Stone cladding is everywhere on newer Sydney builds — entry walls, feature panels, pool pavilions, fence returns. It reads as solid stone and it is not. It is a thin veneer, typically 15 to 30mm, adhered to a substrate with a bonding mortar.
That construction is the whole reason it needs care.
Why pressure is a problem
A cladding panel is held on by adhesive and by its jointing. High pressure directed at a joint pushes water straight behind the stone, where it has no easy way out.
Water behind cladding does three things. It degrades the adhesive bond over time. It carries salts that crystallise in the bedding mortar. And in a freeze or a strong wetting-drying cycle it works the panel loose.
The symptom is drumminess — tap across the wall and some panels sound hollow. Those have debonded. A pressure washer will take them off, and a stone panel falling from an entry wall is a safety issue as well as an expensive one.
Tap the wall before anyone cleans it. Same test as cracked render.
What stone you have
It matters, because the chemistry differs.
Sandstone and limestone cladding is calcium carbonate or carbonate-cemented. No acid, ever. Acid etches the face and dissolves the cement holding the grains together — the limestone argument applies identically.
Travertine cladding, common on pool pavilions. Same rules, plus open voids that hold growth — here.
Granite and basalt are harder and tolerate more, though acid still dulls the finish and basalt has its own iron spotting problem — covered here.
Slate delaminates in sheets if worked too hard.
Reconstituted or cast stone is cement-based with a coloured face. Pressure removes the face and the colour with it.
The right method
- Tap the whole wall and mark anything drummy. Do not clean those areas; report them.
- Check the joints. Open or missing pointing is a direct water path.
- Wet the wall down with plain water first.
- Apply a pH-neutral stone cleaner, or dilute sodium hypochlorite where the problem is organic growth.
- Agitate with a soft brush, working panel by panel.
- Rinse at low pressure, with the lance angled downward and across the joints, never up into them.
- Let it dry fully before considering any sealer.
Angling matters more here than on almost any other surface. Water driven upward goes under the top edge of a panel and stays there.
Common problems
White bloom in the joints. Efflorescence from the bedding mortar. Brush off dry; wetting recycles it back in. Recurring bloom means water is getting in behind — the mechanism.
Dark biological staining on shaded elevations. Hypochlorite, dwell, rinse gently.
Rust spotting on basalt or sandstone with iron content. Not surface staining and not removable by cleaning.
Mortar smear from installation. Common on new work, and the temptation is acid. On carbonate stone that is how walls get ruined — see builders clean after a renovation.
Sealing
Worth doing on porous cladding, and the usual rule applies: breathable impregnating sealers only. A film traps moisture behind the stone, which is precisely the failure mode you are trying to avoid.
The product logic is the same as sandstone sealer.
Seal the joints too — open pointing is where most of the water enters.
Where it tends to fail
Cladding below ground level or behind a garden bed, where it wicks moisture from the soil. Cladding with no flashing above it. Cladding on a wall with a drainage problem.
In all three cases cleaning is cosmetic and the water needs addressing first.
For a professional clean and an honest assessment of whether the panels are sound, see stone cleaning.
