Bio-based coatings are a rapidly expanding market driven by consumer awareness and green regulations, but there are still some obstacles to be solved such as the high price of the final product, and the performance, that in many cases is inferior to the conventional ones. It is estimated that the bio-based coatings market increases at a compound annual growth rate of 9.5% and tends to reach 16.6 billion euros in 2027 and 17.9 billion euros in 2032. This study is focused on the design and development of waterborne masonry coating, with minimized content of volatile organic compounds contributing to a healthier indoor air quality, and with technical characteristics compliant to sustainable “green” building programs criteria such as LEED, WELL Building or BREEAM. The intended use of such a coating is internal walls and plasterboards, on overcrowded rooms as offices, malls but also on kindergartens, schools and domestic applications such as on childrens’ rooms and kitchens. Six coatings with different pigment volume concentration were formulated. Specifically, two versions of approx. 64% and four of approx. 44%, were prepared and characterized with various methods. The novelty, on the formulation of such coatings is based on the use of alkyd emulsion binder enhanced with colloidal nano-SiO2 and ingredients such as sustainable alginate rheology modifiers, and fillers derived of processed oyster shell powder. Important factors that have impact on bio-content and important manufacturing parameters were evaluated and specific properties such as whiteness, yellowness, contrast ratio and mechanical properties such as film hardness, adhesion, bending, wet scrub, stain and burnish resistance were scrutinized. Important results on microbial contamination, wet scrub resistance and yellowness depending on the pigment volume concentration and fillers composition, arise.