While metals like iron and steel offer various advantages, one of the biggest issues with them is oxidation.
This is the process in which oxygen in the atmosphere reacts to the iron components of the metal and starts the rusting process.
To combat the corrosion, the surface of the metal can be coated with a protective layer like hot-dip galvanizing.
Unpainted galvanized metal can however get weathered and rust with time if exposed to the atmosphere, especially during highly humid or cold conditions.
This is due to the fact that protective zinc coating will oxidize with time making the galvanization coating ineffective.
So, is it OK for you to paint over galvanized steel?
Painting hot-dip galvanized steel (also known as a duplex system), is important for better durability, especially if the surface is exposed to the environment.
But because painting galvanized steel is not a straightforward process, you’ll need to apply the right kind of paint very carefully so that it won’t peel off or shed fast.
Below in this article, we will get into some details on how you can successfully paint over hot-dipped galvanized steel and what things you need to consider while performing the job.
Let’s start with some basics first…
What is Hot Dip Galvanizing?
Hot Dip Galvanization is the immersion of metal, normally steel or iron, into molten zinc.
The zinc will alloy with the surface of the metal to create a protective layer.
The oxygen in the atmosphere will react to the zinc which crates zinc oxide.
And since zinc oxide resists corrosion, which acts as excellent protection for metal surfaces.
- Much durable with high coating strength
- Highly resistant to environmental impacts
- High maximum operating temperature – up to 665ºС
- Double corrosion protection with a warranty period of up to 75 years
- High costs involved
- Complex technological process
- Can develop white rust over time
- Cannot be done manually – only industrial
- Challenging to repair the damaged coating in future
How to Paint Over Galvanized Steel?
If you’ve ever tried to paint hot-dipped galvanized steel or other metal surfaces, you already know how hard it is for the paint to adhere well to the surface.
The metal surface generally rejects the paint because of the layer of zinc (left after the galvanization process).
This is the layer that is responsible to reduce corrosion and due to this protective layer, the paint gets peeled fast.
To overcome this problem, you can follow a step-by-step process which makes adding a coat of paint to galvanized steel simple.
Step 1. Clean the surface
Applying a coat of paint to a dirty surface doesn’t make any sense.
So you will need to clean up all the dust, dirt, or other grime buildups before you paint over the galvanized metal surface.
To clean galvanized steel before painting, rinse with warm or hot soapy water and then allow it to dry completely.
Step 2. Apply vinegar and primer
White vinegar (found in your kitchen) is an effective non-toxic solution that can react with the metals like steel.
Also, because of its acidity, vinegar can treat the surface to promote paint adhesion.
So, you can simply wipe down the galvanized surface with a clean rag before you apply primer and paint.
After applying the vinegar it’s good to prime the surface with a metal primer (although it’s optional).
Step 3. Apply the right paint
After you have prepared the surface, it’s time to paint the smooth galvanized steel surface.
Rust-oleum paint for spraying weathered galvanized metal works great for most surfaces.
These paints adhere better and will require less prepping work compared to other paint types.
Many people prefer using acrylic latex paint or even epoxy coating.
IMO, these are not designed specifically for galvanized steel so if you opt for them you will need to prime the surface first before painting.
Alkyd-based paints and oil-based primers are also not meant for galvanized steel so you should avoid using them.
Tips and Considerations
The above method to paint over galvanized steel is effective and useful when you are coating the surfaces at home.
However, for industrial purposes (such as automotive, construction, telecommunication, etc.) extensive cleaning and roughening of the surface is important.
Sweep blast cleaning (also known as abrasive brush-off blast cleaning or sweep blasting) is a technique that is often used for this purpose.
Sweep blasting is a type of abrasive blast cleaning technique that loosens debris and roughens the galvanized surface of a substrate before painting or coating it.
Sweep blast cleaning is named so because here the abrasive blasting is done with a fast pass or light sweeping technique.
Sweep blast cleaning should be aggressive enough for cleaning and in the process, the light sweeping action is primarily used to improve the adhesion of the topcoat intended to be put over the galvanized surface.
Can Powder Coating Be Applied to Galvanized Steel?
Yes, you can apply a powder coating to galvanized steel to offer greater protection.
The coating can be applied using the same techniques as metal that has not been galvanized.
The result is that the object has enhanced corrosion protection since it must get through the powder coating first and then the zinc oxide which has been galvanized to the surface.
The combination of powder coating and hot-dip galvanizing is arguably not as frequent as the use of just one method.
But it is well-suited for metal objects (made of iron, steel, aluminum, etc) that are exposed to the elements and yet not touched all that often.
An iron fence would be a good example as opposed to an iron gate that allows for people to pass through.
Powder Coating vs. Hot Dip Galvanizing – Which One is Better?
The answer depends on the situation.
For metal items that are outside, the galvanizing process is clearly the best.
This normally means gates, fences, and guardrails that are made from iron and steel.
Powder coating is generally better for decorative objects, especially those that are indoors.
Or, items that would not survive the galvanizing process.
There are ways to bolster the powder coating to make it more resilient.
However, it is more subject to removal by friction, so it is not as well suited to surfaces that come into frequent contacts such as handrails and the like.
So, while hot-dip galvanizing offers stronger protection for longer periods, it is also more expensive and not needed for many applications, especially decorative items that are indoors.
Also keep in mind that both these coatings are not meant for surfaces made of rubber, plastic, wood, or anything else that can melt/damage at high temperatures.
What is galvanized steel used for?
Galvanized steel is highly versatile and is majorly used in home construction to make corrosion-resistant nuts, bolts, nails, outdoor pipes, staircases, walkways, benches, ladders, and much more.
In addition to usage in schools and hospitals, hot-dipped galvanized steel is also becoming a go-to material in the auto industry for making cars, vans, trucks, motorhomes, and RVs.
The truth is that the technology for making environmentally-friendly galvanized steel products is constantly evolving and the material is therefore finding its way into various other industries rapidly.
Can galvanized steel be painted?
No, the fact is, that the paint will not adhere very well to galvanized steel materials.
The layer of zinc that is applied during the galvanization process reduces corrosion. But at the same time, it will also reject the paint layer.
The result is, if applied without proper preparation, the paint will eventually peel or shed.
Is galvanized steel stronger than black steel?
Steel is already an extremely durable material. And when galvanized, the protective zinc coating will make it even better.
Black iron pipes or black steel pipes, on the other hand, are uncoated and are relatively less durable.
This means water and other environmental elements can corrode this type of material fairly easily.
The Bottom Line
While both (galvanized and powder coating) protect the surfaces of metals like steel pipes, the big difference is how they do so.
The powder coating resists the elements that cause corrosion while galvanizing absorbs the corrosive materials before it reaches the surface.
The differences may seem subtle, but they are important because, in situations where the metal is continually exposed to moisture, the galvanizing process works better.
Even better if you use the right tools, and follow the process to paint over these galvanized metal surfaces, you will be enhancing the life of your project many times.
Jack Luis is a semi-retired painter who loved painting his clients’ ideas on their walls.
He had worked as a painter for over a decade serving customers in areas such as Charleston, Mount Pleasant, Beaufort, and Georgetown, SC (South Carolina). Today in his free time, he likes to read and write about the newer techniques implemented in his profession. You may read more about him here or get in touch with him here.