The C.L. Industries TSSWO is a 50 lb White Thin Set Sanded Bag. Sanded Thin Set is a factory blend of portland cement, sand and special additives. It’s an excellent dry set mortar for floor tile installations. CLI Sanded Thin Set is preferred for backing on plumb and true masonry concrete, gypsum board (dry areas only), WonderBoard® Backerboard, cured Portland cement mortar beds, brick, ceramic tile and marble. It requires no soaking of tiles and is not affected by prolonged contact with water, so it works beautifully with both interior and exterior projects.