Effects of staining agents on an ornamental granite

Abstract

Abstract Natural stone is quite popular and is commonly used in building interiors, for its aesthetic appeal and for its performance, durability and environmentally-friendly composition. Natural stone also adds considerably to the real estate market value of houses. Different types of natural stone, including granite, can be used in interior design. The stones are thus exposed to staining and are affected differently depending on the staining agent involved. The European standard UNE-EN 16301:2014 defines a procedure for determining the sensitivity of ornamental stones to accidental staining. However, a more detailed study of the physical and chemical effects of such staining agents on stones is required. Adapting this standard, nine different stains (red wine, olive oil, instant coffee, ketchup, cola, citric acid , artificial urine, lime juice and blueberry juice) were applied to a granite commonly used in the Iberian Peninsula. The granite had a polished finish, and three cycles of staining-cleaning (with an anionic detergent) were applied. In the standard evaluation, a qualitative score is awarded on a text-based scale, by external evaluators . In this study, a more complex physical, chemical and texture evaluation of the granite surfaces was carried out to determine the sensitivity of the granite to accidental staining. Colour, roughness, hydrophobicity, gloss and texture were considered key parameters for evaluating the sensitivity of the granite to accidental staining. The sensitivity of the granite to staining clearly depended on the characteristics of the staining agents. In terms of aesthetic properties, all stains except lime juice caused significant colour changes on the granite surface. None of the stains, except red wine, caused important changes in surface gloss. The staining agents, particularly ketchup, blueberry juice and citric acid increased the wettability of the granite surface, thus further enhancing the absorption of aqueous solutions. Olive oil residues were not completely removed from stone surfaces after the cleaning process and therefore caused an increase in the static contact angle, although the stained granite surfaces remained hydrophilic . Citric acid solution caused a chemical interaction with quartz grains, highlighted by the formation of etch pits.