Finishing may be defined as the process of leveling, smoothing, compacting and otherwise treating surface of fresh concrete or recently placed concrete to produce desired appearance.
Steps Involved for Finishing Concrete
There are 3 different steps involved for finishing concrete, which are as given below.
1. Screeding (Step-1)
This is the process of striking off the excess concrete to bring the top surface to proper grade. While depositing concrete its thickness is kept slightly more than final finish. It is then moved by a ‘strike off’ board known as screed. A sawing motion of the screed is used as it moves on the side forms. Handles are attached to each end of the screed. When the distance between the side forms is more than 2 m, the screed is worked by two men.
After screeding, voids left on the surface are filled with concrete and the process is repeated till uniform surface results. When the mix is dry, screed is also used as a tamper to bring mortar to the top for later finishing. Excessive tamping should be avoided. If the mix is dry, adjustments in its proportions should be made. For large jobs screeds can be fixed with rollers which move on side forms. Vibrators can also be fixed on screeds. Concrete should not be overworked. This brings an excessive amount of mortar and water on the surface. This results in low strength.
2. Floating (Step-2)
Floating consists in removing the irregularities on the surface of concrete which are left after screeding. This is done with a wooden float. It is about 1.5 m long and 20 cm wide, attached with a handle. Low spots are filled with concrete and worked with float. Filling low spots with mortar should be avoided as it results in soft non-uniform surface. Finishing is done with the forward and backward motion of the float. In places where it is difficult to operate a long handle float, a wooden float 60 cm long and 10 to 12 cm wide with a handle can be used.
If the area of slab is large and there are no walls and posts, bull float is used. It serves the same purpose as a float. It consists of a wooden or aluminium blade 2 cm wide and 1.0 to 1.5 m long. It is attached to a handle 5 m long. It permits floating without the operators getting on the concrete.
3. Trowelling (Step-3)
It is the final operation of finishing. It provides a smoother finish which is hard and abrasion resistant. Trowelling may be necessary to finish points not finished in a satisfactory manner by floating. It should be done after all excess water has evaporated. Trowelling with a steel float when the concrete is almost dry gives a very smooth finish. The trowel is 25 to 50 cm long and 8 to 12 cm wide. The blades give better service after they have been used enough. Power trowels can also be used for very large works.