How often should sandstone be cleaned?
Most Sydney sandstone wants a gentle wash every one to three years. Shaded, south-facing or salt-exposed stone — near the coast, a pool, or under trees — sits at the one-year end; dry, sunny, sheltered stone can wait three. Leave it longer and lichen roots deeper and gets harder to lift. Gentle only: the NSW Heritage salt-attack guide warns aggressive cleaning drives salts in and spalls the stone.
The interval, set by shade and salt
Sandstone is not on a fixed calendar. The honest range is a gentle wash every one to three years, and where your stone lands depends on two things: how much sun it gets and how much salt reaches it. Dry, sun-baked, sheltered stone stays clean longer — three years between washes is fine. Shaded, damp, south-facing stone grows a green film fast and belongs at the one-year end. Walk the stone and read it. The face that never sees sun is the one that sets your schedule.
Salt is the other dial. Near the coast, beside a pool, or anywhere sea spray and mineral-laden water land on the stone, biological growth arrives sooner and the wash comes around more often. A sandstone wall in Vaucluse or Manly, a few streets from the water, works harder than the same wall in a dry inland pocket. So a Bronte forecourt and a leafy North Shore retaining wall can both be sandstone and still want cleaning on completely different clocks. Judge the wall in front of you, not the calendar.
Why waiting makes the job harder
The green and black growth on sandstone is not just dirt sitting on top. Lichen and moss put down structures that work into the pores of the stone, and the longer they sit, the deeper they anchor. Wash a wall that has been dirty for one wet season and the growth lifts cleanly. Leave the same wall for five years and the lichen has colonised the surface — patchy, stubborn, and unwilling to come off with a gentle method. That is the real cost of stretching the interval too far.
There is a candid limit worth stating. A clean lifts living growth and surface grime; it does not undo staining that has already migrated into the stone, and it will not reverse flaking where salt has already done its work. Cleaning on a sensible cycle is prevention — it stops the growth before it roots and stops the grime before it sets. Once sandstone has spalled or stained deep, no wash brings it back. That is exactly why the every-one-to-three-years habit beats a heroic rescue later.
Gentle wash only — the reason pressure backfires
The instinct with a dirty stone wall is to hit it with a pressure lance. On sandstone that is the wrong move, and the reason is chemistry rather than caution. The NSW Heritage salt-attack guide documents how soluble salts decay sandstone and masonry from within: water carries salt into the pores, it crystallises, and the pressure of those crystals breaks the stone apart grain by grain. Blast the surface with high-pressure water and you drive more salt deeper and strip the weathered skin that was protecting the stone underneath.
So the method matters more than the muscle. Sandstone gets a low-pressure, controlled wash with the right treatment to kill growth at the root, not a driveway lance turned on a heritage wall. The same guide warns against blasting affected stone for precisely this reason. Done gently and on schedule, a wash keeps the stone honest for decades. Done aggressively once, it can open the surface to the exact salt cycle you were trying to avoid. Slower is safer, and on sandstone, safer lasts longer.
Sealing: optional, breathable, and after the wash
A seal is the question everyone asks after the stone comes up clean. The honest answer: it is optional, and if you do it, it has to breathe. Sandstone holds and moves moisture through its pores; that is how salt gets out as well as in. A cheap film-forming sealer traps moisture and salt behind it, and the salt-attack guide is blunt that sealing affected stone can make the decay worse, not better. If the stone is already salt-damaged, sealing is the wrong call.
On sound, clean stone, a breathable penetrating seal can slow how fast grime and growth take hold, which stretches the interval between washes. It is a genuine option, not a requirement, and it always comes after the wash — never over dirty or damp stone. Treat it as a considered add-on for the right wall, not a default. The stone will tell you: if it is flaking or crusting with salt, clean gently and leave it to breathe rather than sealing the problem in.
Getting your number, and your schedule
Sandstone does not price like a window count. Size, growth, access, pitch and how much salt damage is already in play all move the job, so it is quoted per job rather than off a flat rate. The Schmick instant quote reads all of that against your address and returns a firm, bookable price in about 60 seconds — no site visit, and the figure holds unless the place is materially different from what the address suggests. You get a real number before you commit an afternoon to anyone's clipboard.
From there the schedule is simple. Book the first gentle wash, look at how quickly the growth returns, and set your interval — yearly for the shaded, coastal, salt-exposed walls, out to three years for the dry and sheltered ones. Pair it with a house soft wash on the same visit and the combined job runs cheaper than booking each apart. Get the exact number, then let the stone's own regrowth rate tell you when the next one is due.