Galvanised steel is one of the most durable metals used in construction, gates, railings, cladding, ductwork and agricultural buildings. Its protective zinc coating helps prevent rust, but it also makes painting more challenging than ordinary steel.
If you've ever painted galvanised metal only to see the paint peel away a few months later, poor preparation is usually the reason.
The good news? With the right preparation and primer, you can achieve a durable, long-lasting finish that looks great and protects the surface for years.
Here's how to do it.
Can You Paint Galvanised Metal?
Yes, but you can't simply apply paint directly onto galvanised steel.
Fresh galvanised metal has a smooth, chemically resistant zinc surface that most paints struggle to bond to. Without proper preparation, paint is likely to flake, blister or peel.
The key is to clean the surface thoroughly, chemically etch the zinc coating, apply the correct primer straight away and then finish with a high-quality metal paint.
What You'll Need
Before you begin, gather the following products:
- Coo-Var Universal Degreaser Cleaner
- Teamac Mordant Solution (T-Wash)
- Coo-Var Zinc Phosphate Primer
- A suitable topcoat such as Hammercote Metal Paints
- Clean cloths
- Brushes or rollers
- Clean water for rinsing
Step 1: Clean the Surface Thoroughly
Even new galvanised steel often has oils, grease, dirt or manufacturing residues left behind from production and handling.
If these contaminants aren't removed, they can prevent primers from adhering properly.
Apply Coo-Var Universal Degreaser Cleaner according to the label instructions, working across the entire surface.
Pay particular attention to:
- Grease and oil
- Fingerprints
- Dirt and dust
- Manufacturing residues
Once cleaned, rinse if required and allow the surface to dry completely before moving on.
Top Tip: Even galvanised metal that looks perfectly clean should always be degreased before painting.
Step 2: Etch the Galvanised Surface
This is the step that many DIY painters skip—but it's arguably the most important.
Use Teamac Mordant Solution, sometimes known as T-Wash, to chemically etch the zinc coating.
Rather than simply cleaning the metal, the mordant solution reacts with the galvanised surface to create a key that allows primers and paints to bond properly.
Apply the solution evenly with a brush.
As it reacts, you'll notice the shiny zinc surface gradually changes to a dark grey or black colour.
This colour change shows the treatment has worked.
Once the entire surface has reacted:
- Allow it to dry fully.
- Remove any residue if required by the product instructions.
- Ensure the surface is completely dry before priming.
If any shiny areas remain, reapply the mordant solution until the whole surface has changed colour.
Important: Apply the primer straight after etching with mordant solution to avoid oxidisation.
Step 3: Apply Zinc Phosphate Primer
Now the surface has been properly prepared, it's time to apply a high-performance primer.
Apply one full coat of Coo-Var Zinc Phosphate Primer.
This primer is specifically designed to provide excellent adhesion and corrosion protection on prepared metal surfaces, creating the ideal base for your finishing coats.
Apply an even coat using a brush or roller and allow it to dry in accordance with the product data sheet before overcoating.
Good coverage at this stage will help produce a longer-lasting finish.
Step 4: Apply Two Coats of Metal Paint
Once the primer has fully dried, apply your chosen metal paint.
For long-lasting protection and an attractive finish, Hammercote Metal Paint is an excellent choice.
Apply:
- First coat
- Allow to dry
- Second coat
Two coats provide improved durability, colour retention and weather resistance compared to a single coat.
Hammercote is available in a range of finishes, including:
- Smooth
- Hammered
- Satin
This allows you to choose the appearance that best suits your project while providing excellent long-term protection.
Why Preparation Matters
Galvanised steel is designed to resist corrosion, which is exactly why paint finds it difficult to stick.
Skipping the cleaning or mordant solution stage may save time initially, but often leads to:
- Peeling paint
- Poor adhesion
- Premature coating failure
- Costly repainting
Taking the time to prepare the surface correctly helps ensure your paint system performs as intended.
Frequently Asked Questions
Can I paint new galvanised steel?
Yes, but it should first be thoroughly cleaned and treated with a mordant solution before priming.
What happens if I don't use mordant solution?
Without etching the zinc surface, many paints and primers struggle to adhere properly, increasing the risk of peeling and flaking.
Do I need a primer?
Yes. After the galvanised surface has been etched, applying a quality metal primer such as Zinc Phosphate Primer provides a strong foundation for your topcoat.
How many coats of paint should I apply?
Two finishing coats are recommended for the best appearance, durability and long-term protection.
Can Hammercote be used outside?
Yes. Hammercote is suitable for exterior metal surfaces and provides long-lasting protection when applied over a correctly prepared and primed surface.
The Complete System
For the best long-term results on galvanised metal, follow this complete system:
- Clean using Universal Degreaser Cleaner.
- Etch the surface with Teamac Mordant Solution.
- Prime with Zinc Phosphate Primer.
- Finish with two coats of Hammercote Metal Paint.
By following these four simple steps, you'll create a tough, professional-looking finish that's built to withstand the elements and provide years of protection.
