Floating

If a smoother surface is required than the one obtained by screeding, work the surface sparingly with a wood or aluminum magnesium float, as shown in Figure 69, or with a finishing machine.

In Figure 70, the aluminum magnesium float is shown in use.

A long handled wood float is used for slab construction, as shown in Figure 71. The aluminum float, which is used in 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.

Begin bull floating immediately after screeding while the concrete is still plastic and workable. 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.