【Haichuan Anti-corrosion Knowledge】If it’s already galvanized, why is painting still necessary?

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Have you also asked yourself this question in your heart? A phrase often heard from customers is: “It’s already hot-dip galvanized, so why apply paint?” It’s unnecessary. ” It’s not only amateurs who say this; many experienced workers in the construction industry think the same way. It sounds pretty reasonable – galvanizing is meant for corrosion protection, so applying another layer of paint is just wasting money So when this idea came to mind, I started to be frugal: cut as much as possible, and avoid doing things if it wasn’t necessary. So what was the result? The problem isn’t revealed on the same day; it emerges slowly over three to five years, and by then it’s too late to regret it. Is galvanizing a solution that lasts forever? Galvanizing is indeed reliable, and many people consider it to be the ultimate solution that solves all problems, but that’s not the case. The essence of galvanizing is to let zinc take the brunt on behalf of the steel. It acts like a shield of sacrifice, standing in front and gradually being consumed by the environment; the key lies in this process of being gradually consumed. In coastal areas, industrial zones, and places with heavy acid rain, zinc is worn away very rapidly. What’s worse is the actual situation on site: welding generates heat, cutting involves sharp tools, and handling during transportation inevitably leads to impacts; in such places, the zinc coating is already damaged, and corrosion starts to penetrate through these small cracks and spreads gradually outward. It may look bright on the surface, but it could already be rotting inside. Why do many projects require an additional coat of paint? It’s not to add an extra buff, but rather for everyone to do their own job with clear division of tasks. The internal strength of galvanized pipes – prevents the steel itself from rusting easily. External function of paint tubes – to keep out harmful substances such as water, air, salt spray, and acid rain. One carries it at the front, while the other guards it from the outside; combining these two actions yields an effect that’s not as simple as 1+1 – it can be several times greater. For many projects, the use of a combination of galvanizing and painting allows for a service life that is 10–20 years longer, or even more, compared to those with only galvanizing. For those projects with strict requirements regarding service life, such as municipal projects, power transmission towers, offshore platforms, and chemical plants, almost no one dares to rely solely on galvanizing. It has been treated with preservatives – why are there still problems? For some projects, the paint was applied and all the necessary procedures were followed, but in the end there was still significant peeling, bulging, and flaking. There’s only one reason: doing something doesn’t mean doing it right. The most common mistake is applying ordinary paint directly to galvanized parts. It just got painted; the color is nice and the surface is smooth. When the client inspected it, they praised the quality of the work. But after a year or two, it starts to fall off when tapped, piece by piece, like wall paper. Many people’s first reaction is that it’s the paint that’s the problem, but in most cases it’s not necessarily the paint at all; rather, it’s simply not sticking properly. A galvanized surface is smooth and shiny; however, it comes out of the factory with a passivation layer and oil residues on it. If you paint it without doing anything to remove those residues, the paint will behave like plastic touching glass – how can it adhere properly? There’s even worse: the surface treatment is completely skipped, or it’s just wiped down a bit and polished before painting. As a result, there’s no need to wait three years; the consequences will be shown to you right there on the spot. What is the most easily overlooked fundamental aspect? Everyone focuses a lot on \"what kind of paint to use\", but what is often overlooked is the previous step – surface treatment. In the article titled “Failing to do this step before painting means that paint peeling will only be the beginning,” I explained in detail just how important surface preparation is – tasks such as degreasing, sanding, and gritting may seem trivial, but they are actually key to determining whether the paint will hold up over time. Reading link: If this step isn’t done properly before painting, paint chipping will be an inevitable consequence. Failing to remove oil, skipping sanding, or not using proper sanding techniques – all of these will render even the most expensive paints and top-notch teams useless. It’s easy to talk about, but it’s the easiest thing to overlook when it comes to actually doing it. It’s invisible, intangible, and not easy to inspect, but it is the key factor that determines whether the anti-corrosion measures will be effective. Should paint be applied on top of the galvanized layer? It can be determined in just three sentences. I don’t use complicated criteria to deceive people; instead, I ask myself three simple questions: How many years is this thing supposed to be used? Is the environment highly corrosive? (Coastal areas, chemical industrial parks, and areas affected by acid rain are all considered to have high corrosivity.) If problems arise in the future, will it be easy to repair or replace them? If it’s a temporary structure, the environment is decent, and it can be repaired easily if it breaks down, then plain galvanizing is indeed sufficient and saves money. But whenever it is used for a long time, in a poor environment, and requires costly and complicated maintenance, the money saved on paint costs now will most likely have to be repaid in double, or even several times more, later on. Saving money in the short term means incurring losses later on. Many people think that applying one less coat of paint means saving money. But the most common scenario is that the small amount of money saved today has to be repaid years later with much greater trouble – rework, production stops, and even safety hazards. Sometimes it’s not that preservation isn’t carried out, but rather — the wrong method is used. In reality, the more painful question isn’t whether to scroll or not, but rather: if one does scroll, why still fail? Especially with galvanized parts, it’s only at the end of many projects that it becomes apparent – paint has been applied, but it hasn’t stuck at all. In your projects, have you encountered situations where paint peeled off in large areas after galvanizing? Feel free to share your experiences in the comments section; I’ll go over in detail the most common mistakes that people make on site.