Manufacturers typically provide a 25-plus year lifespan estimate. While such claims are not completely falsified, they only reflect optimism under specific, rare conditions. There are plenty of external conditions beyond the manufacturers’ control that negatively impact a fence. For the consumer’s benefit, time estimates on lifespan are not guarantees. It’s more useful to assess fence characteristics that contribute to a shorter or longer fence lifespan.
Galvanised vs Powder Coated
It is common to academia that Galvanising and Powder Coating are the two major types of fence protective coatings. The ideal fencing would use an combination of both protective coatings.
Galvanising or Galvanization is a de-facto industry standard term that is synonymous with corrosion protection. The major difference in the two methods of Galvanization is that Hot-Dipped Galvanization is the immersion of fabricated steel in a pot of nearly molten zinc, around 450°C. It is refortified to a zinc to steel protective coating and adds around 45-85 microns of thickness. This in turn provides the steel some corrosion forgiveness. If a Hot-Dipped Galvanized steel fence is fully unpainted, an unprotected steel fence, the fence will withstand corrosion for around 20-40 years.
A powder coating provides an attractive extra layer over galvanizing to provide extra moisture (like water from rain) or UV (from the sun) to protect the metal. It is attractive to look at and can improve the lifespan of a metal fence. However, over time, if there is a minor breach to the powder coating (like scratches from a lawnmower or holes from new fixings), the fence will develop rust. In the UK, a powder coating will most likely breach. However, the likely breach may be smaller over time and may not be large scratches like holes from new festings, even though it is likely not as attractive after a breach. For long-lasting fencing, hot-dip galvanzing with powder coating is recommended over spray galvanizing (also known as cold galvanizing), which is a cheaper method. However, spray galvanizing is not as effective as hot-dip seeing as galling is only painted to the surface, rather than painted, bonded and, importantly (sacrificial) protective, to the surface like hot-dip. Powder coating is only recommended for fencing that is to last 20 years.
Aluminium Is Not Premium — It’s Just Different
The market for fencing councils aluminium as a premium fencing option. In reality, aluminium and steel offer very different things. Unlike steel, aluminium doesn’t rust. Aluminium’s reaction to oxygen in the air forms a protective layer that stops the corrosion from happening. For that reason, a powder coated aluminium fence will not rust like steel will with a compromised coat. Steel will rust and oxidize because it contains iron.
But, aluminium does offer something in return — it will not be as strong. Steel is typically stiffer and harder to break or form. In instances like a fencing boundary application that would be subject to something that would be hitting the fencing like a vehicle or a person leaning on it, or something like equipment, steel will go through much less deformation and bend much less than aluminium will, and aluminium is not like steel as it will not go back to it’s form, bend, and be the same without a noticeable difference.
Practical implications of this mean aluminium fencing is a good option in places, very corrosion-prone places, that have a very low risk of impact. Places like the coast, or places with lots of moisture in the air, or places that have a very low wish to have to maintain the paint on it are all good places to use aluminium fencing. Places where steel will actually be worth it are places like the edges of something where vehicles are driven like a driveway, or places where lots of equipment are kept and are very close to the fencing.
The Reality of UK Weather Related to Metal Fencing
The factors that lead to corrosion of metal fencing in the UK are moisture, salt, and the level of industrial pollution. Metal fencing in coastal places is potentially quite problematic, especially within a distance of say, 2 to 3 miles from the sea. The air in these places carries a high amount of salt which substantially increases the rate of corrosion of ferrous metals. A galvanising that would last 30 years in the interior of the country may last only 15 to 20 years along the coast, meaning, the surface inspection interval should be less than it would be prescribed to be in an internal land.
Environments that are urban pose a different danger. The presence of sulphur dioxide in the air combined with the oxides of nitrogen emitted by the vehicles react with the water to form mild acids that precipitate on metal surfaces. Corrosion of metal surfaces in urban areas may be less than that of coastal areas, corrosion in urban areas is sustained over a long time and will still correlated corrosion of metal surfaces. Corrosion in urban areas will be especially problematic for metal surfaces that are horizontal on which water will puddle for extended periods of time.
Outside of coastal rural areas is to be corrosion of metal surfaces is to be the least risk. That is not to say that such areas pose no risk. However, rural agricultural areas do have risk. Typically in order to irrigate the agricultural areas a lot of soil and a lot of fertilizer is pumped into and around the agricultural area causing a significant amount of corrosion spolis to be present in the air. A combination of soil moisture and corrosion spolis of the air may be very problematic for metal surfaces of fencing that are not protected.
Thus, when prescribing appropriate inspection and maintenance intervals for metal fencing corrosion, the environment, and especially the level of exposure to salt, moisture and industrial pollution must be taken into consideration. The information provided in various brochures on metal fencing do not tell the whole story in terms of the rate of corrosion of metal fencing.
Why Life Span Predictions are Incorrect
This figure of twenty-five years assumes correct fencing installation. One way fencing fails is by using post foundations. They are almost completely obscured, and are completely failing until it becomes evident, of which corroded steel posts at the bottom are the most evident. If the bottom of the steel post is in the ground, it is likely not coated at all, and is likely not painted, and it is at the post and the fence position where most fencing becomes dysfunctional.
Concrete collars that sit exactly at the same level as the concrete posts are worse than collars that direct water, i.e. in the envelopes, away from the joint. Avoiding water collection in the hollow at the post top by providing water-proof caps is not all that complicated, and it will improve the entire post top. This is not by any means complicated, and it differentiates fencing that will end up like Post and Wire, and require fencing that will end up in the post beside the wire, falling apart.
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