5 Common Questions About Galvanized Steel
How long will my zinc coating last?
The lifespan of your zinc coating will depend on a number of things including coating weight, environmental conditions and whether you need the zinc to aesthetically look pleasing throughout its use.
On average, Galvinfo says you can expect a 1-mil thick coating to last for 30 years in a rural environment, and a 2-mil thick coating to last for about 70 years before it starts rusting.
However, these numbers swing widely based on corrosion rates in specific environments. For example, if the air is humid and the steel is constantly wet, corrosion will take place at a much faster rate, even if the pieces of steel are identical.
What coating weight do I need?
Again, this will depend on where you’re using it and the rate of corrosion in that environment. Typically indoor HVAC ductwork performs well at a lower coating weight, whereas something like a highway guard rail would require a thicker coating weight.
One thing to remember is that thicker isn’t always better. Because zinc coatings corrode slowly, you should try to identify the proper coating weight for your end use. Otherwise, you could end up over-paying for something that’s unnecessary. Learn how to choose the right coating thickness here.
How exact is the coating thickness?
In the past, coating thickness was a tricky beast and could be difficult to gauge correctly. As technology has advanced, however, so to has our ability to properly apply coatings to substrate. And even though modern coating lines are able to control thickness incredibly well, all gauge charts still list a minimum and a maximum coating thickness for each gauge.
For example, 24-gauge must fall between .0236 and .0316. If the thickness falls outside of those ranges, the material cannot be sold as 24-gauge. Keep the ranges handy, and download your own printable gauge chart here.
Why would I need a coating other than zinc?
Sometimes zinc alone isn’t enough. In the case of Galvalume steel, aluminum is added to the equation for superior corrosion protection. Often, Galvalume is used on roofs, where additional corrosion resistance is needed.
In another example, if your end use requires resistance to high heat, you may add aluminum and silicon to the bath. You’ll find that this kind of aluminized steel is often used in heat exchangers for residential furnaces and commercial HVAC units.
How can I test coating thickness?
While there are four ways to measure thickness, the easiest and most non-destructive method is by using a magnetic thickness gauge. Today, many people use an electronic tester, though mechanical gauges are also still common. They’re also more cost effective – around $350 versus $600 for an electronic gauge.
So, what’s the benefit? Electronic gauges are more accurate, within +/- 1% accuracy, where dial-type micrometers are within +/- 5% accuracy. They’re also easier to read because they provide a digital display.
Regardless, once you’re trained on either a mechanical or digital reader, both provide a fast and reliable way of testing for thickness.