Is it decramastic, or a newer pressed steel tile?
Gerard, which designs and makes pressed metal tiles in New Zealand, describes decramastic as an early stone-coated tile: galvanised steel with stone chip set into a bitumen coating. It has since been superseded by modern pressed steel tiles on a zinc-aluminium coated base, finished in textured chip or smooth satin paint.
From the street the old and new look alike. Gerard says tiles made in the late 1980s or later, with a plain painted surface or no scalloped edge, are less likely to be the early type. If you're not sure, a roofer can usually tell on the first visit.
How decramastic wears out
Resene explains it simply. The stone chips erode, exposing the black bitumen, then the galvanised steel, which eventually rusts. Sooner or later, Resene says, owners face a choice between painting and replacing.
Signs you can spot from the ground: patchy colour, bare dark areas, rust spots or streaks, moss and lichen, and gritty granules in the spouting (gutters). Gerard says white corrosion deposits spread over the roof usually mean a recoat is prudent.
Repair, recoat or re-roof?
| Repair | Recoat | Re-roof | |
|---|---|---|---|
| Suits | A few damaged, rusted or leaking tiles | Worn chip and white corrosion, steel still solid | Rust through across large parts of the roof |
| What's involved | Damaged tiles swapped once the cause is found | Gentle clean, spot priming, rebuilt texture, topcoats | New pressed steel tiles or longrun, sometimes laid over the old tiles |
| Asbestos test | Before tiles are cut or lifted | Before cleaning starts, or treat it as asbestos | Before removal |
| Building consent | Usually not needed for like-for-like repairs | Usually not needed | Often needed if the roofing system changes |
| Who to look for | A roofer who works on metal tiles | A contractor who has recoated decramastic before | A roofer, and an LBP where the work needs consent |
Test for asbestos before anyone disturbs old tiles
Gerard says metal tiles made before the early 1980s often had small amounts of asbestos in the bitumen or mastic coating, and some went on as late as 1982. Resene names Decramastic as a profile likely to contain it. You can't tell by looking, so have a sample tested or treat the roof as asbestos: no water-blasting, sanding or cutting. WorkSafe's guidance for weathered decramastic is a biocide from a low-pressure sprayer, with the surface kept wet. Here's how to check for asbestos.
What makes the job bigger or smaller
How far the rust has got. A faded roof with a few rusty tiles is a small job. Rust on tile after tile turns a repair into a recoat, and a recoat into a re-roof. Steeper and higher roofs take longer to make safe, since WorkSafe's example control for roofing work on a house is scaffolding with full edge protection.
Whether asbestos is confirmed. Once more than 10 square metres of asbestos-containing tiles are coming off, the work needs a licensed asbestos removalist. Gerard says its Concealed Fastening Shake tile can be laid straight over existing decramastic, leaving the old tiles undisturbed. Ask your roofer whether that suits your roof and whether it needs a building consent.
Where you live. BRANZ gives Gerard's tile systems a minimum expected life, with cleaning and recoating, of 40 years in NZS 3604 exposure Zone B, 30 in Zone C and 20 in Zone D. Zone D takes in land within 500 m of the coast, so have your roofer confirm your zone before choosing a new tile or coating.
What a good decramastic quote spells out
- Whether the tiles have been tested for asbestos, and how the work changes if they haven't
- Which tiles are being replaced, roughly how many, and what with
- For a recoat, the coating system by product name and the number of coats
- How the crew will move on the tiles, and who covers any they dent
- Scaffolding or edge protection, since WorkSafe treats roof work over several days as long-duration work
- For a re-roof, whether consent is needed, who applies, and which LBP will do or supervise the work
- A quote (a firm price) rather than an estimate, and the workmanship and maker's warranties
What you can check, and what to leave to a roofer
You can
- Look from the ground or an upstairs window, ideally with binoculars, for bare patches, rust and white powdery deposits
- If you're comfortable on a ladder, look into the spouting for a build-up of stone granules, without stepping onto the tiles
- Note where ceiling stains show and what kind of weather brings them on
- Find out roughly when the roof went on, from the council property file or old paperwork
Leave to a roofer
- Any walking on the tiles: one wrong step dents them
- Swapping tiles, ridge pieces or flashings
- Cleaning and recoating
- Anything involving tiles that might contain asbestos
What we'd do with an old decramastic roof
Answer the asbestos question first, because it shapes every option. Then ask a roofer to photograph the worst areas and tell you plainly whether the steel under the chip is still sound. If it is, we'd repair the damaged tiles and recoat, and get more years out of the roof. If rust has come through across big parts of it, we'd skip the paint and put that money towards a re-roof. When you're ready, we can pass the job to one checked roofer who knows metal tiles.
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.