Limestone powder is a crucial ingredient in paint formulations, which enhances whiteness and serves as a filler, and it often comprises up to 60% by mass. One possible replacement for limestone powder is clam shell powder, which is rich in calcium carbonate. This study explores the use of clam shell powder as an alternative in water-based paints. As part of the study, clam shell powder was incorporated at 1–4% by mass, with comparisons to traditional limestone formulations. The findings indicate that paint samples containing 1–2% clam shell powder meet the standards outlined in TCVN 8652:2020 for wall emulsion paints. As the concentration of clam shell powder increased, a decline in density, hiding power, and fineness was observed, while adhesion, viscosity, and pH levels rose. Notably, all samples exhibited acceptable levels of scrub and alkali resistance. Additionally, the drying time for paint samples incorporating clam shell powder was shorter than that of the control sample.