Over time the surface of galvanised metal deteriorates as the electrochemical process of corrosion breaks down the metal's zinc layer. Protecting old galvanised metal by painting its surface, however, maintains the structural integrity of the metal and extends the product's lifespan. According to the American Galvanizers Association, a galvanised coating exposed to the outside elements for at least a year tends to experience paint adhesion difficulty that is primarily due to the lack of appropriate surface preparation. It is critical, therefore, to utilise the right procedures and primer system in order to effectively prepare the galvanised metal for successful paint adhesion.
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Things you need
- Wire wool
- Hand brush
- Water-based degreaser
- Zinc phosphate primer
- Anti-corrosive epoxy primer
- Acrylic polyurethane paint
- White spirit
- Alkaline-based degreaser
- Rubber gloves
- Safety glasses
Remove all surface rust and brittle galvanised scales using wire wool. Sweep the debris from the old galvanised metal surface using a hand brush. Use a new piece of wire wool and lightly abrade the whole surface.
Scrub the galvanised metal with a water-based degreaser and a cloth to remove dirt and oil deposits. Rinse the surface with hot water to remove the degreaser chemicals. Dry the old metal with a cloth in order to quickly remove excess water and allow the metal surface to completely dry.
Amalgamate the zinc phosphate primer to an even consistency using a stir-stick. Apply the primer with a paintbrush over the entire surface to create a cold galvanising layer that repairs the deteriorated galvanised coating. Allow the zinc phosphate primer to dry according to the manufacturer's instructions.
Mix the anticorrosive epoxy primer with a stir-stick to amalgamate the solution. Apply the epoxy primer over the zinc phosphate coating with a paintbrush to provide an additional anti-corrosion layer and help with effective paint adhesion. Allow the coating to dry.
Mix the acrylic polyurethane paint with a stir-stick until the colour is uniform. Using a paintbrush, apply the paint over the anticorrosive epoxy primer and allow the surface to dry.
Apply a second coat of acrylic polyurethane paint to the surface to complete the painting procedure for old galvanised metal. Allow the coating to fully cure according to the manufacturer's instructions before using the metal product.
Tips and warnings
- If the water-based degreaser is not strong enough, remove thick oil deposits with white spirit or an alkaline-based degreaser; wash off the chemicals from the metal with hot water.
- Use an alkaline-based degreaser with a pH between 11 and 12 to avoid damaging the zinc.
- Wear rubber gloves and apron, safety glasses and a respirator to avoid dust and chemical ingestion.
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