A wellbore cement composition includes substantially unhydrated cement powder and additive powder for cement. The additive powder is formulated from ingredients including a liquid additive for cement and solid carrier particles. The liquid additive is absorbed by the solid carrier particles. A wellbore cementing method includes using a dry cement composition, adding water to the dry cement composition, forming a cement slurry, placing the slurry in a wellbore, and setting the placed slurry. The dry cement composition contains substantially unhydrated cement powder and retarder powder for cement. The retarder powder contains a retarder absorbed by solid carrier particles.