Sandstone · North Shore
Sandstone cleaning and sealing, North Shore
Soft wash cleaning and penetrating sealing for sandstone walls, paths, steps and frontages in Castlecrag, Northbridge, Mosman, Cremorne, Seaforth, Lane Cove, Hunters Hill and Killara. Owner-operated: Peter does the work himself.
Typical pricing from $1,800 · most whole-frontage jobs $3,000–$4,500 · usually two visits · $20M public liability
Why sandstone greys and blackens
Sandstone is sand grains held together with gaps between them. That open structure is why it looks so good, and it is also why it stains: it soaks up water, and the water carries everything else in with it.
On the North Shore the usual causes are moss, algae and lichen on shaded and south-facing walls, tannin from leaf litter under big trees (the brown-grey tide marks along paths and steps), and salt from harbour air that can crystallise just under the surface. The black film on a frontage is typically mould and algae, and it comes back fastest on stone that stays damp.
None of that is dirt sitting on top. It is in the pores, which is why a quick blast with a pressure washer gives a pale, patchy result that greys off again.
Soft wash, not high pressure
Sandstone is a soft stone. High pressure strips the face off the grains and leaves a rough, pitted surface that holds more dirt and greys faster than it did before. We clean sandstone with a soft wash: the right cleaner applied at low pressure, time to work on the growth at its roots, then a gentle rinse.
Before anything goes on a wall or path we run a test patch somewhere out of sight and let it dry. You see how the stone responds before we commit to the whole job, and we tell you honestly what it is likely to give back. Deep tannin staining and old iron marks can lighten rather than disappear.
How a sandstone clean and seal runs
1. Look, then test patch
We check the stone, how much shade and moisture it lives with, and what has already been put on it. Then the test patch, so the method is matched to the surface.
2. Soft wash the lot
Walls, paths, steps, balconies and the council strip out the front. Moss, algae and lichen are treated rather than blasted off, because growth left in the pores comes straight back.
3. Let it dry
Sealer will not penetrate damp stone, so the sandstone has to dry between the clean and the seal. That is why this is normally two visits. On the Castlecrag frontage below, the clean and the seal were done on consecutive days.
4. Seal with a penetrating sealer
We use SiF penetrating sealers: Australian-made, water-based, breathable and non-film-forming. On sandstone walls, paths and steps that is a silane-siloxane sealer where water repellence is the priority. It sits inside the stone, so the natural look and texture stay and there is no film to peel or go cloudy. A colour-enhancing finish that deepens the tone is available if you want it; the standard finish is deliberately invisible.
5. The bits people forget
The council driveway and footpath strip, steps, retaining walls and the sandstone around the entry. They are in the quote unless you ask us to leave them out, so the front does not end up half done.
What does not get sealed
Not every wall needs sealing. Rock and retaining walls in deep shade that stay wet from behind are often better soft washed and left alone. On a Newport job we soft washed the sandstone rock wall and retaining wall to remove moss and algae and did not seal them, while the travertine on the same property was cleaned and sealed. The quote tells you which surfaces get which treatment and why.
Recent sandstone work
Castlecrag: sandstone frontage
Entrance path, balconies, driveway and the council driveway and walkway, cleaned and sealed over two consecutive days. A repeat client: we had already cleaned inside the same property.
Fairlight: sandstone walls on a two-level exterior clean
The sandstone walls were chemically treated to remove and inhibit mould, moss and algae growth, alongside a soft wash and pressure wash of the driveway, walkways, balconies, stairs and courtyards.
Newport: rock and retaining walls
Sandstone rock wall and retaining wall soft washed for moss and algae, with the exterior stone stairs cleaned. These walls were cleaned and left unsealed.
Where we do it
We clean and seal sandstone across the North Shore: Castlecrag, Northbridge, Mosman, Cremorne, Seaforth, Lane Cove, Hunters Hill and Killara, as well as the Northern Beaches and Eastern Suburbs. If you are not sure the stone in front of you is sandstone, send a photo in daylight. It is usually obvious from one clear picture.
What it costs
Clean and seal is priced on area, condition and which sealer the surface needs, not on a flat rate per square metre. A shaded path thick with lichen is a different job from a clean surface that just needs protecting.
As a guide: smaller jobs start from $1,800. Most whole-frontage jobs (path, driveway, balconies, council strip) land between $3,000 and $4,500. It is usually two visits, because the stone has to dry before it is sealed.
Sandstone paths and steps on their own sit at the smaller end. Whole sandstone frontages, with the driveway and council strip, sit in the middle of the range.
You get a quote inside 24 hours, from photos or a site visit.
Common questions
Will soft washing damage soft sandstone?
Soft washing is the low-pressure method we use because high pressure is what damages soft sandstone. We also test the cleaner on a small, out-of-sight patch first and let it dry, so you see the result before we do the rest.
Can you get the black stains and moss off my sandstone walls?
The growth itself usually comes off. Deep tannin or iron staining may lighten rather than disappear completely, and we will tell you what to expect after the test patch rather than before it.
Does sealing sandstone change how it looks?
The standard finish does not. A penetrating sealer soaks into the stone rather than sitting on it, so the stone keeps its natural texture and matt look. A colour-enhancing finish that deepens the tone is available as an option.
Do you do the council strip out the front?
Yes, and we would normally recommend it. It is the first thing seen from the street and the part most quotes leave out. It is included in our quotes unless you ask us to leave it.
Why does it take two visits?
Sealer will not penetrate damp stone, so the sandstone has to dry between the clean and the seal. Depending on weather and shade, that usually means returning the next day or once it has dried.
Related
Travertine and pool decks, Northern Beaches
Neutral-pH clean and penetrating seal for travertine and limestone.
Driveways and council crossings, Sydney
Degrease, clean and seal aggregate, pavers and stone driveways.
All stone cleaning & sealing
How we clean and seal, what it costs and what we do.