All masonry grout contains cementitious materials, aggregates, and water mixed to a highly fluid consistency. The exact proportions of these ingredients depend on the compressive strength requirements of the design, the type and properties of the masonry units, and the sizes of cavities to be filled. Adding other common and proprietary chemicals can increase or reduce the rate at which the grout sets, improve its pumpability, and compensate for shrinkage. However, ASTM C 476 requires that any admixtures used be specified by the architect or engineer or approved by the contractor.