Sagging failures occurring immediately after spraying in a preerection ship block are uncommon when solvent-borne alkyd coatings have been used, but there are not conditions that induce the sagging failures, such as high coating thickness and humidity. These failures cause additional workload and cost because surface pretreatment and spraying have to be performed after removing the coating area in which the failures occurred. The authors performed rheology analysis for three types of the waterborne coatings to investigate the main factors that affect the sagging failures. Physical properties, such as drying time and sagging point at the various weather conditions, were studied to determine the effect of humidity and air flow condition to the sagging failures. The yield point, which affects the sagging point of the waterborne coatings, was analyzed using the hysteresis ramp method in order to estimate the sagging resistance of the wet film that was applied to the substrate vertically by airless spraying.

Subject
Films, Humidity, Water, Coatings, Yield stress, Viscosity, Spray coating, Shear, Fluid flow, Coating defects, Airless spraying, Sagging, Yield strength
Keywords:
shipbuilding, waterborne coatings, sagging, rheology, viscosity, thixotropy, hysteresis
Government work published by the Association for Materials Protection and Performance (AMPP) with permission of the author(s). Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2013
GOV
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