Sealing exposed nail heads on a corrugated iron roof is one of the most important preparation steps before painting. Skip it, and you risk rust streaks, leaks, and paint failure within a season or two. Done properly, it takes only a few hours and can add years to your roof's life.
Why Exposed Nail Heads Are a Problem
On older New Zealand iron roofs — particularly those fixed with clout nails rather than modern screws — the nail heads sit proud of the surface and are constantly exposed to rain, UV, and temperature swings. Over time, the original sealant or paint around each nail breaks down, allowing:
- Rust to form around and under the nail head
- Water ingress through the nail hole into the roof cavity
- Paint to lift and peel around each fixing point
Addressing these before painting is standard trade practice and is strongly recommended by coating manufacturers.
Safety First
Working on a roof carries serious fall risk. Before you climb up:
- Use a roof ladder (one that hooks over the ridge) and set up edge protection or scaffolding where required.
- Never work on a wet or dewy roof — iron becomes extremely slippery.
- Check WorkSafe NZ guidelines on working at height before starting.
- If the roof pitch is steep or you're not confident, engage a qualified roof painter — you can find local professionals on tradedirectory.co.nz.
What You'll Need
| Item | Purpose |
|---|---|
| Wire brush or angle grinder with wire wheel | Remove loose rust and old sealant |
| Rust converter (e.g. Dulux or Wattyl brand) | Neutralise active rust before sealing |
| Roof and gutter silicone or butyl-based sealant | Seal around each nail head |
| Roofing primer (oil-based or rust-inhibiting) | Prime bare metal and nail heads |
| Putty knife or caulking gun | Apply sealant neatly |
| Safety glasses, gloves, non-slip footwear | Personal protection |
Step-by-Step: Sealing Exposed Nail Heads
1. Inspect and Identify All Nail Heads
Walk the roof carefully (stepping on the ribs, not the pans, to avoid denting) and mark any nail heads that are lifting, rusted, or missing their original sealant cap. On older roofs, this can be nearly every nail.
2. Remove Loose Rust and Old Sealant
Use a wire brush or angle grinder with a wire wheel attachment to clean back each nail head to bare, sound metal. Remove any flaking paint or crumbling old putty. Vacuum or brush away all debris.
3. Apply Rust Converter (If Active Rust Is Present)
If the nail heads or surrounding iron show orange or red rust, apply a rust converter product according to the manufacturer's directions. This chemically neutralises rust and provides a stable base for your sealant and primer. Allow full cure time — typically a few hours, but check the product label.
4. Seal Each Nail Head
This is the key step. Apply a roofing-grade sealant — a butyl rubber or polyurethane-based product designed for metal roofing — around and over each nail head using a caulking gun. Work the sealant into the gap between the nail head and the iron sheet, then feather the edges outward so water cannot pool against the seal. Avoid standard bathroom silicone, as it doesn't bond reliably to metal and won't accept paint.
Some tradespeople use a reinforced roofing membrane tape (a self-adhesive bitumen or butyl tape) over nail heads for extra security, particularly on older roofs with larger gaps. This is a sound approach on roofs with significant movement or corrosion.
5. Prime the Sealed Nail Heads
Once the sealant has cured (check the product's recoat time), apply a rust-inhibiting roofing primer over each nail head and the surrounding area. Products from Dulux, Wattyl, or Resene all offer suitable roofing primers — check each brand's roofing system guide to ensure compatibility with your topcoat.
6. Full Roof Prime and Paint
With all nail heads sealed and primed, you can proceed with priming the full roof surface and applying your chosen roofing topcoat. Always follow the coating manufacturer's full system — using a primer and topcoat from the same brand is the safest way to ensure adhesion and warranty coverage.
Choosing the Right Sealant
Not all sealants are equal for this job. Look for products specifically labelled for metal roofing or roof and gutter use. Key properties to look for:
- Paintable — many silicones are not paintable; check the label
- UV stable — important in the NZ climate
- Flexible — iron roofs expand and contract significantly with temperature changes
- Waterproof — obviously essential
You'll find suitable products at Bunnings, Mitre 10, or PlaceMakers. Ask staff to confirm the product is paintable before you buy.
Does This Require a Building Consent?
Repainting and sealing an existing roof is generally maintenance work and does not require a building consent under Schedule 1 of the Building Act. However, if you are replacing roof cladding or making structural changes, consent may be required. Always confirm with your local council if you're unsure. See MBIE Building Performance for general guidance.
When to Call a Professional
Consider hiring a qualified roof painter if:
- The roof pitch is steep or access is difficult
- There is widespread rust, significant corrosion, or multiple leaking nail holes
- You're unsure which products are compatible with your existing coating
- You want the work to be covered by a professional warranty
A professional roof painter will have the right equipment, know the best products for your specific roof type, and can spot other issues (like failing laps or ridge cap problems) while they're up there. Find qualified local roof painters on tradedirectory.co.nz.
Master Painters NZ member
Licensed Building Practitioner (LBP)
Roofing Association of NZ (RANZ)
