Inverness Castle: the red sandstone towers and entrance front cleaned with the DOFF steam system, seen from above with the scaffold coming down

Stone cleaning:

Stone Cleaning

DOFF and TORC cleaning, approved by Stonehealth

Our role
Stone cleaning by our own trained operatives, within our masonry contracts or as a specialist package for a main contractor
Systems
Stonehealth DOFF superheated water and steam; Stonehealth JOS/TORC low-pressure swirling vortex of water, air and fine inert granulate; hot and cold water washing; hand cleaning and poulticing
Removes
Carbon and particulate soiling, algae, moss and lichen, bird fouling, masonry paint and old coatings, cement laitance, efflorescence and limescale, graffiti, wax, oil and bitumen
Stone
Granite, sandstone, limestone, brick, terracotta and harled or limewashed walls; also bronze, copper and ironwork
Standards
BS 8221-1 code of practice for cleaning natural stone, brick, terracotta and concrete; trial panels approved before work starts; listed building consent where cleaning needs it
Projects
Inverness Castle, Greyfriars Church Aberdeen, Corrour Estate, Cowane's Hospital Stirling, Marischal College, Arbroath Courthouse, 30 The Square Huntly, Finnich Malise House

We are approved by Stonehealth Rosette for the DOFF and JOS/TORC stone cleaning systems: gentle yet effective methods that clean stone without damage, preserving its historic character. Cleaning is the one job on a building where the wrong tool, or the right tool in the wrong hands, does harm that cannot be undone, so we do it ourselves. Our operatives are trained on the DOFF and TORC systems, they work within LTM's own masonry teams, and they clean to an approved trial panel, not to a hose. The result is stone that looks like stone again: soiling, growth, paint and cement gone, the surface, the arrises and the tooling marks intact, and the wall left dry and breathing.

Corrour Estate: a granite gable half way through paint removal, the stripped stone on the left and the painted wall on the right
Corrour Estate as found: estate cottages that had been repointed in cement and painted, trapping water in the granite walls
Masonry paint lifting from the granite: the coating had to come off before the cement pointing could be raked out and the walls repointed in lime
The cleaning plant in the courtyard at Corrour: the compressor and pressure pots that feed the TORC nozzle, in one of the most remote villages in Scotland
A gable stripped of paint, with the last of the coating still sitting in the cement joints before they are raked out
The same estate buildings cleaned, cement and paint removed, and repointed in a hot-mixed lime mortar

Two systems, one approved standard

DOFF and TORC do different jobs, and knowing which to use, and when to use neither, is the skill. DOFF delivers a low volume of superheated water and steam, up to 150 degrees, through a nozzle at three to five litres a minute: enough heat to kill algae, moss and lichen at the root, lift bird fouling, chewing gum, wax, oil and most paint coatings, and sterilise the surface, without damaging pressure, thermal shock or deep saturation, so the wall dries within minutes. TORC is not a blasting system. Its nozzle creates a gentle swirling vortex of low volumes of water, air and a fine inert granulate, with apertures from 5 to 13 millimetres, and in trained hands it takes off carbon sulphation, lime and cement paints, plaster and cement residues, limescale and efflorescence from ashlar or fine carved detail while leaving the patina where that is wanted. Both are Stonehealth systems, and our approval under the Stonehealth Rosette scheme means our operatives have been trained and assessed in using them properly.

Trial panels first, then the whole wall

No elevation is cleaned until a trial panel has been agreed. Cleaning in Scotland can need listed building consent or planning permission in its own right, and the specification, usually to BS 8221-1, will set the standard the panel has to reach. We clean the sample areas with the methods proposed, let them dry, and reassess them with the architect or stone consultant before the sample becomes the datum for the whole contract. At Greyfriars Church in Aberdeen twelve sample areas were cut out across tracery, ashlar and entrance for the masonry consultant to approve before the Kemnay granite was steam cleaned and then taken down with a low-pressure wet slurry to match the adjoining Marischal College facades. At Clackmannan Town Hall the red sandstone was cleaned with DOFF against an agreed trial panel and the method adjusted surface by surface; at Fairburn Tower sample areas and trial cleaning were agreed with the architect before each process began. The panel also protects the client: what was approved is what the building gets.

A Victorian sandstone villa in Stirlingshire for a private client: the ashlar dressings and rubble walling cleaned with TORC and DOFF
Inverness Castle before cleaning: the south tower's north elevation with decades of cement render and repairs coming off the red sandstone
Inverness Castle: the north tower cleaned with the DOFF steam system and repointed in lime, the ashlar tooling and the corbelled parapet crisp again
Cowane's Hospital, Stirling, as found: the seventeenth-century almshouse painted and cement pointed, with moisture trapped behind the coatings
Cowane's Hospital after the works: the paint removed with the TORC system, the walls lime harled and limewashed and the stone dressings clean
Arbroath Courthouse after cleaning: the sandstone front descaled and DOFF cleaned, the lime repairs and new stone blended in

Paint and cement off, lime back on

The most common reason we are asked to clean a historic building is that someone painted it. Masonry paint and cement pointing seal a wall that was built to breathe, and the damage shows as damp inside and spalling outside. At Corrour Estate, a remote Highland village of granite estate buildings reached by rail or a long track, five buildings had been cement pointed and painted; the paint was taken off the granite, the cement raked out, the wallheads and chimneys rebuilt and every joint repointed in a hot-mixed lime mortar, all under a NatureScot bat licence. At Cowane's Hospital in Stirling paint removal was trialled with DOFF, then carried out with TORC, which proved more effective on the coatings found, before the walls were lime harled and limewashed. At Finnich Malise House the sandstone was DOFF cleaned and the failed masonry coatings taken off with TORC before new Cove red sandstone indents went in, and at Cromwell Tower in Old Aberdeen TORC took the thin cement laitance off the brick face to give the new lime harl a clean, absorbent substrate. At 30 The Square in Huntly paint and grime came off the granite and sandstone frontage with DOFF before the corner turret was rebuilt.

Cleaning as the first repair

Cleaning is also diagnosis. Until soiling, growth and old coatings are off, nobody can see what the stone is really like, which is why on our masonry contracts the DOFF goes on before the survey is finalised. At Inverness Castle, a Category A listed building being restored for The Highland Council, vegetation was removed by hand and the sandstone cleaned with DOFF before the cement repairs were taken out, the stone defrassed and the decayed blocks replaced. At 1a Pumpgate Street in Inverness and at St John the Evangelist Church in Portobello, selective DOFF cleaning exposed the flaws in the stone and set the repair schedule; at Arbroath Courthouse the sandstone was descaled and cleaned with DOFF so that most of it could be kept through consolidation and colour-matched lime repairs rather than replaced. Where there is no masonry package, DOFF and TORC cleaning is a specialist package in its own right, as it was for Hadden Construction at Clackmannan Town Hall, with wash water collected and controlled on a narrow one-way street.

Greyfriars Church, Aberdeen: the Kemnay granite tower, belfry tracery and pinnacles cleaned, with the scaffold being struck downwards
30 The Square, Huntly: the granite and sandstone frontage DOFF cleaned and the corner turret rebuilt
Marischal College, Aberdeen: the Kemnay granite facades cleaned and repointed as part of our masonry package for Sir Robert McAlpine, decades of pollution gone from one of the largest granite buildings in the world
Finnich Malise House: the red sandstone bays and dressings DOFF cleaned and the old coatings removed with TORC, the harled walls limewashed

Granite, sandstone and brick

Each stone soils and cleans differently. Kemnay granite has a rough surface that holds dark particulate soiling and black gypsum crusts; it is hard enough to take a low-pressure wet slurry, and the Greyfriars Church specification called for steam to lift the organic growth and loose soiling first, then a wet slurry through a small straight nozzle to all granite surfaces, with run-off collected at three levels of the tower and bagged for disposal. Soft red and blonde sandstone will not take an abrasive at all, so it gets DOFF, hand scraping of crusts and biocide, as at Inverness Castle, Rose Street Foundry in Inverness and the sandstone villas and civic buildings we work on across central Scotland. Brick and terracotta take TORC for cement and paint residues. On bridges, such as Elgin's Bridge at Huntly, DOFF and hand work remove moss, efflorescence and calthemite before repointing. And at 1a Pumpgate Street, Silk House in Falkirk, Balgray House and Clebrig Lodge the cleaning sat inside a wider lime repair contract, which is where it usually belongs.

Containment, protection and record

Cleaning a building in a city centre is as much about what does not happen as what does. Windows, doors and rainwater goods are protected, scaffolds are sheeted and boarded lifts tanked so that slurry and water are redirected and collected rather than running down the facade or on to the pavement, gutters are kept clear, and residues are bagged and disposed of through the local authority's agreed route. Passers-by and neighbouring buildings are kept clear of every part of the process. Water flow and, on TORC, the granulate ratio, nozzle size and working distance are recorded against each elevation so that the standard set by the trial panel is held from the top of the building to the bottom. Where the specification asks for it, a biocide wash follows the clean, and a breathable water repellent impregnation can be applied once the walls have dried out and any repairs have cured.

What it means for your building

Clean, not scoured

Soiling, growth, paint and cement come off; the face of the stone, its arrises and its tooling stay. Nothing abrasive goes near soft stone or carved detail.

Our own operatives, Stonehealth approved

DOFF and TORC cleaning by LTM's own trained teams under the Stonehealth Rosette scheme, working within the same contract as our masons, harlers and conservators.

Agreed before it starts

Trial panels approved with your architect or stone consultant to BS 8221-1, consent in place where cleaning needs it, and the approved panel held as the standard for the whole building.

Over 25 years of heritage work

A multi-award-winning team with its own SQA-approved traditional skills academy, cleaning and repairing stone from castles and cathedrals to estate cottages.

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Stone that has lost its colour?

Send us photographs of the elevation and tell us what is on it, soiling, growth, paint or cement, and we will tell you which system will take it off safely, whether consent is needed and what a trial panel will show.

Discuss your project Call 01330 833 941

Cleaning on site

Stone cleaning case studies

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Preserving stone heritage, with our own in-house conservators