Seeing rust on your metal roof doesn't automatically mean a re-roof. Most rust is treatable if caught early, and a lot of what looks like rust isn't rust at all. Here's how we decide treat vs replace.
First: is it actually rust?
A surprising amount of 'rust' on a metal roof is swarf — fine metal filings left from when screws were driven in or sheets were cut. Those filings oxidise onto the coating and look exactly like rust, but they're sitting on the surface. We clean swarf off and treat genuine rust separately. The two need different fixes, and a lot of roofs are needlessly re-roofed because swarf was mistaken for rust.
Surface rust: treat
If the rust is on the surface or at the cut edges and laps, and the sheet is still solid (no pitting, no holes), it's treatable. We remove loose rust, apply a rust converter, prime with a marine-grade primer, and topcoat in a colour-matched finish. Sealing the laps stops moisture re-entering. This costs a few hundred dollars for localised areas.
Cut-edge rust: treat and seal
The exposed cut edge of a Colorbond sheet is where corrosion starts, because the protective coating isn't there. Treating and sealing the edge with a flexible roofing sealant stops it spreading into the sheet. This is the highest-value preventive job on a coastal metal roof.
Rusted-through sheets: replace
If rust has pitted through the sheet metal or you can see pinholes, that sheet is done — no coating will bring it back. We replace the affected sheets, matching the profile and colour, and seal and re-screw the laps with Class 4 fixings. A staged replacement of the worst sheets is far cheaper than a full re-roof.
When a full re-roof is the right call
If rust is widespread across the field of the sheets (not just edges and laps), the roof is 25+ years old, or multiple sheets are rusted through, a full re-roof is better value than treating and replacing piecemeal. We photograph the whole roof and give you an honest cost comparison.
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We're local to Lennox Head and cover the whole Northern Rivers. Every job is photo-documented and warranted.
Coastal Roofing Repairs
Local Northern Rivers roofers · 28 years on the tools · insured
Written by the Coastal Roofing Repairs team, 28 years roofing on the NSW North Coast. We work on coastal metal and tile roofs every day — these guides come straight from what we see on the tools, not a marketing desk.
