Can a decramastic roof be painted, or does it need replacing?

Yes, a decramastic roof can be painted, and on a roof where the steel underneath is still sound it is a legitimate way to get more years out of it. If the tiles are rusting through, cracked, leaking or lifting, paint will not fix that, and the honest answer is repairs or replacement.

What decides it is not how bad the roof looks from the street. It is the condition of the steel under the stone chip.

What is a decramastic roof actually made of?

Decramastic tiles are the pressed metal tiles with a gritty, stony surface found on a lot of New Zealand homes. Resene's roof painting guide describes them as pressed galvanised iron with a bitumen basecoat applied over it, and stone chips embedded in the bitumen.

That layering explains how they age. Resene sets out the sequence: over time the stone chips erode, exposing the bitumen, and eventually the galvanised iron, which will ultimately rust. So a decramastic roof goes through three stages:

1. Chip still mostly intact. The roof looks dull, faded or mossy, but the protective layers are doing their job.
2. Chip worn away in patches. Dark, smooth bitumen shows through, usually worst on the most exposed faces and where water runs off.
3. Steel exposed. Bare galvanised patches, then rust, then eventually rust holes.

Painting makes the most sense in the first two stages. By the third it depends on how far the rust has gone.

When is coating a decramastic roof sensible?

When the roof is watertight, the tiles are sitting properly and the problem is mostly cosmetic or early wear. In that situation a coating system does two things: it puts colour back, and it adds a protective layer over areas where the chip and bitumen have started to go.

Resene is fairly matter-of-fact about it. Its guide says painting decramastic is relatively straightforward, but the topcoats will need to be sprayed if a reasonable finish is to be achieved. The system it generally recommends is:

• Treat for moss and mould and wash the roof down thoroughly.
• Spot prime bare galvanising with a waterborne primer. Resene notes that a solventborne galvanised primer would perform better on aged iron, but it also softens the remaining bitumen, which the waterborne one does not.
• Spot prime any large areas of bare bitumen with a primer made for membrane roofing.
• Brush a coarse textured coating onto areas where the stone chips have eroded. Resene's own words are that this is "not perfect" but helps make good the tiles.
• Spray two topcoats, in a lower gloss finish, which Resene says helps disguise patchiness, painting the leading edge of each tile first.

Notice how much of that is about bare spots and patchiness. That is the reality of these roofs. A painted decramastic roof looks tidy and uniform from the ground, but close up it is still a textured roof with repaired patches, not a new one.

What signs mean it is past coating?

Paint sits on top of what is there. It does not make rusted steel strong again, it does not reseat a loose tile and it does not stop a leak at a flashing. These are the signs that a coating on its own is the wrong answer:

What you see	What it usually means	Coating on its own?
Faded colour, moss, dull chip, few bare spots	Surface wear only	Usually a good candidate
Patches of smooth black bitumen showing	Chip eroded, steel still covered	Often fine, with the extra priming and texture steps
Bare grey galvanised steel on tile faces	Protective layers gone in places	Possible if caught early, needs priming first
Rust staining, flaking rust, soft or pitted steel	Corrosion under way	Only if a roofer confirms the steel is sound
Rust holes, light through the roof space, leaks	Tiles have failed	No. Tiles need replacing first
Loose, lifted or cracked tiles, sagging sections	Fixing or structural problem	No. Roofing repair first

If you are unsure which row you are in, the most useful thing you can do is look from inside the roof space on a sunny day. Pinpricks of daylight or water stains on the underside of the tiles or the timber tell you more than the view from the lawn. How to judge the rust side of it is covered in more detail in when a roof is too rusty to paint.

What are the honest limits of painting one?

• It is not a new roof. A coating protects the tiles that are there. Tiles near the end of their life will still reach it.
• Preparation can damage the chip. Washing and walking on an old decramastic roof loosens chip that is already barely hanging on, which is why the washdown needs care and why whoever does it needs to know where to step.
• It will look textured and slightly uneven. Resene points out that its recommended lower gloss topcoat helps disguise patchiness. Expect a tidy result, not a factory one.
• It is not a DIY job. Spraying topcoats on a pitched roof is work for someone with the equipment and fall protection. The height and the fragile surface make this one to leave alone.

Resene also mentions that some companies market themselves as decramastic "reinstaters", and says there is nothing inherently special about their service or products. They have simply specialised. That is useful to know when you are comparing quotes that use different language for the same work.

So should you paint it or replace it?

If the roof is sound and watertight and you want it to look right and hold on for a good while longer, painting is a sensible spend. If the roof is leaking, rusting through or moving, the money is better put toward replacement, and painting first just delays that decision while costing you twice.

The wider trade-off, including when replacement is the better long-term buy, is laid out in roof painting vs replacement. On exposed Wellington sites, one face of a roof is often in noticeably worse shape than the rest, much as south and west walls weather faster than sheltered ones, so it should be checked face by face rather than judged from one corner.

What should a quote for painting one include?

It should say how the roof will be washed, how bare steel and bare bitumen will be treated, whether eroded chip areas get a texture coat, how many topcoats will go on and how they will be applied. If a quote just says "wash and two coats", ask about the rest. You can see what we look for on a roof on our roof painting page.

If you would like a second opinion before you commit either way, ask us to come and look at yours.