Mine Subsidence, Salt Air and Concrete in Newcastle

Is your block in a mine subsidence district?

Newcastle was built on coal, and some of it came out from under the suburbs. City of Newcastle's development control plan says parts of the council area sit over old underground coal workings, or close enough to be affected by them. Where there's a risk the ground could move, a mine subsidence district is declared. Subsidence Advisory NSW lists Newcastle and Lake Macquarie among them.

Checking takes a couple of minutes. Search your address on the NSW Planning Portal Spatial Viewer. If the block's in a district, the search results show which surface development guideline applies, under the heading Mine Subsidence Development. Write the guideline number down. You'll need it.

Do you need approval to pour a driveway or a slab there?

In a district, Subsidence Advisory NSW says you must get its approval before starting work when you build or subdivide. Some minor works are exempt, and the agency's exempt development list, dated April 2023, says which. These are the lines that matter for concrete.

Work	Size limit	Exempt under
Driveways and hard stand spaces	None listed	All guidelines except 4 and 5
Demolition	None listed	All guidelines
Patios	50 square metres	All guidelines except 1, 1A and 7
Carports	50 square metres	All guidelines except 7
Garages	50 square metres, no services or utilities	All guidelines except 1, 1A and 7
Retaining walls	1 metre high	All guidelines

So unless your block is under Guideline 4 or 5, a driveway or a hard stand doesn't need Subsidence Advisory approval. Breaking out old concrete doesn't need it under any guideline. Anything that isn't on the list needs approval before work starts.

One thing to keep straight. The exemption is only about subsidence. Council rules still apply, including council approval for the crossover.

What if you think the ground has already moved?

Cracks have plenty of ordinary causes, and most have nothing to do with mining. If you're in a district and the damage looks like the ground itself has shifted, ask Subsidence Advisory NSW before you spend money on repairs. A repair contractor can fix concrete. They can't tell you what an old mine is doing underneath it.

What do acid sulfate soils do to concrete?

Left alone, nothing. City of Newcastle's page on acid sulfate soils says they're harmless while they're undisturbed. Dig them up or drain them and the sulfides in the soil react with the air to make sulfuric acid, which the council says can corrode concrete and steel.

They're found in low-lying coastal areas, generally where the ground is less than five metres above sea level. The council's maps sort affected land into five classes. Class 1 is the highest risk, where any works count. In the other classes it depends how deep you dig or how far the water table drops. The council counts footings and foundations as works, along with moving more than a tonne of soil.

We're not naming suburbs, because the council's page doesn't. If your block is low and near the harbour, the river or a creek, ask the council which class it's in before anyone excavates. A driveway on a shallow base is a different thing to deep footings. Still the council's call, not ours and not the concreter's.

What does salt air do?

Concrete near the coast gets salt on it, and the salt works its way in to the steel. Steel rusts, rust takes up more room than steel did, and the concrete over it cracks and breaks away. That's spalling, or concrete cancer. Rust stains are the early sign.

How close is too close? We couldn't confirm a distance from an official source we could open, so we're not quoting one. Tell us how far you are from the beach or the harbour. The concreter, or an engineer on a bigger job, picks the concrete strength and how deep the steel sits to suit.

And the rain?

Low ground is also where the water ends up. The Bureau of Meteorology's Newcastle Nobbys station averages about 1,120 mm of rain a year, with March to June the wettest months. On a flat or low block, where a driveway or slab sends that water matters as much as the concrete. Ask how the falls and the drainage will work.

What should you do before you ask for a quote?

Search your address on the Spatial Viewer and note any mine subsidence guideline.
If the block's low-lying, ask the council about its acid sulfate soils class.
Work out roughly how far you are from salt water.
Put all three in your enquiry. It changes who we send and what they quote.

Planning a new driveway? See concrete driveways. Rust stains or concrete breaking away? That's concrete repairs. Not sure whether your suburb's covered? Check the areas we cover.

Sources

These are independent sites. We are not affiliated with or endorsed by them. Each was checked in November 2026.

Old Mines, Salt Air and Low Ground: What Newcastle Blocks Do to Concrete