What paint does, and what it doesn't
The Building Code treats roof paint as a renewable protective coating, which only has to last at least 5 years. On metal, a good system holds rust back and buys the roof time. On tiles it's mostly looks: Monier says repainting concrete tiles doesn't improve waterproofing, and Resene says a leak keeps leaking if its source isn't fixed.
Resene's own advice is that a badly corroded roof is often better off with new sheets, or a new roof, than paint. Repaint or re-roof helps with that call.
What each roof needs
| Before the topcoat | Worth knowing | |
|---|---|---|
| Bare galvanised iron or ZINCALUME | Remove the form oil, then prime | Wattyl wants three coats for its 15-year guarantee; Dulux three on new surfaces |
| COLORSTEEL | A paint prep wash, then a pre-coated steel primer (Resene) | NZ Steel's warranty won't cover failures caused by the new paint |
| Concrete tiles | Clean, then a sealer to even out porosity (Resene) | Cosmetic only; Resene says a concrete stain is often the better choice |
| Decramastic | Moss treatment, spot priming, a textured coat where chips are gone | Brings back colour, not the chip texture; no water-blasting |
| Butynol and membranes | Moss treatment, wash, membrane roofing primer | Not usually painted, but it can be |
| Terracotta | Monier says it generally shouldn't be painted | Painted unglazed tiles need ongoing recoating |
| Asbestos cement | No water-blasting or aggressive cleaning | Resene recommends replacing or sheeting over instead |
Guarantees, and what they hang on
A paint guarantee covers the paint film, not the roof. Dulux guarantees Roof & Trim won't peel, flake or blister for 15 years on properly prepared metal roofs, and excludes concrete tiles. Wattyl gives Solagard Roof a 10 or 15 year guarantee depending on the surface and number of coats.
So ask which product, which primer and how many coats are being quoted, and get the guarantee conditions in writing. Following the maker's system to the letter matters more than the brand.
Weather, salt and geothermal air
Paint is fussy about conditions. Resene Summit Roof can't go on below 8°C, Dulux Roof & Trim not below 10°C, and Wattyl Solagard Roof only between 5°C and 35°C, with no rain or dew while it dries. Resene adds that a roof too hot to keep your hand on is too hot to paint.
Near the coast, Resene warns that salt settles on roofs quickly and surprisingly far inland, and recommends a freshwater wash every day before painting. It advises more than one primer coat near the sea, and Dulux recommends its metal primer especially in coastal or geothermal areas.
Rainwater tanks and old paint
If you collect drinking water, disconnect the tank before any washing or painting. Dulux says not to collect drinking water within 48 hours of painting, and Wattyl says wait until at least 10 to 15 mm of rain has rinsed the roof. Check the paint suits drinking water collection; Resene says Summit Roof does.
On older houses, Resene says roofs installed before 1971, or old coatings never stripped, should be tested for lead before preparation starts.
Safety on a painting job
WorkSafe treats roof painting that runs over several days as long-duration work, where scaffolding or edge protection should be considered, and says single-storey homes need the same fall protection as two-storey ones. A quote that never mentions edge protection is worth a question.
What to ask the painter
- Which product, primer and number of coats are you quoting?
- How will you prepare it, and will you test the old paint's adhesion?
- Is this system approved for my roof type and for drinking water?
- What edge protection or scaffolding is included?
Your jobs, and theirs
You can
- Disconnect rainwater tank inlets before work starts
- Note rust spots and peeling from the ground with binoculars
- Keep the guarantee and product details with your house papers
Leave to a roofer
- Moss treatment, washing and rust treatment
- Fixing loose fixings, flashings and rusted sheets first
- Priming and every coat of paint
Where we'd start
We'd have the roof checked before anyone paints it. If the metal is sound with only surface rust, a properly prepared and primed roof can buy years. Rust holes, loose sheets and leaks get fixed first or the paint is wasted, and if most of the roof looks like that, we'd put the money towards a re-roof instead.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.