Effect of Mineral Pigment Processing on the Colorimetric Response and Weathering Deterioration of Coatings for Heritage Architecture

The effect of mineral pigment processing by sedimentation (MS) and ball milling (MG) on the colorimetric response and surface deterioration under weathering of coatings formulated with polyvinyl acetate (PVAc) at 20%, 40% and 60% was comparatively evaluated; 78 coating formulations with valid records were evaluated, with five replicate specimens prepared for each formulation, resulting in 39 paired MS-MG comparisons for colorimetric analysis. The pigments were characterized by particle-size analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS), while the coatings were evaluated using the NCS system and natural weathering exposure. The colorimetric comparison showed predominant stability between MS and MG, with 23 comparisons retaining blackness, 23 chromaticness and 22 hue. The differences depended on the pigment and PVAc concentration. During exposure, MG presented lower maximum levels of cracking, detachment and blistering than MS; however, discoloration showed a differentiated response, with higher values in MG-20% and MG-40%. The results indicate that pigment processing influences coating performance, but its effect is not uniform across all evaluated properties. MG showed a more favorable surface response under the experimental conditions studied, without demonstrating overall superiority in chromatic stability.