Coming on fast in the last few years is the high-pressure water-jet method of preparing horizontal construction joints for the next placement of concrete. For many years, the Bureau of Reclamation specification for massive hydraulic structures have required that sandblasting be used to remove laitance and provide a roughened surface on concrete before making the next placement. Lifts are usually 7 and one-half feet high and, to maintain shear strength and avoid seepage between bond and continuity of the concrete be obtained at horizontal construction joints. Wet sandblasting does indeed create an excellent surface for this purpose. However, some tests and observations of concrete construction employing high-pressure water-jet blasting indicated that equally good results could probably be obtained by this process, and possibly with some economic advantage. Hence the Bureau decided to include water-jet cleanup in its specifications as an alternative to wet sandblasting, provided that this process would produce equivalent results. The contracting firm for the Pueblo dam elected to use the water-jet alternative. The following is a description of the procedure when waterblast cleanup was in progress on a horizontal construction joint surface having an area of about 4,000 square feet. Two guns were in use, both operating from a single high pressure piston pump unit. Using a sweeping motion, with the gun tip about four or five inches from the surface, a width of about three inches was being covered in a span of three to four feet. Laitance was quickly removed, roughening the concrete surface and exposing the aggregate. There was no indication of undercutting the larger particles of aggregate, which appeared to remain firmly embedded in the matrix. Reportedly, it takes two men six hours to prepare the 4,000 square foot surface. Water is used at a rate of about 10 to 20 gallons per minute.