Use of image analysis to evaluate surface dispersion and covering performance of nanolime coatings sprayed on heritage material substrates

Abstract

Coatings are often used to reinforce the surface of monuments, although little is known about their surface dispersion and effectiveness. This paper examines the surface distribution of Ca(OH)2 nanoparticle-based coatings (Ca(OH)2-NP). The coatings were sprayed on different substrates and studied by image analysis software and microscopy. Using image segmentation techniques the phase of interest (coating) was separated from the background material and evaluated. In control surfaces, up to 92.73% of the examined area was coated by the nanoparticles. In contrast, when the treatment was sprayed on building materials the NP-coatings were preferentially deposited in weaker zones, such as cracks or defects of the surface. In this case, the processed images revealed that less than 30% of the examined surface was coated by the NP-coating.