Posted on: 13 May 2015Share
Wrought iron work fences are beautiful and strong, but they have one significant disadvantage when compare to aluminum fencing: most wrought iron rusts if it's not routinely maintained. A hot-galvanized wrought iron fence, however, will last for decades without rusting. If you're installing a wrought iron fence around your home, talk to your contractor about hot-galvanized wrought iron. It may cost a little more than a zinc-plated wrought iron fence, but hot galvanization will make your wrought iron fence just as impervious to rust as aluminum is.
Iron Rusts When Left Exposed to the Elements
All iron, including wrought iron, is susceptible to corrosion when it's left outdoors and exposed to the elements. As Fred Sense of Frostburg State University explains through chemical equations, when iron (Fe) comes into contact with water (H2O), the compounds undergo a series of reactions that eventually produces iron III hydroxides (Fe(OH)3). This is a wet compound, but, when it dries, it forms iron III oxide (Fe2O3), which is more commonly known as rust.
In short, the iron compounds in wrought iron interact with the oxygen found in water to form rust. Certain conditions, such as smog or acid rain, speed the rate of corrosion up, but there also are ways of delaying, or even preventing it, namely through galvanization.
Galvanization Prevents Rust with Zinc
Galvanization is the process of coating an iron (or steel, which contains iron) object with zinc. The zinc, which does not react with oxygen, forms a film between the iron and oxygen molecules. Since they don't come into contact with each other, they don't react. Thus, the thin layer of zinc prevents the iron from corroding.
The effectiveness of galvanization depends directly on how well zinc is applied to the iron. If it's not evenly applied, it will not provide equal protection. Even worse, if some iron is left exposed to oxygen, those areas may quickly rust.
When purchasing a galvanized wrought iron fence, therefore, it's important to make sure the zinc was evenly applied to all parts of the fence.
Hot Galvanization Provides More Protection than Cold Galvanization
There are two types of galvanization: hot and cold. Although it's a much more involved process, hot galvanization is more effective than cold because it evenly coats all parts of the wrought iron fence with zinc. Cold doesn't.
In hot galvanization, a wrought iron fence is dipped into a molten zinc bath. Leading up to this final stage, the iron is dipped into several other baths, as Voigt & Schweitzer shows. Before actually being dipped into the zinc bath, the iron goes through:
- a caustic cleaning
- a pickling stage
- a flux solution
- two rinses
Because the wrought iron pieces are individually dipped into the zinc bath during hot galvanization, all parts of the fence are evenly coated with zinc. Even the insides of hollow posts are coated with zinc and protected from rust.
Cold galvanization, in contrast, protects the iron by applying a zinc-laden paint at room temperature. Many companies use cold-galvanized wrought iron, because it's a simpler process than hot galvanization. The paint, which is often stored in a spray can, can be sprayed on in a factory or on-site.
Since the zinc is painted on, cold galvanization doesn't afford the same equal application as hot galvanization does. Also, the inside of a fence post can't be coated using this method, which leaves wrought iron fences susceptible to rusting from the inside-out. No matter how carefully the zinc is painted on, it's impossible to achieve the same level of protection using cold galvanization as hot galvanization provides.
Hot-Galvanized Wrought Iron Fences are Strong, Beautiful and Last
If you're looking for a strong, historic-looking fence that will require little maintenance, consider installing a hot-galvanized wrought iron fence. Most iron fences will rust outside, but wrought iron that's been hot galvanized will last for decades without needing any attention. In fact, a report published in Fastener Technology International found that they'll last for 50 to 80 years. By the time your fence needs some attention, it'll be someone else's responsibility to take care of it.