics industries), electroplating is used.
During welding, the zinc coating burns off hot dipped steel, and the result can be a “dirty” weld. Electroplated materials (with a thinner coating) will usually produce a cleaner weld with less of the zinc material burning off. For best results, prepare the areas to be joined by grinding the coating so a smoother weld can be achieved.
Potential Health Dangers of Zinc Fumes
Vaporized zinc mixes with oxygen in the air and produces zinc oxide. Long used in cosmetics (and for sun protection), zinc oxide is technically considered “safe” (as in, not toxic or cancer-causing). However, inhaling it can produce flu-like symptoms that will make a welder quite miserable. So even if it isn’t considered unsafe (though some would disagree), the resulting exposure ailments mean it’s wise to prepare your work area properly so that you can avoid exposure and filter zinc fumes so you don’t breathe them in.
Begin by always positioning yourself out of the fume plume and so that air flows around you, preventing dust and fume buildup in your welding hood. A respirator mask will add extra protection. Half masks, similar to painter’s masks, are inexpensive and will do the trick. They’re easy to add to your workflow and aren’t bulky under your welding hood. For higher cost, masks with activated charcoal will also filter the zinc oxide fumes while reducing other work area odors. These masks can make your experience with galvanized or any materials much more comfortable.
In addition to protecting yourself from exposure, your newly welded (zinc-free) joint should be protected with a zinc-rich primer to reduce corrosion.
In many ways, welding with galvanized steel is similar to any other steel welding job (simply because once you get to the steel, there’s no zinc remaining in the joint). But because zinc burns off and produces zinc oxide fumes that can make you feel very ill, preparation and caution are important. Finally, after the weld has been completed, any exposed steel must be treated so that the joint is weather resistant like the remaining galvanized steel, or you’ll lose the benefit of working with such a material.