The new ASTM C 1142, Standard Specification for Ready-Mixed Mortar for Unit Masonry, finally gives architects and contractors the assurance that this space-age masonry material meets minimum requirements. Among its many benefits, ready mixed mortar provides uniform quality. Each tub is batched and mixed the same way at a plant or in a batcher-mixer truck on the jobsite. Ready mixed mortar also eliminates the cost of mixers, backup mixers, and the mixer operator. FOUR MORTAR TYPES The new standard sets minimum property requirements for four types of ready mixed mortar: RM, RS, RN, and RO. Four cement combinations can be used: portland cement only; portland cement and lime; masonry cement only; or masonry cement and portland cement. FIELD MORTAR MUST MEET SPECS TOO Unlike C 270, C 1142 is a property specification only. C 1142 differs from C 270 in another important way. In C 270, only the mortar made in the lab must meet those specifications. In C 1142, both the laboratory and the field mortar must be tested and conform to the specifications. TESTING THE MORTAR C 1142 details how tests should be performed. Determine the consistency by the cone penetration method. Measure air content by the pressure or volumetric method. Evaluate water retentivity by ASTM C 91. Measure compressive strength following Section A6 of ASTM C 780.