A slaked lime-based coating material composition which gives a consideration to sick house syndrome is a powdery composition obtained by mixing either calcium hydroxide or a calcium hydroxide/magnesium hydroxide mixture with one or more carrageenans comprising a six-membered-ring galactose skeleton and bonded thereto in equatorial conformation a sulfate group(--OSO.sub.3.sup.-) and a hydroxyl group(--OH) and which is kneaded together with water at time of use, or a slaked lime-based plastering material composition which gives a consideration to sick house syndrome is a pasty slaked lime-based coating material composition obtained by mixing either calcium hydroxide or a calcium hydroxide/magnesium hydroxide mixture with one or more carrageenans comprising a six-membered-ring galactose skeleton and bonded thereto in equatorial conformation a sulfate group(--OSO.sub.3.sup.-) and a hydroxyl group(--OH), and which is kneaded together with water in advance. The carrageenan has long been utilized in food additves so that the carrageenan is highly safe. Since the carrageenan is a water-soluble natural polysaccharide, it rapidly dissolves on mixing with slaked lime and kneading with water. The carrageenan further has excellent water holding, viscosity control and, hence, excess water absorption into bases, e.g., walls, is prevented. The compositions are improved in adhesive properties to bases, workability, and water resistive properties.