Introduced about 12 years ago, integral water repellents are designed to decrease the water permeance of concrete masonry, making unnecessary the application of a water-repellent surface coating. Types of integral water repellents include polymeric admixtures, calcium stearates, and tall oils. All are mixed throughout the concrete during block production. Concerned about masonry's perceived propensity to leak, more and more architects today are specifying integral-water-repellent concrete masonry, especially for use in single-wythe construction. By inhibiting the passage of water through block, the admix also can help reduce efflorescence. Manufacturers of integral water repellents for block make compatible mortar additives that must be added on-site. The water-repellent block and mortar additive function as a system and must be used together. If the mortar admixture is left out, the mortar will not be water-repellent and will allow water to enter the wall.