While most problems in concrete floors are traceable to poor design practices, it also is also true that the floor can not be better than the concrete that is in it. A poorly designed mix can be difficult to place and finish; it certainly will be costly to repair. An over-designed mix wastes money. The contractor who has an understanding of the ingredients and proportions in a good floor mix will be able to eliminage problems and save money. Workability and good consolidation depend in part on th euse of well-graded aggregates. Coarse aggregate should conform to grading reommended in ASTM C33 "Concrete Aggregates" or ASTM C330 "Lightweigh Aggregates for Sturcural Concrete." Because of the special requirements of concrete floors fine aggregates gradings often differ from these ASTM recommendatins. The preferred gradings for fine aggregates are given in the ACI 302 Standard. Hardness of aggregates is an essential attribute when high wear resistance is desireable. Quartz or traprock are used as hard aggregates for heavy duty floors, usually in a wearing surface of three-fourths of and inch or more thickness. Other special purpose aggregates include quartz, marble, granite and ceramic materials used for decorative purpose. The various kinds of admixtures perform several useful functions in concrete.