Rust spots on a corrugated iron roof are a common headache for NZ homeowners, especially in coastal or high-rainfall areas. The good news is that small, isolated rust patches can often be treated as a DIY job — as long as you catch them early, use the right products, and work safely at height. Left untreated, rust will spread and eventually cause leaks, so it pays to act promptly.
Safety First — Working at Height
Before you climb onto your roof, take a moment to plan your safety. Falls from roofs are one of the leading causes of serious injury in New Zealand. WorkSafe NZ recommends using a properly secured ladder, wearing non-slip footwear, and never working alone. Walk only on the ridges (high points) of corrugated iron to avoid denting or cracking the sheets, and avoid working in wet or windy conditions. If your roof pitch is steep (generally over 25°), or you're not confident working at height, it's best to call a professional roof painter.
Assess the Damage First
Not all rust is the same. Before you start, check whether you're dealing with:
- Surface rust — orange staining with no pitting; easiest to treat
- Pitted rust — the metal has started to corrode through; needs more work
- Rust-through holes — the iron has corroded completely; may need sheet replacement
If you find holes or widespread corrosion across large areas of the roof, this goes beyond a DIY touch-up. A licensed roof painter or roofing contractor will give you an honest assessment.
What You'll Need
| Item | Purpose |
|---|---|
| Wire brush or angle grinder with wire wheel | Remove loose rust and scale |
| Coarse sandpaper (80–120 grit) | Feather edges and key the surface |
| Clean rags and solvent (e.g. methylated spirits) | Degrease before painting |
| Rust converter | Chemically neutralises remaining rust |
| Zinc-based primer or rust-inhibiting primer | Seals and protects bare metal |
| Quality roof paint (acrylic or oil-based) | Topcoat matched to existing roof |
| Paintbrush and/or small roller | Application |
| Safety gear: gloves, safety glasses, non-slip boots | Personal protection |
Step-by-Step: Treating Rust Spots
1. Remove Loose Rust
Using a wire brush or angle grinder with a wire wheel attachment, scrub away all loose rust, flaking paint, and scale. Work back to a firm edge. If you're using a power tool, wear safety glasses and a dust mask — rust particles are harmful to breathe in.
2. Sand and Feather the Edges
Sand the area with 80–120 grit sandpaper to smooth the transition between bare metal and the surrounding painted surface. This helps the new paint bond properly and prevents early peeling.
3. Clean and Degrease
Wipe the area down thoroughly with a clean rag dampened with methylated spirits or a suitable solvent. Remove all dust, grease, and grime. Allow to dry completely before applying any product.
4. Apply Rust Converter
Rust converter is a chemical treatment that reacts with iron oxide (rust) and converts it into a more stable compound, stopping further corrosion. Apply it to any remaining rust staining with a brush, following the manufacturer's instructions. Most products require 15–30 minutes to react and will turn the rust black or dark grey. Allow to cure fully before moving on.
5. Prime the Bare Metal
Apply a zinc-based or rust-inhibiting primer to the treated area. This is a critical step — skipping primer is one of the most common reasons DIY rust repairs fail early. Resene and Dulux both offer suitable metal primers; check the product data sheet to confirm compatibility with your topcoat. Allow the primer to dry fully as per the label.
6. Apply the Topcoat
Finish with a quality roof paint that matches your existing colour as closely as possible. Wattyl and Resene both stock roof paints formulated for corrugated iron in NZ conditions. Apply one or two coats, allowing full drying time between coats. A small brush is useful for working into the corrugations.
7. Inspect Your Work
Once dry, check for any missed spots, thin coverage, or areas where the paint hasn't bonded well. Touch up as needed.
Choosing the Right Paint for NZ Conditions
NZ's UV levels are among the highest in the world, and coastal areas bring salt-laden air that accelerates corrosion. Choose a paint specifically rated for metal roofing with good UV resistance. If your roof is near the coast, look for products with enhanced corrosion resistance. Always check the product's technical data sheet — reputable brands like Resene and Dulux publish these online and their in-store staff can advise on the best system for your situation.
Do You Need a Building Consent?
For like-for-like maintenance painting and minor rust repairs, a building consent is generally not required. However, if you're replacing roof sheets or making structural changes, check with your local council — some work may require consent. MBIE Building Performance has guidance on Schedule 1 exemptions, but your council has the final say.
When to Call a Professional
Call a qualified roof painter or roofing contractor if:
- Rust covers a large area or multiple sheets
- You find holes or significant pitting through the iron
- The roof pitch is steep or access is difficult
- You're not confident working safely at height
- The roof is old and may need full replacement rather than patching
A professional will have the right equipment, commercial-grade products, and experience to get a lasting result. You can find qualified local roof painters on tradedirectory.co.nz.
Master Painters NZ member
Licensed Building Practitioner (LBP)
Roofing Association of NZ (RANZ)
