How to paint and seal HDG steel

If you’ve ever tried to paint over hot-dip galvanised (HDG) steel and found the paint peeling or flaking off a few months later, you’re not alone. Painting galvanised steel can be tricky if you don’t prepare it properly. But don’t worry, with the right know-how, it’s doable.

At Edcon Steel, we regularly help builders, tradies, and home DIYers across Australia get the most out of their galvanised steel products. Whether you’re building a pergola, fencing a rural property, or finishing off a backyard project, this guide will give you some tips and tricks on how to paint and seal HDG steel the right way.

Please note that all information provided is general in nature, and each reader is responsible for checking with the manufacturer or specifier before relying on any information provided.

“Painting galvanised steel isn’t hard, it’s about doing the prep work right.”

What is HDG steel?

Hot-dip galvanised steel (HDG steel) is steel coated in a layer of molten zinc. This process forms a protective barrier against rust and corrosion, which is why it’s such a popular choice for outdoor use, especially in coastal, industrial, or high-moisture environments.

At Edcon Steel, many of our beams, channels, and structural sections can be hot-dip galvanised after fabrication to provide complete surface protection, including welds and cut areas.

“If you want paint to stick to zinc, there’s no shortcut. You need to clean, etch and prime for good results.”

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Why is preparation so important?

Paint doesn’t naturally stick to zinc coatings, so unless you take the proper steps, it’ll likely peel off. While painting HDG steel takes a bit of prep, you’ll protect your investment and extend the life of the steel, your finish will look clean and professional, and you’ll reduce maintenance time and costs down the track.

Even though HDG steel is highly resistant to corrosion, there are a few good reasons to paint or seal it:

You may want a colour finish to match your build.
Paint adds another layer of defence in harsh environments.
Increased lifespan, particularly in marine or industrial settings.
Branding or safety colours for commercial sites or projects

“At Edcon Steel, we supply HDG steel that’s ready for tough environments and custom finishes.”

Step-by-step: How to paint and seal HDG steel

Supplies checklist

Galvanised steel cleaner or degreaser

Clean water and rags
Sandpaper or a wire brush
Etch primer or galvanised primer
Paint (acrylic, epoxy, or polyurethane
Brushes, rollers or spray equipment
Clear sealer (optional)

Step 1: If possible, let the steel age
If your galvanised steel is fresh from the zinc bath, it’s best to wait a bit before painting. Allowing the steel to weather for a few weeks to a few months helps break down the shiny outer zinc layer.

While this improves paint adhesion, we know that’s not always practical. If you’re working with fresh galvanised steel and can’t wait, no problem. Just follow the rest of the steps closely.

Step 2: Clean the surface thoroughly

Before anything else, the steel surface must be free of grease, dirt, and white rust (zinc oxide). Don’t skip this step! Even fingerprints can prevent paint from bonding properly.

Steps:

Use a degreaser or galvanised steel cleaner to remove contaminants.
Rinse the steel thoroughly with clean water.
Let it dry completely before moving to the next step.

Step 3: Lightly etch the surface

The key to getting paint to stick to your HDG steel is to create a slightly rough, dull surface on which the coating can grip.

There are two main ways you can do this.

1: Mechanical abrasion

Use fine sandpaper, a scouring pad, or even a wire brush to lightly rough the surface. Be gentle, as you don’t want to remove the zinc coating.

2: Chemical etching primer

If you’d rather not sand, use a specialist etch primer designed for galvanised surfaces. These primers contain chemicals that react with the zinc, forming a base layer that paint can adhere to.

Step 4: Apply a suitable primer

Don’t go straight to topcoat! You’ll need to apply a zinc-friendly primer first.

Look for etch primers, galvanised metal primers, or cold galvanising spray primers. These products are designed to bond with the zinc layer and create a stable foundation. Be sure to always follow the manufacturer’s drying times between coats.

Step 5: Choose the right paint

Once primed, you can apply your chosen topcoat. Some good options include acrylic latex paints for light-duty projects, epoxy-based paints for heavy-duty or marine environments, or polyurethane coatings for maximum durability and UV resistance.

Make sure you apply at least two thin coats, allowing enough drying time between each.

Step 6: Seal or clear coat (optional)

If you want an extra level of protection, especially in marine or industrial environments, a clear topcoat or sealer can help extend the life of your paint job.

Always choose paints designed for exterior use and opt for HDG steel and epoxy paint combos for maximum protection. A powder coating may be a better option for visible finishes like pergolas or exposed frames.

“Whether you're building in the bush or by the beach, painting galvanised steel helps protect your structure long-term.”

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At Edcon Steel, we pride ourselves on the expertise of our staff, our level of customer service and the depth of our local market knowledge.

You can visit our stores to browse the range or pick up an online order. Our staff are on hand to answer any questions you have about our full range of products and services, so feel free to contact us for your steel or metal solution today.

5 FAQs About Painting Hot-Dip Galvanised Steel

Can you paint over galvanised steel without priming?

No. Without proper surface prep and priming, paint won’t bond well to zinc. It will likely peel or flake within months.

How do I know if my steel is hot-dip galvanised?

HDG steel usually has a dull, spangled or matte finish. If you’re unsure, ask your supplier. At Edcon Steel, we can tell you exactly what coating your product has.

What’s the best primer for galvanised steel?

Use a zinc-friendly etch primer or galvanised metal primer, as these are specially formulated to bond with zinc coatings.

Can I use regular paint from the hardware store?

You can, but only after priming with the correct product. Without it, even good-quality paints won’t adhere properly to galvanised surfaces.

Do I need to seal painted galvanised steel?

Not always. If the structure is exposed to harsh conditions (like sea spray or industrial fumes), applying a clear sealer or UV-resistant topcoat can help extend the life of your paint job.