Custom Building Products PG64317T 17 lb Prism® Grout #643 Warm Gray sets a new standard in cementbased grout technology. Prism's calcium Aluminate cement based formula offers consistent color with no shading regardless of tile type, temperature or humidity. The rapid setting formula results in high early strength and dense joints for the highest stain resistance in grout joints up to 1/2". A unique blend of lightweight recycled glass and fine aggregate sand allows for a smooth consistency that is easy to spread and clean.