SURFACE FINISHING OF CONCRETE

In some situations, where a non-slip surface is required, the finish provided by the tamping process is left as it is and no more surface finishing is carried out. Where a smooth surface is required, finishing of concrete should take place straight away after placing and compaction. The surface should first be lightly trowelled over with a steel floating trowel. If this is done excessively a layer of laitance (very watery cement slurry) will be brought to the surface. This laitance makes subsequent floating of the surface difficult and leaves patches on the surface of the finished concrete that are porous and less durable.

Depending on the setting rate, the surface should be floated after 2-3 hours, using a wooden or polyurethane float in a circular motion. This will flatten any lumps or high spots and fill any dips or hollows in the surface whilst at the same time bringing some moisture to the surface.

At this point, a stainless-steel floating trowel can be run over the surface to provide a final smooth finish. Care should be taken not to over-trowel the finished concrete as this can bring more water to the surface, which will bring with it very fine particles of aggregate. When the concrete hardens, the fine, unbound particles are left behind on the surface, forming a dust when dislodged by any surface friction.

SURFACE FINISHING OF CONCRETE

Fig. 16 Polyurethane float.

SURFACE FINISHING OF CONCRETE

Fig. 17 Stainless steel floating trowel.