Control of Microbial Growths using Biocides

Biocides in use. There are 5 main types of biocides that are active against microbial growths  

The desired biological action of biocides against unwanted growths on stone, of course, also means that these chemicals pose a threat to the natural environment if they cannot be restricted to the stone substratum. Thus the chemical and physical behaviour, especially their solubility in water and capacity to react with stone components, has an important effect on whether there is a risk of environmental pollution. The interactions with the stone, or indeed previous chemical treatments, could also lead to colour changes or even mechanical damage through crystallisation. 

Removal of weathering products may enhance the aesthetics of a building, but removal may be detrimental to cohesion of the structure of that part of the building. Statues, for example, may have sulfate crusts removed, but the crusts may be the only solid component of that part of the statue. Calcium carbonate may have long ago been replaced by calcium sulfate and so the details of a statue s face could be composed solely of weathering products. 

Biocalcification. An alternative to chemical consolidation of stone is the exploitation of a common phenomenon found in living organisms known as biomineralisation, which produces shells in animals. Microorganisms can also be isolated from the environment or stone surfaces that are able to precipitate 

CaC03 in the form of calcite. Although biomineralisation has been observed for many years, the potential for its use in stone consolidation has only been explored relatively recently. Biocalcifying bacteria have been used to successfully promote carbonatogenesis on the surface of limestone buildings, statuary and monuments. This newly-formed carbonate is often resistant to mechanical stress, possibly due to the incorporation into crystals of organic molecules, produced as a result of bacterial metabolism. 

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