The basic principle
Most cleaning methods rely on one thing: pressure, heat, or chemistry. TORC combines three inputs at low energy and lets the geometry of the tool do the work. Air, a small volume of water, and a fine inert aggregate are drawn together and delivered through a specially shaped nozzle that spins them into a vortex. The swirling motion means the aggregate strikes the surface at a shallow, glancing angle rather than head-on. It lifts the soiling and carries it away without driving into the stone beneath.
The system was developed by Stonehealth — the same manufacturer as the DOFF steam system — as an evolution of the older JOS process. The refinement is control. The vortex, the low air pressure, and the range of interchangeable nozzles let the operator calibrate the cleaning action precisely to the substrate and the soiling in front of them. That control is the whole point.
Air pressure: up to approximately 8 bar — a small fraction of the energy used in grit blasting. Water consumption: roughly 1.5 litres per minute, which suppresses dust and keeps the surface cool. Aggregate: a fine, soft, chemically inert powder. Nozzles: interchangeable, from broad panel work down to fine detail. No heat. No chemicals.
What it removes
TORC earns its place on the difficult soiling — the deposits that low-risk steam cleaning leaves behind. Understanding where it is the right tool, and where it is not, is the difference between a clean building and a damaged one.
It removes sulphate crusts effectively: the hard, dense, black-to-grey layer that builds up in sheltered recesses where rain never washes the surface. This is the soiling that defies steam, because it is not a loose deposit sitting on the stone — it is a crust chemically bound into the surface. It removes carbon deposits and general atmospheric blackening. It strips paint and limewash from masonry, including layered and historic coatings. It clears bitumen, limescale, and staining that will not respond to gentler methods. On brick, it lifts heavy soiling that would otherwise tempt a contractor towards acid.
What TORC is not is a default. It is an abrasive method, however gentle, and abrasion is never the first choice on a sound, lightly soiled surface. For biological growth — algae, lichen, moss — and for straightforward atmospheric soiling, steam is lower-risk and usually the correct call. TORC is specified when the soiling has earned it.
Why the vortex matters
The reason TORC can clean a sulphate crust without wrecking the stone comes down to angle and energy. Traditional grit blasting fires an abrasive straight at the surface at high pressure. It does not distinguish between the crust and the stone — it removes both, taking tooling marks, arrises, and carved detail with it. The damage is permanent and instantly recognisable: a flattened, sugary surface that has lost its worked character and will re-soil faster because it is now more porous.
The TORC vortex changes the physics. The aggregate arrives spinning, at low pressure, striking obliquely. It has enough energy to release a bound crust but not enough to erode the sound stone once the crust is gone. The soft, fine aggregate is doing gentle work, repeated and controlled, rather than one violent pass. In the right hands it stops at the boundary between soiling and substrate — which is exactly where cleaning should stop.
TORC is sometimes described loosely as “blasting”, and the word does it a disservice. Dry grit blasting and high-pressure sand blasting have no place on historic stone or soft brick. If a contractor proposes either on a period building, the correct response is to stop the conversation. TORC exists precisely because those methods cause the damage they claim to prevent.
The trial panel
No TORC work begins without a trial panel, and on a listed building the trial is a condition of consent, not a courtesy. A representative area of roughly one square metre is cleaned first, starting with the gentlest settings — the finest nozzle, the lowest effective pressure, the shortest dwell.
The panel is assessed against an uncleaned control area alongside it. The questions are simple and specific. Has the soiling lifted to an acceptable level? Is the stone surface beneath undisturbed — tooling marks intact, arris sharp, no sugaring? Has the aggregate found its way into open joints or fragile detail? On the basis of the answers, the nozzle, pressure, and aggregate flow are locked in for the full works, or adjusted, or — if the substrate is more vulnerable than it looked — another method is brought in. Nothing is scaled up on assumption.
When TORC is the right choice
TORC is the correct consideration when the soiling is stubborn and bound: sulphate crusts in sheltered recesses, cornice undersides, and reveals; heavy carbon staining that steam has not fully cleared; paint and limewash removal; and hard deposits on robust stone and brick. It suits Portland stone, most limestones and sandstones, granite, and harder brick. It comes into its own on the flat panel work and sheltered detail of civic and commercial facades — the parts of a London building that soil the worst.
It requires more caution, or an alternative, on very friable or delaminating stone, on soft or already-eroded surfaces, on fine terracotta and faience where the glaze is at risk, and on delicate carved detail where even gentle abrasion is a risk not worth taking. In those cases DOFF steam, a nebulous spray, or a poultice will usually be the safer specification. The judgement is made at the survey, on the material, not from a price list.
TORC and DOFF: two tools, one facade
TORC and DOFF are not rivals — they are complementary, and they are frequently used on the same building. A typical London facade carries two kinds of soiling at once: loose atmospheric blackening and biological growth on the rain-washed faces, and hard sulphate crust locked into the sheltered recesses. DOFF handles the first without touching the surface. TORC handles the second where steam alone would fail. Reading which soiling sits where, and specifying each method to the area it suits, is the skill that separates a considered restoration from a blunt one. For the full comparison, see our guide to DOFF vs TORC, and the detail on the steam method in what is DOFF cleaning.
Common questions
What is TORC cleaning?
TORC is a low-pressure cleaning system that combines air, a small volume of water, and a fine inert aggregate in a swirling vortex. The vortex lifts soiling from the surface with a gentle, controllable abrasive action. It removes sulphate crusts, carbon deposits, paint, and bitumen from stone and brick without heat or chemicals, and is widely accepted for use on listed buildings.
Is TORC cleaning abrasive?
TORC uses a very fine inert aggregate, so there is a controlled abrasive element — but it is a fraction of the energy of grit blasting. The air pressure is low (up to around 8 bar), the aggregate is soft and fine, and the nozzle size and distance are calibrated during a trial panel. Applied correctly, it removes the soiling without eroding the stone surface beneath.
What is the difference between DOFF and TORC?
DOFF cleans with superheated steam and works best on atmospheric soiling and biological growth. TORC cleans with a low-pressure vortex of air, water, and fine aggregate and works best on hard sulphate crusts and paint in sheltered areas that steam cannot shift. They are often used together on the same facade, each on the soiling it suits.
Is TORC cleaning approved for listed buildings?
TORC is one of the low-impact methods commonly accepted by conservation officers for listed building work, and it is used on cathedrals, churches, and monuments across the UK. As with any method, a method statement and trial panel are required, and written consent must be in place before full works begin.
If your building has soiling that has resisted gentler cleaning — a blackened cornice, a painted-over facade, a crust that will not shift — a site visit is the right starting point. We assess the substrate, identify the soiling type, and produce a written method statement before any commitment to works.
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