Thermographic imaging for early detection of biocolonization on buildings

Biofilms developed on historical heritage buildings are made of various microbial communities settled and anchored in a substrate. They provide a good medium to the development of macroscopic vegetation which causes irreversible and physical damage to stone structure. Infrared thermography (IRT) measurements have been performed in laboratory scale to investigate the applicability of this non-destructive technique to an early detection of microbial biofilms on stone surface. Detecting biofilms before stone soiling is important in Cultural Heritage conservation to avoid both irreversible damage and building restoration costs. Active IRT was set up on a French limestone used in many French buildings and monuments. Samples were collected after six-months of exposure in an outdoor biofouling test during which they were colonized by microbial biofilms. They have been compared with controls with no biofilm. Experimental set-up has been carried out in dry and damp conditions to simulate different climatic conditions. First results displayed a different thermal response: stone surfaces with biofilm reached higher temperatures and they cooled down faster than row stones. Biofilm entailed a change of the stone thermal behaviour similar to a monolayer. IRT detected biofilm with a better efficiency in dry than in damp condition.