How bad is the rust?
Light orange staining or speckles on the surface usually paint well once treated. Rust that bubbles the coating, flakes off in layers or lets pinpricks of daylight into the roof space has gone too deep for paint.
Where it sits matters too. Rust along the laps and around screws is common and treatable, but the screws may need replacing and the laps resealing first. Small scratches are a different matter: BlueScope says scratches under 2 mm wide that you can't see from the ground should be left alone, because the metal coating protects the steel. Our guide to a rusty roof helps you judge yours.
What BlueScope says about painting its steel
It voids the warranty. Overpainting COLORBOND, ZINCALUME or galvanised (zinc-coated) steel voids BlueScope's warranties, and air-dried paint weathers differently from the factory's oven-baked finish.
Water-based acrylic, usually. BlueScope says it's generally the most suitable paint for its coated steel, with a zinc-rich etch primer on rusted areas, and a more corrosion-resistant system, such as a zinc-rich primer, near salty sea air.
Gentle prep. For aged COLORBOND, BlueScope's method is household detergent and water with a mop or soft nylon broom, a fresh-water rinse, then drying time. Steel under about a year old gets a light scuff with kitchen scourer pads, never steel wool. There's no texture match for Matt COLORBOND and no colour match for Metallic.
How a roofer paints a metal roof
Treat the rust
Loose rust is wire-brushed or ground back, and bare steel is primed straight away so it doesn't start rusting again overnight.
Fix before painting
Rusted screws are swapped, laps resealed and any sheet with holes replaced.
Topcoats, gutters and flashings
Usually two topcoats over the primer. Gutters and flashings tend to rust first and are often painted at the same time, or replaced if they're too far gone.
Is it definitely metal?
Painted asbestos cement can pass for metal from the street. ASSEA, the national asbestos agency, says corrugated asbestos cement was made before 1990 and 'Super Six' became a common name for all of it. Hardies kept selling a non-asbestos Super-Six until at least 1992 after dropping asbestos around 1983, so ASSEA says identical sheets not stamped asbestos-free should be treated with caution until tested. Nobody should pressure clean, sand or wire-brush them. See Super Six asbestos roofing.
What's yours to do
You can
- Photograph rust patches from the ground, so you can compare quotes
- With the lights off in the roof space, look for pinpricks of light, which mean rust has gone through
- If the roof feeds a drinking water tank, tell the roofer, because BlueScope says to check the paint suits drinking water
Leave to a roofer
- Wire brushing, grinding and rust treatment
- Every coat of paint, including touch-ups
- Screw, sheet and flashing replacement
- Deciding whether the steel is too far gone to paint
Our honest view
If the rust is surface deep, painting a metal roof is good value, as long as the quote covers rust treatment, screws and a primer that suits your steel. If daylight shows through in several places, we'd price new sheets, or a new roof, before paying for paint. And a Colorbond roof that's just a bit faded can usually wait, especially while it's still under warranty.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.
