When is a decramastic roof worth painting?
Good candidates have faded or patchy colour, bare black bitumen where chip has gone, and white powdery corrosion, which Gerard says usually means a recoat is prudent.
Poor candidates have rust holes or leaks in several places. Resene's roofing guide says a badly corroded roof is often better replaced, in whole or in part, than painted. Rusted-through tiles need repairing before any coat goes on.
Newer satin-finish pressed steel tiles are different. Gerard's warranty expects them to be repainted after 15 years, or 10 in severe marine areas, so that repaint is maintenance rather than rescue.
How a decramastic repaint is done
Treat and wash
Moss and mould are treated and the roof washed down gently. Resene says water-blasting dislodges the chip, and WorkSafe's guidance for weathered decramastic is biocide from a low-pressure sprayer, with the surface kept wet.
Spot prime the bare areas
Bare galvanised steel and big patches of exposed bitumen each get their own primer: Galvo-Prime and Membrane Roofing Primer in Resene's system.
Build back the texture
A coarse textured coating, Resitex Coarse in Resene's case, is brushed onto eroded areas so bald patches don't stand out.
Two sprayed topcoats
Two coats of Lumbersider, which Resene says need spraying for a reasonable finish, leading edge of each tile first.
Asbestos and lead: test before any preparation
Decramastic laid before the early 1980s may have asbestos in its coating. Resene also says roofs installed before 1971, and older roofs whose early coatings were never stripped, should be tested for lead. If either turns up, preparation must follow the safety rules for that material. Never scrape, sand or water-blast an old decramastic roof yourself.
Weather, tank water and safety on the day
Roof paint needs mild, dry weather. Dulux, for one, says not to apply its roof paint below 10°C, and that rain, frost or dew while it dries will damage the film.
On tank water? Dulux's advice is to disconnect tank inlets, hose the roof down afterwards and not collect drinking water within 48 hours. Ask what your painter's paint maker says.
WorkSafe treats roof painting over several days as long-duration work, where scaffolding or edge protection should be considered, so expect the quote to cover it.
Questions to ask the painter or roofer
- Have you repainted decramastic before, and can I see one?
- Will you test for asbestos and lead, or work as if both are there?
- How will you clean the tiles without a high-pressure water-blaster?
- Which primers and topcoats will you use, by name, and how many coats?
- Is this a quote (a firm price) or an estimate, and what's the warranty on paint and workmanship?
Leave the brush on the ground
You can
- Check colour and chip loss from the ground with binoculars
- Look at a neighbour's repainted decramastic to see the finish
- Plan how you'll manage a rainwater tank during the job
- Move cars and pot plants away from the eaves
Leave to a roofer
- Cleaning, priming and spraying
- Asbestos and lead testing
- Replacing rusted tiles first
- Scaffolding and edge protection
What we'd sort out before any paint is bought
Get the asbestos and lead answers first, then have any rusted-through tiles replaced before a single coat goes on, because paint over a hole is wasted. If the steel is sound, a proper repaint by someone who has done decramastic before is money well spent. If they keep finding rust, we'd put that money into 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.