A swirling vortex of air, water mist, and fine calcium carbonate aggregate. Not grit blasting. Not pressure washing. TORC is a conservation cleaning system designed specifically for heavily soiled historic stone where steam alone will not shift the soiling.
TORC uses a vortex nozzle that produces a swirling cone of compressed air, water mist, and very fine aggregate. The aggregate is crushed calcium carbonate, typically between 40 and 120 microns in diameter. That is two to four times finer than standard grit blasting media. The vortex action means the aggregate arrives at the surface at a tangent rather than head-on. It shears off the soiling layer rather than blasting through it.
The practical result of this geometry is that TORC can follow carved detail, move around undercut surfaces, and clean into narrow reveals without rounding the arrises of mouldings. On a Portland stone facade with deep string courses, decorated cornices, and carved keystones, this distinction is significant. The stone surface is not abraded. Original tooling marks are preserved. The cleaning depth is controlled by nozzle distance, working pressure, and dwell time, all of which are calibrated during test cleans before any full application begins.
TORC is listed on Historic England's approved methods register and is accepted by conservation officers across London boroughs as a standard specification for heavily soiled limestone and Portland stone.
DOFF superheated steam is our first-choice method for most stone cleaning. It is non-abrasive, leaves no residue, and requires no chemical intervention. For recent soiling, biological growth, and light to moderate atmospheric deposits, DOFF is sufficient and TORC adds nothing.
TORC is specified when the soiling is an established sulphate crust. On sheltered Portland stone surfaces, sulphur dioxide in the atmosphere combines with the calcium carbonate of the stone to form calcium sulphate. The result is the black or dark grey crust characteristic of undersides of cornices, window reveals, and any face not regularly washed by rain. DOFF steam softens and removes this crust in many cases. On heavy or long-established deposits, steam alone does not generate sufficient mechanical action to detach the sulphate layer without dwell times that risk thermal stress to the stone.
In these cases, TORC provides the additional shear action that steam lacks. The two methods are frequently used together on the same building: DOFF on rain-washed faces and biological growth, TORC on sheltered elevations with heavy crust. Each face is assessed and specified independently.
TORC is not grit blasting. The aggregate is significantly finer, the working pressure lower, and the vortex delivery mechanism changes entirely how the particle contacts the surface. A correctly specified TORC clean leaves the stone texture unchanged. A grit-blasted surface is visibly abraded and the damage cannot be reversed.
TORC is also not appropriate for every stone. Soft sandstone, already-friable surfaces, and any masonry showing active decay are not suitable substrates. London stock brick is not appropriate. The method is designed for harder limestones and should be specified on that basis. Confirming the stone type and its current condition is part of the diagnostic process before any method is recommended.
No TORC application proceeds without test cleans. This is standard practice, not a formality. Test panels of approximately half a square metre are applied in two or three inconspicuous locations using different pressure settings. These are assessed after 48 hours and again at one week, because some surface responses are not immediately visible. The test panel assessment informs the full specification.
On listed buildings, the test panel results are documented and submitted to the conservation officer alongside the method statement before full works are authorised. We prepare all documentation and manage the submission process as part of the service.
TORC cleaning on a listed building requires listed building consent. The method statement submitted for approval covers the aggregate specification, nozzle type and configuration, working pressure range, test panel locations and results, and the assessment criteria for the finished clean. A poorly prepared submission causes delays. We manage this process with enough detail to avoid them.
In conservation areas, external works to unlisted buildings may also require prior approval from the local planning authority. Requirements vary by borough. We advise on the specific position for each building at the initial site visit.
Yes, when correctly specified. TORC is on Historic England's approved methods register and accepted by conservation officers across London as a standard approach for heavily soiled limestone and Portland stone. It requires listed building consent, and a full method statement must be submitted and approved before works begin. We prepare and submit all necessary documentation as part of the service.
The aggregate used in TORC is two to four times finer than standard grit blasting media, and the vortex delivery means it contacts the surface tangentially rather than head-on. Grit blasting abrades the stone surface. TORC shears off soiling without removing or rounding the underlying texture. They are not interchangeable. Grit blasting is not an accepted method on historic masonry.
Not on soft historic brick such as London stock. The aggregate action is too aggressive for a porous, low-fired brick. On harder engineering or blue brick in good condition, limited use may be appropriate, but our default for brick cleaning is DOFF steam. We assess each building individually before specifying any method.
A typical Victorian or Georgian stone facade will take two to four weeks depending on access, elevation complexity, and the depth of soiling. Additional time is built in for test panels, and on listed buildings, for conservation officer review before full works proceed. A programme is provided at the quotation stage.
Yes. The spent aggregate and removed soiling are collected at scaffold base level and disposed of as controlled waste. On urban sites, containment sheeting prevents aggregate reaching adjacent properties, pavements, or drainage. All waste management and disposal is included in the works programme.