Rust stains bleeding through paint at every nail head

Rust stains at every nail head mean the nails are corroding underneath the paint and the rust is bleeding out through the film. Painting straight over them hides the marks for a few months at most, and they return in exactly the same places, usually darker than before.

This is one of the most common findings on Wellington weatherboard houses, and it is almost always a fixings problem rather than a paint problem.

Why are the nails rusting?

Most 1900s to 1930s weatherboard homes here were fixed with plain or galvanised steel nails. Galvanising is a sacrificial zinc coating and it does not last forever. It wears through when boards are sanded, it is cut through when a nail is punched below the surface, and it is consumed steadily by salt in the air. Once the zinc is gone the steel rusts, and rust expands. That expansion cracks the paint directly over the head, water gets in, and the whole thing accelerates.

Salt makes it dramatically worse. How much sea spray a site takes is the thing that decides how long a fixing lasts, and plenty of Wellington sits at the harsher end of that: the south coast, the harbour edge, and exposed ridges that take the full southerly. Close to the sea, fixings need to be stainless steel, and the more spray a site gets the more that matters. A hundred-year-old villa was not built with any of it. If you are re-fixing boards on an exposed site, ask your building merchant which stainless grade suits your exposure rather than taking whatever is on the shelf, because the grades are not interchangeable near the coast.

Newer work is not automatically safe either. Electro-galvanised gun nails in a coastal location will rust out well inside the life of a paint system, and plain bright steel nails used by mistake will show within a year.

Is it definitely rust?

Three different problems produce brown marks on a painted wall, and they need three different products. Work out which one you have before buying anything.

Clue	Rust from a fixing	Tannin bleed from the timber	Mould
Pattern	a dot at the centre of each mark, evenly spaced in rows	streaks running down from joints, knots and end grain	patchy, worst on shaded damp elevations
Colour	orange to red-brown, darkest at the centre	tea brown with soft edges	black, grey or green specks
Feel	often a hairline crack or a raised bump you can catch a fingernail on	flat, sitting in the film	flat, partly wipes away
Movement	fixed positions, never spreads sideways	runs downhill with rainwater	spreads outward over months
Response to washing	no change	little change	visibly reduces

Does it mean the weatherboards need replacing?

Usually not. Rust staining on its own is a surface problem. Push a screwdriver into the timber immediately around a stained nail. If it is firm, the board is fine and the fixing is the only issue.

What does justify replacement is a nail head that has rusted away to nothing, leaving the board loose at that point, or soft punky timber around the hole where water has been sitting for years. A board that moves when you press it, or has sprung away from the framing at one end, means fixings have failed structurally and a builder should look before a painter does.

How do you stop it properly?

1. Scrape and sand the cracked paint back around each stained nail, far enough to expose the head and a small ring of sound timber.
2. Punch the head a couple of millimetres below the surface. That takes the corroded metal out of the paint plane and gives you a recess to fill.
3. Wire brush or abrade the head until you are onto clean metal. Rust left in place carries on working under whatever goes over it.
4. Spot-prime the head with a rust-inhibitive metal primer. This is the step that gets skipped, and skipping it is why the stain comes back.
5. Fill the recess with an exterior grade flexible filler, let it cure properly, sand flush.
6. Seal the filled spot and any residual staining with a pigmented stain-blocking primer. Waterborne topcoats on their own will not hold rust back.
7. Two full topcoats across the whole elevation, not just the patches, or every repair will show in raking light.

Where the fixings have really gone, the better long-term answer is to re-fix the affected boards with stainless nails and treat the old heads as above. It costs more on the day and it is the last time you deal with it.

What does each approach actually get you?

Approach	What it involves	Realistic result
Paint straight over	wash and two coats, no fixing work	stains reappear within a season, darker than before
Spot-treat the worst	punch, prime and fill the obvious offenders only	a few years before the untreated nails come through
Treat every fixing on the elevation	systematic punch, clean, prime, fill and seal	matches the life of the paint system
Re-fix with stainless	supplement or replace corroded nails with stainless fixings	permanent for the fixing, still needs the paint system

On price, this sits inside the preparation portion of an exterior repaint rather than as a separate line. Our published exterior range is $6,000 to $20,000 or more, with a typical three-bedroom house of around 150 square metres of floor area landing at $9,000 to $13,500 or more as at 2026, and labour running at around $50 an hour. Nail treatment is pure labour, and on a badly affected house it can take a full day per elevation, which is why a quote well below the others usually has no nail work in it. Our exterior painting quotes itemise preparation for that reason.

Can you do this yourself?

On a single-storey house within ladder reach, yes. It is slow repetitive work with simple tools: a nail punch, a hammer, a wire brush, filler and two small tins of primer. There is nothing technically difficult in it.

Two things should stop you. If the house was built in the 1980s or earlier the existing paint may contain lead, so have it tested. Dry sanding spreads that dust across your soil and into the house. Wet-scrape, sheet the ground, and leave the power sander in the shed. And if the affected boards are on a second storey or above a steep drop, access is the job rather than a detail of it. Scaffolding typically adds $1,500 to $4,000 or more depending on complexity and how long it stays up, which is not worth erecting for nail heads alone. That work belongs with a full repaint.

When is it fine to leave it?

If the timber is sound, the paint elsewhere has years left, and the staining is on an elevation nobody looks at, leaving it is a defensible decision. Rust stains are ugly long before they are structural.

The point where that stops being true is when the paint film is cracking open at each fixing and letting water into the board, because that is where rot begins. On the exposed southerly and westerly walls that transition happens faster, so check those two sides before deciding the whole house can wait.

If you are not sure which side of that line your house sits on, ask for a quote and we will tell you straight, including when the honest answer is to wait another two summers.