Cleaning Methods

Cleaning Methods

Types of cleaning methods employed by WGL Stoneclean include:

Detergent/Water Cleaning

For lightly stained Portland Stone Facades water cleaning only Nebulous Technique is often sufficient. For other lightly soiled exteriors, a specialised form of detergent is sprayed onto the building at low pressure. The detergent is then washed from the surface using high-pressure jets of cold water. In certain circumstances we will use hot water at high pressure to complement the cleaning action of the detergent for rinsing. Detergent techniques are invariably used on artificial stone (artstone) facades. Our level of experience ensures that only the required amount of dirt is removed leaving the masonry fabric undamaged, yet perfectly clean. We also have a special detergent to clean stainless steel cladding.

For heavily soiled exteriors. Here the WGL Stoneclean surveyors and operatives will decide upon the correct type and concentration of acid to be used. Very often small trial areas will be cleaned to check the concentration required. This choice is dependant on the sort of masonry used on your property and the amount and depth of soiling. As WGL Stoneclean carry out their own acid dilution, concentrations are easily adapted to the degree of staining. In the last three years, WGL Stoneclean has pioneered the use of using a super-heated steam wash-off after acid spraying. With this technique acid dilutions are significantly reduced and dwell times can be reduced to seconds. Acid cleaning is not very aggressive when applied to brick or stone surfaces. The solution only attacks the top one or two grains of the surface allowing the water/steam jet to penetrate into the surface and remove the small carbon deposits. For the technically minded, if the average grain size of the stone is 2-500 microns and the stone thickness is 23cm, then over an average building life of 100 years, acid cleaning will reduce the building life by 2.6 months! Using this unique acid wash WGL Stoneclean will produce clean old buildings with the mineral salt colourings of the natural stone readily visible over many decades of air borne industrial pollution. WGL Stoneclean operatives will firstly protect glazing and other external features with heavy duty polythene film and masking tape or a brushable, peelable PVC film, which is both water and acid proof. This acid solution is applied by a low pressure sprayer onto the surface of your property ensuring that none is splashed onto surrounding features. After the solution has been left for a pre-determined time – the acid and the soiling are sprayed off with jets of super-heated steam at 150 degrees centigrade at a pressure of 150 to 170 bar. Because high volumes of water are used, the residual acid solution is extremely weak and therefore safe. We have successfully cleaned buildings immediately adjacent to water course with no water borne acid contamination.
We employ acid based cleaning techniques with mechanical scrapers when we carry out Mortar Stain removal on new buildings.

Other Chemical Cleaning
We also have experience in the use of Sodium Hydroxide cleaners for the removal of surface carbon staining that is sometimes encountered after fire damage or resulting from the use of old fashioned bituminous paints. We have experience of cleaning special types of brick notably yellow bricks found in buildings across the North. We also store and use other specialist chemical cleaners Aluminium Facades for example. We have experience of the use of peelable latex films that we employ to clean delicate internal stained stonework in situations where chemical or abrasive cleaning is not appropriate.
We have an extensive arsenal of chemicals and solvents that we use for graffiti removal in combination with our super-heated steam generator. We can also treat the cleaned masonry with chemicals after cleaning, minimising the shadowing caused by graffiti removal.

Sealing and Biocides
After an external elevation has been cleaned, we are now happy to recommend the use of modern silicone based water repellent sealers that will allow a building to breathe from the transmission of gases but that will prevent the ingress of water. We would also be happy to advise on the choice and application of biological growth inhibitors for external masonry.

Abrasive Blasting
For very heavily soiled exteriors. WGL Stoneclean surveyors will decide on the type and size of abrasive to use. Calcium Silitate based abrasives are usual, with no “free” silica, but other abrasives are sometimes employed. We normally use abrasives with a Moh hardness rating of betwen 6 and 7. Our surveyors will also select the pressure to be applied in the blast process to retain as much “character and colour” as possible on the cleaned surface. Where we find particularly soft substrates we will use either a pressure regulated blast process or look to use a softer abrasive such as walnut shell or calcium carbonate with Moh hardnesses between 3 and 5. Abrasive blasting is the most aggressive of our processes, but our extensive knowledge and experience ensures that your property will emerge clean whilst retaining its character. Before we commence work, we will of course protect all windows and external features. We normally employ a wet blast process for external walls to minimise the dust generated by the blast process. The air/abrasive stream emerges from the nozzle at just under 500 miles per hour. Although we protect central heating boiler vents, we do managed to blow out pilot lights! After cleaning, we pay particular attention to cleaning up the abrasive waste on your property and, if necessary, on any adjoining properties.

Super-Heated Steam
We have using a super-heated steam generator called DOFF for several years. DOFF produces steam at over 150 degrees centigrade as its cleaning medium. The DOFF process is particularly suited to the removal of oil based paints from softer surfaces, such as brick, without damaging the underlying surface. We have also used it to remove high lead bearing paint from cast iron surfaces without generating a dust hazard from the removal process. DOFF kills biological growths on building elevations on contact and will also sterilise floors walls and ceilings after flooding.

Stone/Brick Restoration and Re-pointing

After cleaning operations have been completed we are regularly asked to extend our works and repoint, repair or replace damaged masonry.
We have a great deal of experience in working with a wide range of mortars, from simple cement mixtures to the use of Hydraulic Lime mortars, now widely specified on Heritage Sites. Joints are always racked out to a depth twice the joint width and the joints then brushed and wetted before filling. Our operatives have particular skills in colour matching new mortar to the existing mortar colour. Latterly we have become acquainted and skilled in the use of the newer vibratory and orbital tools for the accurate raking out of narrow joints. These tools are particularly useful when heritage tile facades require attention.

We have experience and knowledge of a wide range of brick and stone repair mortars that, when used with appropriate types of Stainless Steel re-enforcement, can provide a repair that will last almost as long as a natural stone replacement. Should a replacement be required we have contacts with quarries across Yorkshire and can source re-cycled or new hand made bricks.