Quality index control for building products made of natural facing stone

Purpose is to assess the influence of technological and natural factors on the decorative properties of natural facing stone to identify the regularities of changes in lightness and saturation of its surface. Methods. To assess the effect of technological and natural factors on the decorative properties of natural facing stone, methods of digital processing of images and infrared spectroscopy have been applied. The methods make it possible to obtain the data on the influence of mineralogical and chemical composition on the decorative properties of natural stone and characterize the physicochemical processes that occur during the natural stone processing by different methods. Findings. The regularities of changes in surface gloss of facing stone after its chemical treatment have been specified. It has been proved that all chemical impregnations increases stone gloss; the lower the initial indices of the natural stone surface gloss are, the greater stone changes are observed. In turn, that is caused by the fact that each type of natural stone has its own gloss limit. The regularities of lightness changes and surface saturation of natural facing stone after chemical treatment have been defined. They indicate that all agents reduce lightness and increase saturation of the natural stone surface (except Impregnation agent 3). According to the identified regularities, it is possible to control quality indices of the natural stone surface with simultaneous provision of uniform colour shade of a stone-faced building. The main problem arising during the study of surfaces of natural stone samples by means of infrared spectroscopy was inhomogeneity of its mineral-chemical composition over the sample area. As a result, various spectra have been obtained that are difficult to identify without the prepared reference samples. Complete infrared spectra of the natural stone surfaces of Pokostivskyi granodiorite and Bukivskyi gabbro. Both Pokostivskyi granodiorite and Bukivskyi gabbro have different infrared spectra within the analyzed range of wavelengths that can be explained by the difference in mineralogical composition of both natural stone types. Originality is in identifying the regularities of changes in lightness and saturation of the natural facing stone surface after its chemical treatment. Practical implications. The determined regularities of changes in lightness and saturation of the natural facing stone surface can help control the quality indices of the natural stone surface with the simultaneous provision of uniform colour shade of a stone-faced building.