How to Paint Galvanised Steel, Aluminium and Other Bare Metals

Choosing the wrong undercoat is the most common reason metal paint projects fail. Unlike timber or plasterboard, metal surfaces are completely non-porous and chemically reactive. Applying ordinary paint directly to steel, aluminium, or galvanised iron leads to rapid peeling and rust. Metals lack the natural profile required for ordinary paints to grip, meaning a specialised primer acts as a critical link. It chemically or mechanically bonds to the bare metal while providing a textured surface for the topcoat to adhere to.

Positioned at the forefront of Australian manufacturing since 1935, Haymes Paint is a family-run business born in Ballarat, now in the hands of the fourth generation. This long history of local manufacturing highlights our expertise in crafting products specifically calibrated for the unique quality of Australian light and environmental conditions. Learn how to identify your metal surface, select the correct primer, and apply a professional system that shields your metal for years.

Why metal surfaces demand a dedicated paint primer

Priming is non-negotiable for metal surfaces due to their physical and chemical properties. Ferrous metals, which contain iron, oxidise rapidly when exposed to moisture and oxygen, forming destructive rust. Non-ferrous metals, like aluminium, brass, or copper, do not rust in the traditional sense, but they form a naturally smooth, non-porous oxide film that resists standard paint adhesion, causing ordinary paints to peel off in sheets.

Applying a dedicated primer solves both of these issues:

• Adhesion: Specialised primers are formulated with active resins that bite into smooth metal surfaces, establishing a secure physical and chemical bond.
• Corrosion Protection: Primers designed for ferrous metals contain anti-corrosive pigments that chemically inhibit rust development.
• System Integrity: The primer acts as a stable foundation, ensuring the final topcoat applies evenly and achieves its maximum performance life.

Start by identifying your metal substrate

Before purchasing any products, you must identify the exact type of metal you are working with, as primers are not interchangeable.

1. Ferrous Metals: Steel, wrought iron, and cast iron are highly magnetic and prone to rust. If a magnet sticks firmly to the bare surface, it is a ferrous metal.
2. Non-Ferrous Metals: Aluminium, copper, and brass are non-magnetic and do not rust, though they can oxidise.
3. Zinc-Treated Metals: Galvanised steel, Zincalume®, and Zincanneal® are steel surfaces coated in zinc to prevent corrosion. They are magnetic but require specialised non-ferrous preparation due to their zinc skins.

If you are working over a previously painted surface, you must diagnose its structural integrity. Do not guess whether the existing paint is sound, use these two simple tests:

• The Adhesion Test: Lightly cut an 'X' shape through the existing paint layers down to the substrate using a sharp utility knife. Press a piece of high-tack adhesive tape firmly across the centre of the 'X' cut. Grip the end of the tape and pull it off sharply in a single, fast motion. If any of the old paint pulls away with the tape, or if the paint easily lifts off the substrate around the cut, the existing paint system lacks structural integrity and must be fully removed before repainting.
• The Compatibility Test: Test for compatibility with a previous paint by sanding and cleaning a small, inconspicuous area. Apply one coat of the desired topcoat and allow it to dry. After 24 hours of drying time, conduct a standard adhesion test directly over the newly painted spot. If the tape removes the new paint, the old and new paints are incompatible, requiring a full strip back to bare metal.

Choosing a primer for mild steel and wrought iron

Mild steel and wrought iron are highly vulnerable to corrosion. Once cleaned of all dust, grease, and dirt, bare steel must be primed immediately to prevent rusting.

For bare, unpainted mild steel and wrought iron, the standard professional pathway is MetalPlus Etch Primer. Formulated as a chromate-free undercoat, it chemically bites into bare steel surfaces to deliver exceptional adhesion and robust anti-corrosion protection.

• Application: Apply one to two coats of Etch Primer using a high-quality synthetic brush, roller, or spray.
• Drying Time: It is touch dry in just 40 to 60 minutes under standard conditions, allowing for efficient project progress.
• Clean-up: Clean all equipment with MetalPlus Brushable Enamel Thinner.

Priming aluminium to prevent paint peeling

Aluminium is lightweight and naturally corrosion-resistant, but its smooth oxide layer is notoriously difficult for standard paints to grip.

To prepare and paint aluminium successfully:

1. Clean: Wash the surface thoroughly with sugar soap and rinse with clean water to remove all dirt and grease.
2. Abrade: Rub the surface thoroughly using a non-metallic scourer. This scuffs the smooth oxide film without embedding iron particles, which would cause galvanic corrosion.
3. Prime: Apply one coat of MetalPlus Etch Primer. The chromate-free formula provides a robust physical grip over aluminium, ensuring your topcoat will not peel.

Priming galvanised steel and zinc treated surfaces

Zinc-treated metals, including galvanised steel, Zincalume®, and Zincanneal®, have oily manufacturing residues or chemical passivation treatments on their surfaces that must be completely neutralised.

To prepare and prime these surfaces:

1. Degrease: Apply a solvent degreaser to dissolve manufacturing oils.
2. Wash: Scrub the surface thoroughly with a non-metallic scourer and sugar soap, then rinse completely with clean water.
3. Sand: Once dry, sand the surface lightly to promote mechanical adhesion, and clean down once more.
4. Prime: For bare Galvanised Steel, apply one coat of MetalPlus Etch Primer. For Zincalume® and Zincanneal®, apply MetalPlus Universal Primer or Etch Primer. MetalPlus Universal Primer is a versatile, high-build solvent-based primer that delivers an exceptionally smooth, heavy foundation.

Repairing damaged galvanised steel with a zinc rich primer

When galvanised steel is cut, welded, drilled, or deeply scratched, its protective zinc layer is broken, leaving the underlying steel exposed to rapid rusting. In these situations, standard etch primers are insufficient.

You must apply MetalPlus Cold Gal to the damaged areas. This is a specialised, zinc-rich primer containing high-build zinc pigments designed to provide sacrificial galvanic protection. It essentially replates the exposed steel, preventing rust from forming or creeping beneath the adjacent sound galvanised skin.

• Application: Apply one to two coats by brush to achieve a high-build barrier, or use the convenient aerosol format for hard-to-reach welds.
• Drying Time: Liquid Cold Gal is touch dry in 30 to 40 minutes, while the aerosol format dries in 20 minutes. Allow 16 hours before recoating or applying your topcoat.
• Clean-up: Clean equipment with MetalPlus Brushable Enamel Thinner.

Treating rusted steel and wrought iron before priming

While we focus on bare metals, you will often encounter minor rust on older steel structures. For the longest-lasting paint finish, you should always scrape and sand back to bare steel. However, if minor, tight surface rust remains after thorough sanding, you can isolate it chemically.

Apply MetalPlus Rust Converter Primer Sealer directly to the tightly bound rust. This product chemically converts iron oxide into a stable, paintable organic barrier in one easy step.

• Drying and System Build: The converter dries in two to three hours and washes up easily with water. For robust protection in exterior or highly exposed environments, apply one coat of MetalPlus Universal Primer directly over the converted rust before applying your topcoat.

Priming previously painted metal surfaces

If you are working over existing paint, your preparation pathway depends entirely on the results of your tape adhesion test:

• Existing Paint in Good Condition: If the old paint is sound and tightly bound, sand any minor rust spots back to bare metal. Wash the entire surface clean using MetalPlus Brushable Enamel Thinner. Once clean and dry, you can apply your topcoat directly to the prepared surface without an additional undercoat.
• Existing Paint in Poor Condition: If the old paint is peeling, flaking, or cracking, scrape away all loose material. Sand the remaining paint edges to a smooth, feathered, dull finish. Clean the surface, then apply one full foundation coat of MetalPlus Universal Primer over the entire area to seal the surface and provide a uniform grip.

Metal primer selection guide

To simplify your product selection, use this table to match your metal substrate and surface condition to the correct MetalPlus preparation system:

Completing your project with premium metal paint

Priming is only half of the protective system. To shield your metal from Australia's intense UV radiation and harsh weather, you must apply a high-performance topcoat.

MetalPlus UV Superior Enamel is formulated with advanced silicon alkyd technology, delivering exceptional colour and gloss retention even under direct sunlight. It acts as Step 3 of the system, sealing the primed surface and providing a durable, weather-resistant barrier.

• Aesthetic Options: The product is available in pre-tinted, popular Colorbond colours and is tintable to over 15,000 custom shades at selected stores, making it easy to coordinate with your home's trim, gutters, or roofing.
• Finish Levels: Choose from Gloss, Satin, or Matt finishes to suit your style.
• Application Standards: Stir thoroughly with a broad flat stirrer. Apply two coats by brush, roller, or spray. Under standard conditions, it is touch dry in 4 hours and ready for a second coat after 16 hours. Thinning is not recommended unless spraying, in which case you can add up to 100mL of MetalPlus Brushable Enamel Thinner per litre.
• Clean-up: Clean brushes and rollers immediately with MetalPlus Brushable Enamel Thinner.

Summary and next steps

Using a substrate-specific primer is the single most important factor in preventing peeling and rust on bare metal. By matching your steel, aluminium, or galvanised surfaces to the correct MetalPlus range, you ensure a professional-grade finish that protects your valuable assets.

Ready to select your colours and purchase your metal paint system? Find a store near you page to locate your nearest independent stockist among over 350 locations across Australia, or browse the complete range online to download detailed Product Data Sheets.