Concrete slabs with exposed aggregate finishs are becoming increasingly popular for swimming pool decks, patio floors, driveways and sidewalks. The following discussion is a description of a good method that does not require retardants or any special admixtures. The labor involved is little more than what is required for a steel trowel finish.
Slabs should be cast monolithically with a mix as follows: portland cement, 1 part by weight, three-eighths inch and smaller pea gravel, 3.2 parts by weight, and concrete sand, 2.3 parts by weight. Water should be carefully controlled to hold the slump as low as practicable for workability.
In placing the concrete, usual procedures should be followed with respect to spreading and screed leveling. Following the straightedge, the slab should be wood floated with darbles or bull floats until the surface is level and properly sloped to drains. The slab is ready for washing when the initial chemical set has occurred from bottom to top, the water sheen has completely disappeared, and the concrete will support the weight of a man without deflection. The type of brush used is also important. The bristle must be nylon because nylon bristles retain the same degree of stiffness after becoming wet. The washing operation should begin at a corner of the slab on the high side. Only one pass is allowed, therefore, the paste that is washed away must be carried forward continuously to the edge of the slab. After washing, normal curing practices should be employed.