The comparative analysis of biological growth and common cleaners based on organism identification and biological mechanisms

Biological growth on stone monuments and buildings is a common concern in architectural conservation. It is usually removed through the use of commercial biological growth cleaners. There are a number of these products on the market whose efficacy can vary by growth type and substrate. With years of experience a conservator may develop a sense of what products work best based on the type of biological growth present. However, most of this knowledge is based on trial-and-error in the field. This thesis takes a more systematic approach to cleaning biological growth. Popular commercial products owe their efficacy to the susceptibility of different biological organisms to the active ingredients present in the cleaner. Different types of organisms have different reactions and immunities to certain chemicals, or are affected to different degrees by the cleaners and application methods. Therefore, not all cleaners are equally effective on all types of biological growth. Past studies on the subject of biodeterioration have taken two approaches: looking at the DNA identification growth found on stone, and testing the responses of different forms of biological growth to commercially available biocides. These commercially available biocides are not the same as commercially available cleaners that work through biocidal mechanisms, with cleaners generally having lower toxicity and are subject to less strict government regulation. This thesis compares and analyzes the alterations caused by each chemical agent on specific forms of biological growth. This was accomplished through the collection and propagation of samples of biological growth and laboratory testing. Several forms of biological growth, including algae, lichen, and moss were first visually identified using state and local databases with information such as cellular structure, growth type, and geographic location. Algae samples were grown in petri dishes and tested along with larger samples of lichen and moss in the laboratory. The samples were monitored before, during, and after treatment. The effects of the cleaners were analyzed and compared to understand any differences between the reactions of cleaners and growths, and to what each growth was most and least vulnerable. The long-term potential for regrowth was also considered through the re-examination of sites cleaned for a prior thesis in 2011. Three sites cleaned with several of the cleaners included in this thesis were examined three years after cleaning to evaluate the long-term effects of the cleaners. The results from this thesis can assist in the design of custom biological growth treatment plans based on the taxonomic classification of biological growth and the substrate on which it grows.