How Do You Clean Stone Work Of Cathedrals?

20 Apr Rock Cleaning

Posted at 13:06h in ARTICLES

Spencer Hall ACR

Stone cleaning is an important aspect of works in the conservation world. Cleaning doesn't simply help to improve overall advent, just more importantly can assistance remove potentially harmful atmospheric pollutants which can harm stonework irreversibly. Cleaning can also aid to expose further potential harm and place masonry requiring repair or replacement. Biological growth tin can actually harbour moisture and in plow lead to accelerated decay and so regular maintenance can exist of import.

Consideration should still always exist given to the level of clean that is to be achieved. Information technology is important that we exercise not over clean and strip stone of all its chronology, and so a judicious approach should always be undertaken. This can be difficult to define sometimes, every bit the 'correct' level tin can be somewhat subjective. As e'er, skilful communication is the fundamental to understanding customer expectation, the context of the work and what is best for the object (whether building, sculpture or monument).

Wherever possible, an approach of minimal intervention volition be strictly adhered to when working with celebrated fabric.

• Wherever possible, like for like repairs will e'er exist carried out and whatsoever "strange" materials introduced, kept to an absolute minimum.
• New repairs should non disturb the aesthetics of the architecture, simply under scrutiny from a specialist be notable.
• All replacements/repairs should only exist carried out with the help of documentary bear witness; no speculative works should be undertaken.
• It is imperative that only craftspeople who are experienced with traditional materials should ever undertake a repair in a building of historical significance.
• All piece of work should exist extensively documented in both photographic and annotated forms; before, during and after whatever intervention.

Before cleaning is undertaken, a biocide may be practical to help remove the growth. Moss, algae and lichens attach themselves to stonework, tin can encourage a damp environs and exacerbate potential breakup.

Following cleaning, a bio-inhibitor can also be practical over again to help discourage the regrowth of similar.

Doff

Doff/Torick/Hot Box/Thermatech – The Doff is the most commonly used brand name for building conservation specific superheated pressure washers. It is Non a pressure washer as i might use on say a patio etc. The advantages of the Doff as a piece of technical machinery is that both pressure level and temperature are fully controllable – allowing the use of cold water at minimal force per unit area to be used all the fashion up to a constant steam temperature of 150 degrees at pressures of up to ninety bar. The flexibility of this found allows (following trials) for targeted areas to be cleaned in close detail. Care should be taken using the Doff, due to the fact it is operated by paw and so a systematic approach should be taken – cleaning from say top left-mitt side, across to the bottom right hand side in smooth sweeping movements.

Joss

Jos/Torc are all variants of the same machine and work very differently to the Doff (described in a higher place). The Jos has been a cleaning tool for over 20 years and was adult by German engineers. The Torc is an English alternative, but works in the aforementioned manner. They all operate on the principle of h2o under pressure being practical through a nozzle to the face of masonry in a vortex. This swirling vortex sweeps across the surface and very gently washes/abrades the surface. A range of aggregates can be added to this vortex to increase the effectiveness of the clean. These aggregates are rated on the Mohs scale (which measures hardness) – a 'hard' material being something like corundum pulverisation (nine Mohs) through to a 'soft' textile like talcum pulverisation (1 Mohs). The Mohs calibration is a purely ordinal scale and as such, corundum (ix) is twice as hard every bit topaz (eight), but diamond (10) is four times as hard every bit corundum. The 'normal' material however is Calcite pulverisation which is rated three on the Mohs calibration. As with all methods here, care must be taken non to overclean and remove the confront of the masonry and this is very much downward to the condition of the substrate, the choice of amass used and nearly importantly, the skill of the operator.

Nebulus cleaning

Nebulus water cleaning is mayhap the most natural and subtle method of cleaning, as the process replicates rainwater running over the surface of the building which gradually washes abroad surface dirt. The method by which this is completed relies on a prepare of nozzles beingness prepare across a proportion of the façade (working from top downwardly) leaving them to run continuously for a menstruum (which can be anything from ten minutes to several days, depending on level of soiling) and then repeating the same process over again on the next area. Whilst this will give a expert overall basic clean it does not target problem areas and so it often used in conjunction with one of the other methods listed.

Micro air-abrasion

Not unlike the Jos (described above), micro air-chafe systems work past forcing air through a compression bedchamber into which abrasive particles are placed. The air carries said aggregates downwardly the hose and out via a nozzle onto the area in question. Type of aggregate, pressure and the quantity of annoying used are the 3 main factors which control the effectiveness of this equipment. Unlike the Jos, no water is utilised. I have used this to greatest effect on small delicate carved sculpture in a studio surround, although I practise empathise larger scale equipment is available on the market place for building facades. In the wrong easily, this could be as damaging every bit sandblasting and so merely a practitioner who understands the fundamentals of its use should be tasked with its deployment. Its employ is peradventure most appropriate in a conservation studio, although I have also used it in the field.

Chemical cleaning

Cleaning with chemicals is a wide field that can incorporate everything from mild detergents through to potent acids and alkalis. Acid and brine cleaning has fallen out of favour in contempo years and for good reason. High strength acids will react adversely with Calcium Carbonate (CaCO3 – limestone) and as well have the potential to damage both brickwork and some sandstones. Strong alkaline solutions can conversely be linked to the formation of salts on both stone and brick. In our opinion, the use of either on natural rock is probably all-time avoided. The cleaning of granite, brickwork and terracotta may sometimes exist advisable, only not bad care and consideration will need to be imposed and a suitable number of trials completed to constitute the best approach. As with all aspects of cleaning, low strength percentages should be employed first and increased merely if accounted absolutely necessary. Ammonium carbonate is mild element of group i cleaner and is frequently used held in a clay medium (the process of which is described in greater detail below) to soften black encrusted clinker. It works past reacting with Calcium Sulphate (CaSO4) on the blackened surface and forms both Calcium Carbonate and soluble Ammonium Sulphate (NH4)2SO4 which can exist rinsed abroad hands with the addition of water (H20) and light scrubbing.

Poultice Cleaning

Both 'clean' h2o and chemic poultices can be used to good outcome in cleaning and lifting staining. Poultices piece of work by cartoon out the stain using capillary action. The nigh mutual poultice medium used is Sepiolite (a clay pulverisation), although paper pulp is often added at 50:50 to produce a highly absorbent and malleable mixture that doesn't dry out too quickly. Sepiolite is a relatively inert Magnesium Silicate (Mg4Si6O15(OH)2·6H2O) and is frequently favoured as a medium in poulticing past conservators on stone sculpture. Another blazon of poultice pop in conservation cleaning to stonework is EDTA (Ethylene Diamine Tetra-acerb Acrid). The common form of this poultice is where the production is bound in a naturally produced latex (normally containing small amounts of ammonia). The ammonia acts as a useful cleaning agent in its own right and triggers the curing of the safety in one case exposed to air. This cured latex film tin can hands be removed mechanically, without the use of h2o and as both surface based dust and imbued dirt lifts with it, the removal results in a cleaned surface. This method was used to great issue to the interior of St Pauls during the major restoration completed a few years ago.

Laser cleaning

The give-and-take Fifty.A.S.E.R. is an acronym for Low-cal Distension by Stimulated Emission of Radiation. Laser can be used to clean carbonation/sulphation from a variety of substrates (limestone, sandstone, marble, terracotta etc) in a very controlled style. It is most suited to working on delicate material in a workshop environs, simply can be used successfully on site. At that place are however limitations, due to scale of operation and in turn toll. Trials should e'er exist encouraged to establish suitability and are influenced by nature of substrate, the level of soiling and other environmental factors. Hand held units now make it far more portable. All units withal run off a 240V supply (110V version is not currently available, but special dispensation can usually be gained for employ as a 'specialist' slice of equipment – an RCD breaker must of course exist employed) Rubber bug are paramount. Laser tin can damage retinas from a considerable distance away, so light shielding around the scaffold is essential. All adjacent areas MUST also exist well signed to avert people unexpectedly chancing across it in use. Goggles must exist worn and these are specific to the wave length of laser being used and and then guidance must be sought. The control offered by laser cleaning enables the conservator to remove unwanted layers without over-cleaning the valuable surface of the artwork; patina, fine surface detail, tool markings and important surface coatings can exist preserved. Laser cleaning systems provide the conservator with an extremely gentle method of cleaning which can be used to remove dirt from very fragile surfaces. Click here to see the instance study on St Georges Cathedral, Southwark

Stone Cleaning

Further to stone cleaning it is often necessary to reassess status. If losses to joint material have occurred or friable cloth is removed, then these areas should be reassessed before reinstatement is considered.

To recap, when considering cleaning it is important to try and achieve a consistent finish that meets expectation just does not strip the object fully of its integrity. A rest should ideally be sought between removal of dirt and detritus and retention of some of the accumulated patina which is in keeping with the age of a piece. Over-cleaning can be viewed as 'harm' by many in the conservation earth and and then trials should exist completed in accelerate to an area where they can be evaluated without having impact on the overall finish.

For further assist or information on any aspect of the services or advice that PAYE Conservation can provide please in the first instance call Spencer Hall on 020 8857 9111

Source: https://www.paye.net/stone-cleaning/

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