Thixo-Carb® 500 precipitated calcium carbonate (pcc) is a unique surface coated, ultrafine pcc of uniform particle size designed specifically for use in polyurethanes, epoxy and butyl polymeric sealant systems. Controlled particle size and narrow distribution coupled with the unique surface coating, combined to form a rheologically additive providing thixotropy and viscosity control resulting in improved sag and slump characteristics. In addition the semi-reinforcing nature of Thixo-Carb® 500 pcc yields improved physical properties providing the formulator flexibility in designing a cost efficient, high performance sealant system.