Chemical cleaning

Chemical cleaning :We offer a specialist cleaning service using various methods from conventional sand & grit blasting methods to special abrasive water jetting without harmful chemicals
To compliment the cleaning of a building we normally coat and protect the cleaned masonry with our 'Clearshield' Products

  

Until relatively recently, cleaning methods generally lacked proper specification and site control. This has resulted in a wide variety of techniques being offered by contractors without due regard to the full consequences of their effect, and usually little or no detailed consideration was shown by manufacturers or suppliers to this need. In attempting to deal with all types of dirt and surface coatings in one treatment, contractors and specifiers catered for worst-case scenarios, and over-treatment was the established norm.

In particular, insufficient consideration was given to the wide range of natural materials being dealt with and their relative susceptibility to deteriorate as a result. No building is homogeneous in its construction or detail. Materials such as sandstone, limestone, granite, brick and terracotta are liable to be bound by lime mortar. Some may be used in combination, and other factors such as variations in colour, texture, tooling and form are likely to be met. In many, the composition will vary, and different combinations can lead to the interaction of materials, one with the other. Decay may also be present and different patch repairs, with different substances at different times, may further complicate the issue.

A basic difficulty is deciding where to stop. This can lead to a form of facadism, with only the principal elevation being treated. However this approach has one advantageous side-effect: any change that subsequently reveals itself can be compared against the untreated return faces of the same stones at the extremity of the cleaned area.

The type of soiling also needs to be taken into account. In the cleaning debate, soiling is often pre-supposed only to be an external agent, with particulate deposition and reaction resulting from either wet or dry conditions. Damaging crust-formation can be evident on the surface limestone, but the prospect of benign mineral movement occurring from within the body of sandstone is rarely considered.

Biological surface soiling is equally complex, with bacteria, algae, fungi and lichens each seeking out the appropriate colonisation conditions within which they will flourish. Influencing factors in their growth can include atmospheric and micro-climatic conditions, fluid movement and concentrations, surface roughness and physical changes.

Once the building has been cleaned, incidents of resoiling, iron mobilisation, efflorescence, vandalism and graffiti further complicate matters.

Two fundamental methods of cleaning buildings have habitually been adopted, although a number of specialised techniques have become available in recent years:

Physical methods: these include brushing and rubbing, washing and steaming, wet and dry abrasives, or surface redressing.

Chemical methods: applied as liquids or poultices, these may employ the use of alkaline treatments, acidic treatments or organic solvents, singly or in combination.

Special techniques may promote the use of impregnated sponge, laser technology, ultrasonic equipment, heat lances, gypsum inversion, bacteria, poultices or gels, and surfactants (degreasants or soaps).

Not all treatments are appropriate for all materials, and extreme care needs to be exercised when deciding which system to adopt. Due to the need to minimise the risk of damage, the 'do not clean option' should also be borne in mind.
Measures to be adopted to minimise risk where cleaning is acceptable in principle

Determining the actual testing methodology, and the validity of trial area results, can be an elaborate process if it is to be carried out effectively and meaningfully. Topics that should be considered include colour measurements, depth profiling, surface roughness tests, and the use of scanning electron microscopy, determining the petrology (the geological structure of the stone) and pH values, porosity and permeability measurements, before and after test cleaning. Care needs to be exercised when contemplating the consequences of washing chemicals into underlying masonry during rinse-off stages, and the question of how to stop 'wash-in' occurring on porous stone surfaces when 'washing off' chemicals should also be addressed.