HAND TAMPING

Hand tamping, or jitterbugging (figure 7-46), is done after the concrete has been screeded. Hand tamping is used to compact the concrete into a dense mass and to force the larger particles of coarse aggregate slightly below the surface. This enables you to put the desired finish on the surface. The tamping tool should be used only with a low-slump concrete, and bring only just enough mortar to the surface for proper finish. After using the jitterbug, you can go directly to using the bull float.

FLOATING

If a smoother surface is required than the one obtained by screeding, the surface should be worked sparingly with a wood or aluminum magnesium float (figure 7-47, view A) or with a finishing machine. In view B, the wood float is shown in use. A long-handled wood float is used for slab construction (view C). The aluminum float, which is used the same way as the wood float, gives the finished concrete a much smoother surface. To avoid cracking and dusting of the finished concrete, begin aluminum floating when the water sheen disappears from the freshly placed concrete surface. Do not use cement or water as an aid in finishing the surface.

Floating has three purposes: (1) to embed aggregate particles just beneath the surface; (2) to remove slight imperfections (high and low spots); and, (3) to compact the concrete at the surface in preparation for other finishing operations.

Figure 7-47.-Wood floats and floating operations.

Begin floating immediately after screeding while the concrete is still plastic and workable. However, do not overwork the concrete while it is still plastic because you may bring an excess of water and paste to the surface. This fine material forms a thin, weak layer that will scale or quickly wear off under use. To remove a coarse texture as the final finish, you usually have to float the surface a second time after it partially hardens.

EDGING

As the sheen of water begins to leave the surface, edging should begin. All edges of a slab that do not abut another structure should be finished with an edger (figure 7-48). An edger dresses corners and rounds or bevels the concrete edges. Edging the slab helps prevent chipping at the corners and helps give the slab a finished appearance.

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