How to Paint Over Hot-dipped Galvanized Steel?

how to paint galvanized steel

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.

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.


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 an excellent protection for the metal surfaces.

PROS:

  • 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

CONS:

  • 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.

Step 2. Apply the vinegar

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 paint over. 

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. 


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.

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 that 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.

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