The use of the standard slump cone for the design and quality control of slurry-wall backfill construction is widely employed. This technique, directly from concrete specifications, is suited to a rapid field test during construction, but not so rapid in the lab during design. Laboratory samples of backfill are typically of less volume than one slump cone. A smaller version of the standard, concrete slump cone test is shown to correlate favorably with actual standard slump cone data, and a correlation curve is derived empirically over a range of slump from four to nine inches. The standard slump (in inches) has been found to be two times the lab slump, plus two inches.