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The Enemy: Rust The Answer: Zinc
Oxygen and moisture working on iron and its common alloy, steel, result in rust. When thinking in terms of the wire used for fencing, sometimes being number one is not always tops. A Class 1 coating for your mesh or fence is anything but top rate. Now think again about that coating. It can mean: this looks fine or it'll do. In the long run (or short run), it will not stand up to the ravages of air, moisture, and abrasion.
However, a coating of zinc reacts differently to these factors. As it corrodes. It forms a barrier or patina, running interference between it and the steel or iron that it is sheltering.
The Protector: Zinc
Classes of Zinc Coating
Class 1--lightest coating of zinc; widely available and lasts 2 to 11 years in non-coastal climates. (.28% zinc per sq. foot)
- protection drastically reduced in humid climates. (For the record, there is no Class 2.)
Class 3--heaviest coating of zinc; lasts 13-30 years, often must be special ordered (.80% zinc per sq. foot)
- however, in humid conditions, the coating may last at least 15 years with wider wire gauges lasting longer.
Zinc galvanization--a coating for mesh and fencing that endures.
After wires are either welded or woven into a mesh, the entire finished product is drawn through a bath of molten zinc (830°F.) This galvanization-after-weave or weld method (GAW) creates mesh that emerges with a thick coating tightly bonded to the wire. Each strand of wire is protected and more importantly, each vulnerable welded or woven area is thoroughly sealed. In some circles, this is known as "galvanic healing!" Officially, this is termed, cathode-anode protection.
More zinc = more protection. Delaying the time until rust sets in.
So the more zinc per square foot, the longer it is until it rusts.
If something is friable, it is subject to the rubbing process that works on the surface of unprotected iron or steel, which offer no natural corrosion resistant patina. Friability describes the flaking and breaking apart of a solid substance.
Simply put, what are the benefits of a Class 3 zinc coating?
- Lowest cost over the long run
- damage resistance--the zinc patina guards the metal underneath
- cheaper than stainless steel
- consistent results
- longest life
What does an ASTM standard signify?
Seeing this on a product, such as for zinc coatings, shows that a company is adhering to a certain set of criteria for the quality of a product. These are internationally accepted guidelines, based on research, for the specifications of materials, products, and services as approved by a governing board. (ASTM International was once known as the American Society for Testing and Materials.) Buyer beware: a company's adherence to these standards is voluntary.
Other factors for deterioration:
airborne sand and dust chemicals salt air pollution
Zinc facts:
Zinc is the 27th most abundant element in the earth's crust. 70% is mined, 30% recycled. More than 50% of this is used to coat steel and keep it from disintegrating.
Zinc is found in rocks, soil, air, water, the biosphere as well as in humans, plants, and animals.
Biology: organisms must have zinc to exist. For example, in the human body, zinc is important for cell division and is responsible for the function of red and white blood cells.
Here's an example of zinc galvanizing in action:
