How to Paint a Colorbond Roof From Wash Down to Top Coat

The painting is the quick part of learning how to paint a Colorbond roof. The result depends on what happens before the first coat goes on, from the inspection to the wash down to the primer choice. Get the prep right and the roof membrane has a clean, sound surface to bond to. Skip it and no amount of top coat will save the job. 

This guide follows the published Dulux Acratex roof membrane system, stage by stage, so you know what to buy and in what order.

The stages at a glance 

1. Inspect the roof and decide if it is a paint job at all 
2. Wash down to remove dirt, chalking and growth 
3. Treat corrosion at screws, laps and cut ends 
4. Prime to suit the condition of the roof 
5. Top coat with a minimum of two coats of roof membrane 
6. Finish details such as edges, pointing and touch-ups 

Stage 1: Inspect first, and know the no-go signs 

Walk the roof (on the fixing lines, where the sheets are supported) before you buy a single tin. You are deciding whether the roof needs paint or needs replacing. 

Signs it is a paint job: 

• The original colour has faded or turned chalky, but the steel is sound 
• Rust is limited to light spots, screw heads or the odd cut edge 
• The sheets are firmly fixed and not leaking 

Signs to stop and rethink: 

• Rust that has eaten through the sheet, or flakes off when you press it 
• Widespread corrosion along laps, gutters or the bottom edges of sheets 
• Sheets that flex, lift or move underfoot 

Paint will not fix holed or structurally tired steel. If that is what you find, a re-roof is the better investment. Browse our Colorbond roofing range and our guide to choosing a Colorbond roof colour that flatters your home. 

Stage 2: Wash down and de-chalk properly 

Aged Colorbond often develops a fine powdery layer called chalking. The Dulux data sheets are clear that the surface must be clean, dry and free of dust, dirt, grease and other contaminants before coating, so the chalk has to go. 

• Kill growth first. Where moss, lichen or algae are present, the Dulux system uses Acratex PrepTreat and allows it at least two hours to dry before the next step. 
• Wash with the laps, not against them. Work the spray down the slope, in the same direction water runs off the roof. Driving a high-pressure jet up the slope or into side laps can force water underneath the sheets. 
• Rinse gutters as you go, so sludge does not dry back onto clean steel. 
• Let it dry completely. Coating over a damp roof is one of the easiest ways to compromise adhesion. 

If you collect rainwater, disconnect the tank downpipes before washing and keep them off for the whole job. Check each product’s data sheet for when it is safe to reconnect. 

Stage 3: Treat corrosion at screws, laps and cut ends 

Rust tends to start in the same places: around screw heads, along laps where water lingers, and at cut ends of sheets. 

• Clean rusted areas back to bright metal with a wire brush or power tool, as the Dulux data sheets describe 
• Apply the rust treatment and spot priming that the Dulux metal roof guide specifies for your roof’s condition before the full primer coat 
• Replace screws that are past saving. If a screw head is rusted through or the washer has perished, swap it out now so the new fixing is primed and coated with the rest of the roof. You will find replacements in our screws range. 

Stage 4: Prime to suit the roof’s condition 

Primer choice depends on what the roof is made of and what state it is in. Dulux sets this out in its metal roof application guide, which matches each roof condition to a primer. 

• Dulux Acratex Roof Primer MX Plus (15 L) is the Dulux metal primer for aged Colorbond, Zincalume, galvanised steel and aluminium. Dulux also notes it suits colder weather in southern states, which makes it a practical pick for Victorian roofs. 
• Aged, chalked Colorbond in good condition is one case where the Dulux guide lists no primer under certain membrane finishes, so check the guide against your roof before you buy. 
• New or near-new Colorbond uses a different primer in the Dulux system, so this one also needs checking first. 

Have a tiled section too? Some homes have a metal extension next to a concrete tile roof. For the tiles, the Dulux system uses Dulux Acratex Roof Sealer WB (15 L), a water-based sealer for correctly prepared concrete roof tiles. It is not a metal primer, so keep the two separate. 

You can browse the full range in our Dulux category and the wider paint range. 

Stage 5: Top coat with roof membrane 

This is where the colour goes on. Dulux Acratex Roof Membrane is a high-build, water-based 100% acrylic coating for metal and concrete roofs, available in satin or gloss. 

What the Dulux system asks for: 

• A minimum of two coats of roof membrane over the correctly prepared and primed roof 
• Recoat times as stated on the data sheet, which are measured at set temperature and humidity conditions and run longer in cool, damp or still weather 
• Extra material for profiled sheets. Dulux notes a profiled roof has more surface area than a flat one of the same footprint, so allow for that when you order 
• Enough tinted stock to finish in one go, so the colour stays consistent across the roof 

Weather matters just as much. The Dulux data sheets advise against applying in hot, windy conditions or onto hot surfaces, and the coating must be protected from rain and dust during application. On a Melbourne summer day, a dark metal roof gets very hot by mid-morning, so plan your coats around cooler parts of the day and a clear forecast. 

For more on why the membrane approach suits Australian conditions, read why choose Dulux roof membrane for your roof restoration and Dulux Acratex roof membrane vs the Aussie sun. 

Stage 6: The details that decide the look 

A roof restoration lives or dies on its edges. 

• Gutters and fascias: cut in neatly where the roof meets the gutter, and decide early whether gutters and fascias are being repainted too, so the colours match 
• Tiled ridges: where a tiled section has loose or cracked ridge pointing, repoint it with Dulux Acratex Roof Pointing, a water-based acrylic pointing mortar for concrete ridge tiles, before sealing and coating 
• Touch-ups: keep a little of the same batch aside for scratches from foot traffic or later trades 

Curious how the membrane handles small surface cracks? See how Acratex roof membrane prevents roof cracks, and for a wider comparison, the advantages of Dulux roof painting over ordinary roof paint. 

Can you paint a metal roof yourself? 

Many homeowners do, but be realistic about working at height: 

• Only work on a dry roof in calm weather, as wet paint and dew make metal slippery 
• Secure your ladder, use edge protection or a harness where the height and pitch call for it, and never work alone 
• Keep spray equipment, hoses and tins tied off or in a tray, not loose on the slope 

Dulux also runs an applicator scheme for professional roofers. On a steep, high or complex roof, buying the materials and engaging an experienced applicator is often the safer path. 

Frequently asked questions 

What is the best month to paint a roof in Victoria? 

There is no single best month. What matters is meeting the Dulux application conditions: a dry roof, no rain expected, and no hot, windy weather or hot surfaces. Mild, settled spells make those easier to meet, so pick your days by the forecast rather than the calendar. 

How many coats does a Colorbond roof need? 

The Dulux Acratex system calls for a minimum of two coats of roof membrane over a correctly prepared and primed roof. Check the data sheet for your chosen finish. 

Can I spray or should I roll Colorbond roof paint? 

The roof membrane can be applied by brush, roller or spray. The Dulux system documents describe airless spray for full roof coats, while a brush or roller is handy for edges and touch-ups. 

What happens if I paint over chalking without cleaning it? 

The coating bonds to the loose chalk instead of the sound surface underneath. That is why the Dulux data sheets require a clean, dry, contaminant-free surface before any coat goes on. 

Do I replace the screws before or after painting? 

Before. Replacing rusted or failed screws first means the new fixings are primed and coated along with the rest of the roof, so everything matches and is protected. 

Planning a Colorbond roof repaint? Browse the Dulux range or call the Truganina team on (03) 9394 1400 and we will help you put together the right system for your roof. We deliver Australia-wide.