How do you repaint rusted metal so the rust stays away?

Can you paint over rust? Yes, once the loose, flaky rust is off

You can paint over small bits of rust, but the loose, flaky rust has to come off first. Dulux's instructions for its Metalshield Rust Primer say to remove any loose, flaky rust by scraping, sanding with P320 sandpaper or wire brushing.

You don't have to get the metal back to shiny, though. Asked whether rust needs to come off totally, Dulux says no. Small bits of rust left on the metal get converted to an inert form by the primer, which stops more rust forming.

That's why the primer matters so much. Dulux says its rust primer is designed to neutralise rust and stick to rusted surfaces, so the topcoat lasts longer. A plain topcoat rolled straight over a rusty gutter skips the step that deals with the rust.

The Queensland Government says homes built before 1970 have probably had lead-based paint used, so have old paint on an older house tested before you sand or scrape it.

How to repaint rusted metal, step by step

Here's the method in six steps, built from the instructions on Dulux's Metalshield Rust Primer page. They suit a letterbox, a gate or a rusty patch on a low fascia you can reach from the ground.

1. Pick your day. Dulux says it must stay above 10°C while the primer goes on and dries.
2. Get the loose rust off. Scrape, sand with P320 paper or use a wire brush. Small bits of rust can stay.
3. Clean it. Dulux says to wipe off all grease, oil and rust residue with mineral turps, then let it dry completely.
4. Prime straight away. Dulux says to prime right after prep for the top result. Put on one or more coats by brush, roller or spray.
5. Don't panic at the colour. Dulux says the primer darkens wherever it goes over rust.
6. Topcoat inside a week. The primer is touch dry in 30 minutes and ready to recoat in an hour, and Dulux says it must be overcoated within 7 days.

For the topcoat, Dulux pairs the primer with Metalshield Rust Defence, a fast dry modified acrylic topcoat that comes in gloss or satin. Whatever you pick, keep the primer and topcoat from one maker. BlueScope recommends not mixing paints from different suppliers.

What deals with rust before painting: a rust converter or a rust primer

A rust converter or a rust-converting primer is what deals with the rust left after prep. In the four-step method Dulux says most metal products use, a rust converter goes on before the primer. Its 2-in-1 rust primer does both jobs in one product.

Damaged galvanised steel is a different case. Dulux makes Metalshield Cold Galv Primer for repairing it. Dulux says its zinc-rich formula forms a sacrificial barrier against corrosion. There's a catch, though. It can't go on top of existing paint. Dulux gives prep steps for aged or lightly rusted metal and for bare galvanised iron and Zincalume.

Which one suits your metal depends on what it is and how bad the rust is.

Colorbond and Zincalume gutters: you can paint them, but the warranty goes

Yes, you can paint Colorbond and Zincalume gutters and fascias. BlueScope's overpainting bulletin says its coated steel can be successfully overpainted. The same bulletin says overpainting Colorbond, Zincalume or zinc-coated steel voids any warranty BlueScope issued. So check your warranty before you start.

BlueScope says water-based acrylic is generally the most suitable paint type for its steel. For Colorbond that's had more than a year of weather, its prep goes like this.

1. Wash with household detergent and water, using a mop or a soft nylon broom. Rinse and let it dry.
2. Lightly roughen the surface with kitchen scourer pads so the paint can grip. Not steel wool. BlueScope says steel wool leaves tiny metal bits that can damage and stain the steel.
3. Wash and rinse again, then let it dry.

Rust spots on Zincalume or zinc-coated gutters get a different fix. BlueScope says to brush all the rust off with a stiff nylon bristle brush, taking only the rust and not the metal coating. Then thinly apply a zinc rich etch primer before the topcoat.

Small scratches should be left alone. BlueScope doesn't recommend touch-up paint on Colorbond, and says scratches under 2mm wide that you can't see from the ground should be left. BlueScope says painted areas may weather at a different rate to the factory finish and look different over time.

Salt air on the Sunshine Coast: beachside metal may need a tougher paint system

BlueScope lists Sunshine Coast beaches as an example of its surf class, one of its three salt marine classes (surf, exposed and calm). Surf means areas exposed to breaking surf and ocean spray. BlueScope says its classes are based on the Australian Standard AS 4312:2019 for corrosion zones.

BlueScope calls it a guide only. It says prevailing winds, shelter, height above the water and unwashed areas can all affect how much the salt bites. And for more corrosive salt marine sites, its overpainting bulletin says you may need a paint system with better corrosion resistance, like one with a zinc-rich primer.

Distance from the water matters when gutters get replaced, too. BlueScope's gutter guide recommends standard Colorbond and Zincalume more than 200m from the high water mark, and Colorbond Ultra steel more than 100m from it.

A bit of care keeps rust from starting again:

• Hose the hidden bits. Colorbond says spots rain doesn't wash, like the underside of eave gutters, need hosing at least every six months, and more often near the coast.
• Keep water moving. BlueScope says water pooling in a gutter can speed up corrosion.
• Check the air con pipe. BlueScope says condensate piped into gutters can cause early corrosion. It should run to the ground.

For the walls around those gutters, see the best exterior paint for coastal homes and how long exterior paint lasts.

Second-storey gutters and roof-edge work are a job for a painter

Gutters and fascias up on a second storey, or anything you'd reach from the roof, are a job for a professional. Queensland's Office of Fair Trading says ladders cause more DIY-related deaths and hospital stays than any other consumer product.

If you're on a ladder at all, the Office of Fair Trading says keep three points of contact and don't use it in high winds, rain or storms. BlueScope's bulletin tells painters to follow local working at heights laws. In Queensland, a code of practice covers managing the risk of falls at workplaces.

Stop the DIY at ground level. If the rusty gutter is above a single-storey fascia line, or you'd need to stand on the roof, get a painter in.

What repainting eaves, fascias and gutters costs on the Sunshine Coast

Eaves, fascias and gutters on a single-storey home in good condition come in at $1,500 to $4,500 in our instant estimate. That's a standard repaint, a guide range including GST and rounded to $100. It's not a quote. The firm price comes after a free site visit.

For how that stacks up against a full exterior, see exterior house painting cost, or read the full guide to painting a house exterior. We've painted Sunshine Coast homes since 1985 and hold QBCC licence 1281728. Our exterior house painters work from Caloundra to Noosa, including house painters in Pelican Waters and Caloundra. See every suburb we cover.