Water heated to well over boiling point and pressure sprayed on to masonry is an efficient way of removing grime and some applied finishes without damaging the stone. Suppliers of systems to deliver the superheated water have been finding better ways of doing it. NSS takes a look at some of them and an alternative method.

ONE OF THE results of using a superheated water cleaning system can be clouds of water vapour in cold weather. It is quickly dispersed if the system is being used on the outside of a building but it can be a deterrent to using the method on interiors. Now it no longer needs to be.

Restorative Techniques, based in Bristol, has developed a version of its ThermaTech with a recovery system that takes away the water vapour as well as the debris that is removed by the cleaning.

The new ThermaTech with the recovery system has already been used by William Anelay, the specialist stone and conservation company headquartered in Osbaldwick, Yorkshire, inside Wakefield Cathedral (it is pictured during the work below). It is part of Cathedral’s Project 2013 programme to clean and repair the building for its 125th anniversary as a Cathedral. Before becoming a Cathedral it was a church and most of the current buildings were constructed in the 15th century. Some of the dirt being removed by the 150ºC water seems to date from that time.

One 110V ThermaTech and one 110V recovery unit will run two working heads, effectively doubling the capacity of the system by having two operators using the same unit – you can see the hot water ‘splitter’ between the wheels of the ThermaTech in the picture. That’s the red hose, because Restorative Techniques like to provide a warning that hoses with 150ºC water going through them will be hot. The ‘Y’ connector between the recovery castor wheels combines the pipes coming from the head for the waste collection.

This is not a simple vacuum cleaner. At these kind of temperatures a special unit is needed, especially as it is enclosed to capture both the moisture and the waste. It includes a condenser and filters. Once the water is condensed it can be drained off so the operators are not frequently having to stop work to empty it.

William Anelay has since moved the recovery system ThermaTech it has bought over to Wentworth Castle for another cleaning project there.

Restorative Techniques is now in its fourth year of trading and its ThermaTech, along with the Vortex gentle abrasive cleaning system and other cleaning products in its range, are widely accepted and used by major contractors and are being specified for a number of important conservation projects.

STONEHEALTH has introduced a new version of its DOFF superheated water cleaning system. It is called the DOFF Integra. After lengthy and exhaustive site trials, Stonehealth believes the new developments on the DOFF Integra offer substantial benefits to the stone cleaning industry, although the company emphasises that it will continue to fully support the original DOFF, which is widely in use.

The Integra is available in either 110V or 240V versions and 50 or 60 cycles.

The DOFF Integra advantages include:

• An all-in-one unit carrying both pump and hoses.
• Two wheels to make it easy to manoeuvre on-site, while two additional wheels on the frame aid loading into vehicles.
• A jerry can fuel tank that can easily be changed when empty (a spare is supplied with the unit). The jerry can is carried in a bund within the frame of the DOFF Integra.
• Quick change, self-sealing hose connections for both the fuel and water hoses are supplied as standard to avoid leaks. The replacement jerry can fuel tank is easily exchanged with a unique fitting.
• Easy control by the operator. The desired temperature can be set and when it is reached an amber beacon will flash to show at a glance that the system is ready. It will also be immediately noticeable if the temperature drops for any reason. This will also be a warning to others that the machine could be hot to touch.
• A thermal dump valve on the pump to eradicate the possibility of thermal shock on the ceramic pistons if it is left running. This also enables the pump to remain near the source of power so that lightweight cables can be used from the pump to the hot box (especially helpful with the 110V machine on-site).
• A resettable fuel filter restriction indicator on the control panel.
• A resettable overload trip on the hotbox.
• Tamper protected ‘hours run’ recorder.
• Emergency ‘STOP’ button.
• Unique DNA Identifier theft deterrent. The pumps and hot boxes have the machine’s individual identifier recorded against the purchaser. The ID is also hidden at other points on the machine. The number is displayed on the integral dashboard. To remove it a thief would have to destroy the dash and render the machine useless or deface the dash, making it obvious the unit had been stolen. Apart from being a proven deterrent to criminals, this marking allows the Police to return suspect machines to Stonehealth so they can be repatriated to their rightful owners.
• Comprehensive, easy-to-use control panel.
• Easy access for straightforward and economical servicing.
• A user’s guide that stays with the machine in a protective tube within the frame.

DOFF has been widely accepted for stone cleaning since it was introduced by Stonehealth 18 years ago. It has been used to clean many famous historic buildings at places including Blenheim Palace and Chatsworth House, to name but two. It is also used by the Commonwealth War Graves Commission to keep the memorials to the armed forces clean and free from algae.

And while DOFF is straightforward to use, it can be abused to produce unwanted results of over or under cleaning, so to ensure that only bone-fide contractors who have had Stonehealth training are awarded work, Stonehealth has introduced a rosette symbol (pictured above) to identify contractors who have met the company’s standards of operation.

CLEANING sandstone has a chequered history and has been known to leave an all too chequered result on the cleaned building. But WGL Stone Clean, a cleaning and restoration company in Leeds, believes it has a solution using an acid washed off with superheated steam.

Bernie Coleman runs the company and says he has developed some useful improvements to standard cleaning techniques over the years, including dry-fog nozzles for dust suppression during abrasive grit blasting. In spite of the name they are not dry, but use a thin envelope of water to surround the grit as it leaves the nozzle.

His latest innovation, which he calls Steamacc and has been perfecting for nearly five years, is this use of acid with superheated steam, which he has used to clean the Hollington sandstone of the Church of St Francis of Assisi in West Bromwich. It was built in 1940 at least in part by Italian prisoners of war.

Bernie Coleman had used both proprietary acid products and superheated steam for cleaning and thought the two together would make an ideal way to clean masonry quickly and efficiently using lower concentrations of acid, which would be good for the environment as well as the building.

To give customers confidence in the method, in 2010 WGL commissioned the Department of Civil Engineering at Leeds University to investigate and report on the process. The report is available as a PDF that can be downloaded from WGL’s website (www.stoneclean.co.uk/university_report.pdf).

It concludes: “In summary, the cleaning process was found to preferentially affect the cementitious material between sand grains, whilst chemical attack of the sand grains themselves was minimal.”

Bryan Martin, architect to the Church of St Francis of Assisi, heard about the process and made contact with Bernie Coleman. He admits to being to a certain extent dubious as well as intrigued by what he describes as “this novel foray into acids as a method for cleaning stone”.

The wisdom of cleaning sandstone has been the subject of many published papers and articles and remains unresolved. Nevertheless, the Hollington stone of the church was black in certain areas and looked dirty.

Bryan Martin had already experimented with some cleaning methods but was disappointed with the variable results. He asked Bernie Coleman if he would be willing to send a team down to conduct a trial.

Satisfied with the test sample area and the detailed consultation given by WGL Stone Clean, the team was onsite several weeks later.

The original plan was to clean a part of the north elevation to coincide with a major re-roofing project. But Bryan was sufficiently pleased with the results on the north elevation to extend the cleaning to all elevations that were readily accessible without putting up more scaffolding.

Bryan Martin was delighted with the result, particularly on stylised figurative carvings of saints around the doorway that had been revived brilliantly by the Steamacc process.

It is not surprising that most of Thomann-Hanry’s UK façade cleaning projects are in London because the discreet system that uses a cherry picker – albeit a 40tonne cherry picker – to carry out the work with minimum disruption is ideal for the crowded city.

Thomann-Hanry does work outside London – it is currently tendering for a job in Leeds – but London, with its high density of limestone buildings to be cleaned, remains the company’s main market.

The work is carried out by an operator in a cabin on the end of the cherry-picker arm. The cabin has an apron that enables it to get close to the façade being cleaned and at the back of the cabin a fan that nearly fills the back wall draws the gently abrasive aluminium silicate used for the cleaning, which is about the consistency of talcum powder, back into the cabin to be collected.

The operator is fully enclosed in a protective suit and it is the skill of the operator that produces an even clean to the extent required.

Australia House, between Aldwych and The Strand in London (pictured right), is one of the latest buildings to have been given the ‘façade gommage’, as the French company calls its process.

The stone of the 5,000m² façade of Australia House took 20 days to clean using this process – that is about 200m² of stonework a day, which John Rolf, the company’s Business Development Director, says is about average. Windows do have to be masked while the stone around them is cleaned, but because the work progresses so quickly that usually only means they are covered for 20-30 minutes.

Another advantage of facade gommage is that it is a dry process. In fact, if the weather is too wet the work cannot proceed because the fine aluminium silicate powder sticks to the wet surface of the building. And once the building is cleaned, Thomann-Hanry will also carry out repairs, repointing and other work, such as regilding, from their cherry picker.

THE GRANITE Titanic Memorial in Liverpool has been cleaned and regilded by Ben Murphy of Monumental Conservation & Restoration. It was cleaned using the ThermaTech superheated water cleaning system from Restorative Techniques to mark the centenary of the ship’s one and only fateful voyage this year.

The memorial was created by the renowned sculptor Sir William Goscombe John.

Although the Titanic did not visit Liverpool on its maiden (and last) voyage, its owner, White Star, had its head office in the city and had only started sailing out of Southampton instead of Liverpool five years earlier. As many as 10% of the ship’s crew came from Merseyside, and most of the key officers and crew had originally sailed from Liverpool for White Star. Many of them still lived there in 1912.

The 14.6m high memorial sited near the iconic Royal Liver Building was unveiled in 1916 and, following its £8,500 facelift, was rededicated this year to mark the centenary of the Titanic disaster.

The memorial is officially called the ‘Memorial to the Engine Room Heroes’. It was paid for partly by the Institute of Marine Engineering, Science & Technology, the membership of which encompassed the 244 engine room crew who died when the Titanic hit an iceberg and sank.

But by the time the memorial had been built, RMS Lusitania and other ships had also been sunk in the first years of World War I, so although it has always been known locally as the Titanic Memorial there was nothing on it to indicate it commemorated the engine room casualties of that particular tragedy.

Until now. As well as being cleaned and regilded (with shrapnel damage from World War II having been left unrepaired as part of the memorial’s provenance) for the first time a presentation board has been put up telling the story associating the memorial with the Titanic.