The term coating weight refers to the amount of zinc applied to a product for a given surface area. Two different methods can be used to measure the coating weight of hot-dip galvanized steel.
The first method to measure the coating weight involves using a process called weigh-galvanize-weigh, and is only appropriate for single specimen samples. The zinc coating weight from this technique is underestimated because the actual coating is made up of both iron and zinc and this method will only measure the added zinc weight in the coating. In addition, it can be very difficult to measure and calculate the surface area of a complex steel fabrication, and this makes coating weight values even less accurate.
Weigh-strip-weigh is the second method used to measure coating weight, and again is only appropriate for single specimen samples. This method is destructive since it removes the hot-dip galvanized coating during the measurement. This process involves first weighing the specimen, stripping it of all zinc coating that was added, and then weighing it again. The difference in the weights is then equal to the amount of coating added during the galvanizing process. However, this method is usually only used on very small products like nails, and can be inaccurate because when the coating is stripped there may be some base metal stripped along with the coating. This means that there may be extra iron included in the weight measurement, making for a higher than actual zinc coating weight.