Do I need council approval to clean heritage sandstone?

It depends on your council and the work. Under clause 5.10 of the local LEP, councils can confirm in writing that minor works or maintenance do not need consent. Some, like Woollahra, require that confirmation before work starts. Gentle cleaning is low-impact, but restoration, repointing, coating removal or sealing are more likely to need it, so check first.

Can heritage sandstone be pressure washed?

Not with a household pressure washer and a narrow tip, which erodes the stone and strips its weathered skin. A specialist may use a wide, controlled low-pressure rinse on sound stone after testing, but never on fretting stone or soft lime joints.

Should heritage sandstone be sealed after cleaning?

Often not. Many heritage walls are better left unsealed so moisture and salts can escape. Water-repellent coatings on salt-affected or damp walls can trap salts behind the treated layer and cause spalling. If a sealer is proposed, it should be breathable and justified for that location.

What is the safest way to clean old sandstone?

Start with the gentlest method: dry brushing, then water and a natural-bristle brush on a trial area. Judge the result once the stone is dry. Biocides suit mould and lichen, and poultices suit specific stains. Acid, abrasive blasting and high pressure should be ruled out.

Why is cement mortar bad for sandstone walls?

Cement mortar is harder and less permeable than sandstone. Moisture and salts are then forced through the stone instead of the joint, so the stone erodes around the mortar. Lime mortar is softer and breathable, so the joint wears first and can be renewed.

How long does a heritage sandstone clean take?

Longer than a standard clean. Allow time for the trial, for drying before it is assessed, for biocides to work and for any poultices to dry, which can take days or weeks. Any council confirmation also needs to be in hand before work starts.

Heritage Sandstone Cleaning in Sydney: A Guide

The Prestige Standard stone-care team · Published 5 November 2026 · Updated 5 November 2026 · 8 min read

Heritage sandstone cleaning in Sydney: doing it the conservation way — Illustrative image.

Why heritage sandstone needs a different approach

Much of Sydney's older housing stock, from Paddington terraces to Vaucluse villas and Manly cottages, is built from or trimmed with Hawkesbury sandstone. Many of these homes are heritage items or sit inside heritage conservation areas. The stone on them has often weathered for well over a century, and it carries evidence of that history: tooling marks, a firmer weathered skin, softened arrises and a colour that cannot be recreated.

That weathered skin matters. Beneath it, old sandstone can be considerably weaker than it looks. Cleaning that removes the skin leaves a softer, more absorbent face that soils faster, grows mould sooner and erodes more quickly. It also removes part of what makes the building significant. Heritage cleaning guidance is written around that risk, and it is why the right method on a heritage wall is usually slower and gentler than many owners expect.

It also helps to be clear about why you are cleaning. Removing soiling that is actively harming the stone, such as biological growth that holds moisture, or deposits that hide cracks needing repair, is a sound reason. Cleaning purely for a bright, uniform look is where over-cleaning begins.

The conservation principles

Australian heritage practice is guided by the Burra Charter, published by Australia ICOMOS. Several of its principles translate directly into how stone should be cleaned.

A cautious approach. The Charter asks practitioners to change as much as necessary but as little as possible. For cleaning, that means removing the harmful soiling, not every trace of age.
Traditional techniques and materials first. The Charter prefers traditional techniques and materials for significant fabric, with modern methods used where there is firm evidence or experience behind them.
Maintenance is protective care. The Charter defines maintenance as the continuous protective care of a place. Regular, gentle care is the goal, rather than an aggressive clean every few decades.
Reversibility. Treatments that cannot be undone, such as many sealers and hard repairs, deserve particular caution.

In practice, this is also the most economical approach over the life of a building. A gentle clean that needs repeating in a few years usually costs the stone nothing, while one aggressive clean can remove surface that took a century to form and cannot be put back.

Two working rules follow from these principles and appear in almost every piece of cleaning guidance:

Use the gentlest method that works. Start with water and a soft or natural-bristle brush. Move to anything stronger only if that fails, and only one step at a time.

Test first. Trial the method on a representative area beside an uncleaned patch and judge it only once the stone has fully dried. Where time allows, let the trial weather for a while before committing, because some damage, including salt-related fretting, does not appear straight away.

What Heritage NSW guidance says

Heritage NSW publishes a series of heritage maintenance information sheets, including Cleaning masonry walls (information sheet 6.1), which covers stone, face brick and unpainted render. Heritage Victoria later adapted the same Heritage Council of NSW material into its own guide to cleaning masonry. The key points for sandstone are consistent:

Over-cleaning is a common problem. Define what you are trying to remove before choosing a method.
Water is the simplest and safest starting point, with a firm natural-bristle brush, moving from cold to warm water only if needed.
Trial areas of about one to two square metres, next to an identical uncleaned area, so the result can be judged fairly. The guide notes that small trials can look better than a full wall, so expect some variation.
Pressure must be controlled. A wide, medium-pressure fan can be acceptable on sound stone, but the guide warns that softer materials, including mortar joints, can be damaged even at lower settings.
Mineral acids are not recommended for sandstone. They can bleach the stone, cause uneven iron staining, weaken it over time and leave salts behind in the pores.
Grit blasting is generally avoided on old sandstone and its soft mortar.
Choose on skill, not price. The guide cautions against simply taking the lowest quote, because careless methods cause irreversible damage.

The companion NSW guide Salt Attack and Rising Damp adds three warnings directly relevant to cleaning and repair: some cleaning compounds introduce salts into walls; hard cement mortar should not be used to repoint lime-mortar joints; and water-repellent coatings on salt-affected walls risk trapping moisture and salts. For major public buildings, the NSW Government's Heritage Stoneworks team applies similar principles, retaining original stone where possible and replacing it only where it has deteriorated beyond repair.

Council approval and clause 5.10

Much of the Eastern Suburbs sandstone is heritage-listed or sits in a heritage conservation area. Paddington, Woollahra and Watsons Bay are examples, along with smaller areas in Vaucluse, Bellevue Hill, Rose Bay, Darling Point, Double Bay, Bronte, Coogee, Randwick and Manly.

Under clause 5.10 of each council's Local Environmental Plan, work to a heritage item or in a conservation area generally needs development consent. Councils can, however, confirm in writing that minor works or maintenance do not need consent, as long as the work will not harm the heritage significance.

Woollahra Council, for example, asks owners to notify it and receive written confirmation before work starts. Its examples of possible minor works include repointing sandstone in the traditional manner with traditional materials, and it excludes painting stonework. Woollahra defines maintenance as ongoing protective care that does not remove or disturb existing fabric or introduce new materials. Items on the State Heritage Register can need separate approval under the Heritage Act.

Gentle cleaning is the least invasive work there is, but councils differ in how they treat it. For heritage-listed homes and conservation areas, especially where restoration, repointing, coating removal or a new sealer is involved, check with your council first. A written scope of work and method statement makes that conversation much easier. Our regulations page summarises the rules and links to the sources.

What to avoid on heritage sandstone

Most of the damage we see on heritage stone was done by well-meant cleaning or repair. These are the main things to rule out.

Acid and brick cleaners. Hydrochloric acid and similar products attack the binder, release iron as orange-brown blooms and leave salts in the stone.
High pressure. A narrow or turbo jet cuts into the stone and strips the weathered skin, leaving pale stripes and a sanded texture that soils faster. It also blows out soft lime mortar.
Abrasive blasting and wire brushes. Both remove surface stone and detail, and steel wire can leave fragments that later rust.
Bleach and salt-forming cleaners. These can add sodium salts to a porous stone that may already be salt-affected.
Sealing that traps moisture. Film-forming coatings and many water repellents can hold moisture and salt inside the wall. Salt then crystallises behind the treated layer, and the face can spall. Research at UTS on Sydney sandstone noted that waterproof polymers used overseas have sometimes made decay worse.
Cement repointing and hard patching. Cement mortar is harder and less permeable than the stone, so moisture and salt are forced through the stone instead of the joint, and the stone erodes around it. Lime mortar is designed to be the sacrificial element.
Painting stonework. Woollahra's guidance excludes painting stone from minor works, and paint can also act as a seal that stops walls drying.

Cleaning methods on heritage sandstone, from gentlest to most aggressive
Method	Suitability on heritage sandstone	Notes
Dry brushing with a soft or natural-bristle brush	Suitable	Good first step for loose dirt and surface salt
Water and a natural-bristle brush	Suitable	Start cold, move to warm only if needed
Stone-safe biocide left to dwell	Usually suitable after testing	For mould, algae and lichen; growth weathers away
Poultices	Suitable for specific stains and salts	Draws material out rather than scrubbing the face
Controlled low-pressure or warm water rinse	Specialist use on sound stone only	Wide fan, held back; never on fretting stone or soft joints
Household pressure washer with narrow tip	Not suitable	Permanent erosion and loss of the weathered skin
Mineral acids and brick cleaners	Not suitable	Iron staining, binder loss and salts left behind
Grit or sand blasting	Not suitable	Removes surface stone and detail

How to brief a contractor

A clear brief protects the stone, keeps the council conversation simple and makes quotes comparable. Before work starts, ask for, or agree on, the following.

Heritage status. Tell the contractor whether the property is a heritage item, in a conservation area or on the State Heritage Register, and who will contact the council.
A defined goal. Say what is to be removed (for example, black growth on the south wall and steps) and what is to stay, such as patina and tooling marks.
A written method statement. It should name the cleaning method, the products with their safety data sheets, dilutions, dwell times and any pressure limits.
A trial area first. Agree where it will be, how big it is, and that you will review it dry before the main works.
Exclusions in writing. No acid, no high pressure, no abrasive blasting, no cement mortar and no sealer without your separate approval.
Repointing and repairs. If any are proposed, ask for lime-based mortar matched to the existing, and confirm whether council confirmation is needed first.
Sealing. If a sealer is proposed, ask why, which product, whether it is breathable, and how it would be removed or renewed later. On many heritage walls the right answer is no sealer.
Run-off and site care. Wash water must not enter stormwater drains. Ask how drains will be bunded and water recovered.
Insurance, licensing and a record. Ask for insurance details, check licensing for larger jobs (our regulations page explains the threshold), and ask for before-and-after photos and a record of the products used.

What you can do yourself

Owners can do a lot to reduce how often heritage stone needs professional cleaning, and almost all of it is about moisture.

Keep gutters, downpipes and stormwater pits clear so walls are not soaked during rain.
Move garden beds, mulch and sprinklers away from the base of walls, and keep fertiliser off the stone.
Trim plants that keep walls permanently shaded and damp.
Sweep leaves off steps and paving before they stain.
On sound, low-level stone, gentle cleaning with water and a soft brush is fine. Leave fragile, flaking, carved or high areas alone.
Photograph the stone each year so changes are easy to see.

Our guides to how to clean sandstone and removing black mould from sandstone cover safe DIY methods in more detail.

When to call a specialist

Call a specialist when the stone is fretting, flaking or powdering; when there is rust, paint, graffiti or an old coating to remove; when salts keep returning; when joints are failing or have been repointed in cement; or when the work is large, high or on a prominent facade. Those jobs need experience, the right equipment and a method that will stand up to council scrutiny.

Our sandstone cleaning service starts with a test patch and uses low-impact, conservation-led methods with full run-off recovery. Where the problem is inside the stone, sandstone restoration and stain removal cover poultices, coating removal and lime-mortar joint repair. We work across the Eastern Suburbs and Northern Beaches, and we supply a written scope and method for your council. Structural problems need an engineer and a stonemason, and we will tell you if we see them. Contact us to arrange an inspection.

Heritage sandstone cleaning in Sydney: doing it the conservation way